pubs.acs.org/Organometallics Published on Web 02/10/2011 r 2011 American Chemical Society
1182 Organometallics 2011, 30, 1182–1201
DOI: 10.1021/om101167p
Reactions of Cyclopentadienyl-Amidinate Titanium Hydrazides
with CO2, CS2, and Isocyanates: TidNr Cycloaddition,
Cycloaddition-Insertion, and Cycloaddition-NNR2 Group
Transfer Reactions
Pei JenTiong,†AinaraNova,‡ LauraR.Groom,†AndrewD. Schwarz,† JonathanD. Selby,†
A. Daniel Schofield,† Eric Clot,*,‡ and Philip Mountford*,†
†Chemistry Research Laboratory, Department of Chemistry, University of Oxford,Mansfield Road, Oxford
OX1 3TA, U.K., and ‡Institut Charles Gerhardt, Universit
e Montpellier 2, CNRS 5253, cc 1501, Place
Eugene Bataillon, 34095 Montpellier Cedex 5, France
Received December 10, 2010
We report a comprehensive combined experimental and DFT investigation of the synthesis,
molecular and electronic structures, and reactivity of terminal hydrazido complexes with CO2, CS2,
isocyanates, and isothiocyanates. Reaction of Cp*Ti{MeC(NiPr)2}(N
tBu) with hydrazines
R1R2NNH2 gave the structurally characterized series of hydrazides Cp*Ti{MeC(N
iPr)2}(NNR
1R2)
(R1=Ph,R2=Ph (13),Me (14); R1=R2=Me (15)). The energetics of this imide/hydrazine excha-
nge reaction, aswell as the electronic andmolecular structures of 13-15, have been evaluated byDFT
and compared with those of their methyl and phenyl imido counterparts. Reaction of 13-15 with
CO2orCS2 gaveTidNR cycloadditionproducts of the typeCp*Ti{MeC(N
iPr)2}{N(NR2)C(E)E} (R=
Ph, Me; E = O, S) and, in the case of CO2, cycloaddition-insertion products Cp*Ti{MeC-
(NiPr)2}{OC(O)N(NR2)C(O)O}, in which 2 equivs of CO2 had effectively inserted into TidNR.
Reaction of 13 with isocyanates and isothiocyanates also gave stable cycloaddition products.
Cp*Ti{MeC(NiPr)2}{N(NPh2)C(NTol)O} reacted further with CO2 to give a mixed cycloaddi-
tion-insertion product. The tBuNCOmoiety in Cp*Ti{MeC(NiPr)2}{N(NPh2)C(N
tBu)O} could be
displaced by CO2 or TolNCO. In contrast, the reactions of 15 are dominated by cycloaddi-
tion-elimination reactions. Reaction with tBuNCO or Ar0NCO (2 equivs) gave tBuNCNNMe2
or the heterocycle 1,2,4-N(Me)2NC(NAr0)N(Ar0)C(O), respectively, along with [Cp*Ti{MeC-
(NiPr)2}(μ-O)]2. With TolNCO (2 equivs), Cp*Ti{MeC(N
iPr)2}{OC(NNMe2)N(Tol)C(NTol)O}
was formed via a series of cycloaddition-elimination and cycloaddition-insertion steps. The
energetics andmechanisms of the cycloaddition, cycloaddition-insertion, and cycloaddition-extru-
sion processes of various model imido and hydrazido complexes have been investigated using DFT.
In the latter (metathesis) reactions, the reaction outcomes depend on a delicate balance of the relative
affinities of NR or NNR2 for the metal center or the organic fragment (CO, CS, or RNC).
Introduction
Since being established 20 years ago,1-4 the chemistry of
terminal titanium imido compounds (L)TidNR (R= alkyl,
aryl) has advanced enormously. Much of this progress has
been charted in a series of reviews,5-11 and most of the
interest in this chemistry concerns reactions of the polar and
unsaturated TidNR multiple bond itself (formally a σ2π4
triple bond in most instances12-14), which can undergo
coupling or exchange with a range of unsaturated substrates.
As a development of our work in titanium imido chemistry
we have become interested in exploring the apparently
related hydrazido complexes (L)TidNNR2. The chemistry
*To whom correspondence should be addressed. Email: clot@
univ-montp2.fr (E.C.); philip.mountford@chem.ox.ac.uk (P.M.).
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Article Organometallics, Vol. 30, No. 5, 2011 1183
of well-defined examples of these species was hardly developed
at all until relatively recently, although they had been postu-
lated as intermediates in hydrohydrazination catalysis.15-21
While the first report of a terminal titanium hydrazide was in
1978,22 the first structurally characterized examples only ap-
peared in 2004 and 2005.17,23 Similarly, the first fully authenti-
cated [2 þ 2] cycloaddition product of any group 4 hydrazide
was reported only in 2008.24
One very distinctive feature of titanium hydrazides and
their zirconium congeners is their tendency to undergo facile
N
R
-N
β
bond insertion or cleavage with substrates such as
alkynes, isonitriles, CO, and heavier chalcogen sources,
processes that are unavailable to their imido coun-
terparts.24,30-35 For example, Ti(N2N
py)(NtBu) reacts with
XylNC and PhCCMe to form 1 and 2 (Figure 1), involving
coupling or addition reactions across the TidN multiple
bond.25,26 In contrast, Ti(N2N
py)(NNPh2)(py) forms 3 and 4
with the same substrates. Mechanistically,31,32 these reac-
tions also proceed via addition to TidN
R
but then lead on to
N
R
-N
β
bond scission. The latter steps formally involve
reduction of the nitrogen atoms of the original TidN-NPh2
linkage from 2- in Ti(N2N
py)(NNPh2)(py) to 3- in the
products and a corresponding net two-electron oxidation
of the substrates. Accordingly, reactions of group 4 hydra-
zides with nonoxidizable substrates such as CO2, isocya-
nates, and organic nitriles do not give N
R
-N
β
bond
reduction and stop at TidN
R
cycloaddition or inser-
tion.24,32,36-39
We have been trying to gain a better knowledge and
understanding of the reactions of the hydrazideMdN
R
bond
both in general terms and in comparison with relevant imido
counterparts and also as a function of different β-nitrogen
groups which are known to have significant effects on
molecular and electronic structure. This aspect of hydrazido
chemistry is totally underdeveloped for the following rea-
sons. First, it is only for the recently developed group 4
systems that any significantMdN
R
bond reactivity is seen at
all, despite studies of group 6 hydrazido complexes for many
Figure 1. Influence of N
R
substituents on reaction outcomes in imido and hydrazido chemistry (top) for reactions of Ti(N2N
py)-
(NR)(py) (R = tBu, NPh2) with XylNC or PhCCMe;
25,26 (bottom) for reactions of Cp*Ti{MeC(NiPr)2}(NR) (R =
tBu, Ar) with
CO2.
27-29 Atoms derived from the original TidNR group are shown in red, while those originating from the organic substrate are
shown in blue.
(15) Cao, C.; Shi, Y.; Odom, A. L. Org. Lett. 2002, 4, 2853.
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Jones, C.; Mountford, P. Chem. Commun. 2008, 5101.
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1184 Organometallics, Vol. 30, No. 5, 2011 Tiong et al.
years.40,41 The more dative (donor/acceptor) nature of the
group 6Mr:N
R
bond and reduced multiple-bond character
reduces its reactivity. Second, with formally oxidizable sub-
strates, N
R
-N
β
bond scission readily occurs, effectively
masking the initial MdN
R
bond reaction. Finally, with
regard to comparing different N
β
R2 groups, there are rela-
tively few homologous pairs or series of complexes of this
type.42-44 A significant cause of this problem is the well-
established tendency of group 4 N
β
-dialkyl-substituted hy-
drazides to dimerize, forming unreactive M2(μ2-NNR2)2
moieties.17,23,44
Although we had previously reported the series of well-
defined terminal hydrazides Ti(Me2Calix)(NNR
1R2) (5; R1 =
R2 = Ph, Me; R1 = Ph, R2 = Me) with the aim of making
a comparative study of the various TidNNR1R2 groups,
their negligible intrinsic reactivity caused this approach to
fail.43 To date, only one report has appeared describing
comparative reactions of differently N
β
-substituted MdN-
NR2 functional groups.
37 Here Gade et al. found rather
similar [2 þ 2] cycloaddition reaction chemistry between
Cp*Ti(NXylN)(NNR1R2)(L) (6; R1 = R2 = Ph, L= tBuN-
H2; R
1 = Ph, R2 = Me, L = py; Xyl =3,5-C6H3Me2) and
phenylallene, PhNCO, and PhNCS. Reactions of the di-
methylhydrazido homologue Cp*Ti(NXylN)(NNMe2)(L)
(which has a tendency to lose L and dimerize) with these
substrates was not reported.
In a renewed attempt to develop the chemistry of the
hydrazide TidN
R
bond, we decided to target hydrazido
analogues of the tert-butyl and aryl imido complexes Cp*Ti-
{MeC(NiPr)2}(NR). These undergo a number of different
transformations of the TidNR bond with a wide range of
nonoxidizable substrates, namely CO2, CS2, COS, RNCO,
RNCS, PhNO, RCONH2, and RCOR0.
27-29,45,46 These
systems, which have been studied in detail both by experi-
ment and by DFT, are also rather sensitive to the identity of
the imido N substituent, making them good candidates for
developing hydrazido chemistry. For example, reaction of
both Cp*Ti{MeC(NiPr)2}(N
tBu) (7) and Cp*Ti{MeC-
(NiPr)2}(NAr) (8, Ar = Tol, 4-C6H4CF3, 4-C6H4NMe2,
2,6-C6H3Me2) with CO2 forms the [2 þ 2] cycloaddition
products 9 and 10 (Figure 1). However, while 8 reacts with
further CO2 to form the “double insertion” product 11, the
tert-butyl homologue does not, giving instead tBuNCO
extrusion and the μ-oxo dimer [Cp*Ti{MeC(NiPr)2}(μ-O)]2
(12).
In this contribution we report a comprehensive combined
experimental and DFT investigation of the synthesis, struc-
tures, and reactivity of cyclopentadienyl-amidinate hydra-
zido complexes. A part of this work has been communic-
ated.39
Results and Discussion
Synthesis and Molecular Structures of New Titanium Hy-
drazido Complexes. The new hydrazido compounds Cp*Ti-
{MeC(NiPr)2}(NNR
1R2) (R1 = Ph, R2 = Ph (13), Me (14);
R1 = R2 = Me (15)) were prepared from Cp*Ti{MeC-
(NiPr)2}(N
tBu) (7) and the corresponding hydrazines at
room temperature according to eq 1 using the tert-butyl
imide-hydrazide exchange strategy introduced by us
previously.36 An analogous approach had also proved suc-
cessful for preparing the aryl imido complexes Cp*Ti{MeC-
(NiPr)2}(NAr) (8).
29,46 Compounds 13 and 15 were isolated
as yellow or dark green solids in 83 and 67% optimized
yields, respectively, while 14 (34% yield) was a very soluble
green-brown, waxy material that was hard to crystallize and
purify. Attempts to vary the cyclopentadienyl-amidinate
supporting ligand set in a way that was successful for the
analogous aryl imido systems46 were unrewarding. Treat-
ment of Cp*Ti{PhC(NSiMe3)2}(N
tBu)47 with Ph2NNH2 in
toluene-d8 at room temperature or 100
C for 3 days gave no
reaction. With Me2NNH2, no reaction occurred at room
temperature, while at higher temperatures an unknown
mixture of products was formed. Reactions of Cp0Ti{PhC-
(NSiMe3)2}(N
tBu)46 (Cp0 = C5H4Me) with Ph2NNH2 and
PhMeNH2 were more promising, but the products were oils
and again were difficult to manipulate and purify.
The 1H and 13C NMR data for 13-15 are consistent with
the Cs-symmetric half-sandwich structures depicted in eq 1.
Diffraction-quality crystals of all three were grown from
pentane. The molecular structures are shown in Figures 2
and 3, and selected distances and angles are given in Table 1.
The compounds possess a three-legged piano-stool geometry
around titanium with η5-C5Me5 and κ
2N,N0 acetamidinate
ligands. The metric parameters associated with the Cp*Ti-
{MeC(NiPr)2} fragments are similar in all three and are
comparable to those reported previously for imido com-
pounds of the type CpRTi{R1C(NR2)2}(NR
3).29,46 Themain
point of interest is the variation in the TidNNR1R2 linkages
as a function of the β-N substituents. One such homologous
series has been structurally characterized previously, namely
Ti(Me2Calix)(NNR
1R2) (5;R1=Ph,R2=Ph,Me;R1=R2=
Me). Gade et al. have also structurally characterized the
series Cp*Ti(NXylN)(NNR1R2)(L) (6) with the same hydra-
zide ligands as in 13-15 and 5, but here the donor ligand L
(42) Patel, S.; Li, Y.; Odom, A. L. Inorg. Chem. 2007, 46, 6373.
(43) Clulow, A. J.; Selby, J. D.; Cushion, M. G.; Schwarz, A. D.;
Mountford, P. Inorg. Chem. 2008, 47, 12049.
(44) Weitershaus, K.; Wadepohl, H.; Gade, L. H. Organometallics
2009, 28, 3381.
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Mountford, P. Dalton Trans. 2002, 4175.
(46) Guiducci, A. E.; Boyd, C. L.; Mountford, P. Organometallics
2006, 25, 1167.
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17, 3271.

Article Organometallics, Vol. 30, No. 5, 2011 1185
(py, DMAP, or none) varies in each case, making precise
comparisons difficult.
In general terms, the TidN
R
and N
R
-N
β
distances and
angles subtended at N
R
and N
β
are comparable to those of
(L)TidNNR1R2 complexes reported previously (R1, R2 =
alkyl, aryl, H).48,49 The short average TidN
R
bond distance
of 1.730 A˚ and approximately linear TidN
R
-N
β
angle
(average 163
) are consistent with a σ2π4 triple bond and
formally dianionic [NNR1R2]2- ligands (see below for a
DFT analysis).23,42,50 The N
β
atoms for the phenyl-substi-
tuted compounds 13 and 14 are planar within error (due to
conjugation of the lone pair with the phenyl ring(s)),42,50
whereas that of 15 is pyramidal. The sum of the angles
subtended at N(2) in this case is 334.3(2)
, close to that
expected for formal sp3 hybridization (328.4
). The TidN
R
and N
R
-N
β
distances for 13 and 14 are identical within
error, whereas those for 15 are shorter and longer, respec-
tively. A similar trend in N
R
-N
β
distance was found for the
calixarene-supported compounds 5, and group 4N
β
-dialkyl-
substituted hydrazides generally have longer N
R
-N
β
dis-
tances and pyramidal N
β
atoms.48,49 The N
R
-N
β
single
bond in free Me2NNH2 (1.436(2) A˚, pyramidal NMe2) is
likewise longer than that in Ph2NNH2 (1.418(2) A˚, planar
NPh2), apparently due to Nβ hybridization effects.
50,51
The TidN
R
distances for 13 and 14 are equivalent within
error to the value of 1.738(2) A˚ found for TidN in the aryl
imide Cp*Ti{MeC(NiPr)2}(N-2,6-C6H3Me2), while that of
15 is significantly shorter.46 Within the series 13-15 the
TidN
R
bond distances vary in the order TidNNPh2 ≈
TidNNMePh > TidNNMe2, with Δ(TidNR) = 0.011(3)
A˚ between 15 and 13 or 14. In contrast, the corresponding
distances for Ti(Me2Calix)(NNR
1R2) (5) vary in the oppo-
site way with TidNNPh2 < TidNNMePh ≈ TidNNMe2
(1.717(2), 1.727(3), and 1.729(4) A˚, respectively),43 although
all were longer than TidN in Ti(Me2calix)(N
tBu) (1.705(3)
A˚).52 To explore this further, we used DFT to calculate the
geometries of the simplified model imido and hydrazido
compounds CpTi{MeC(NMe)2}(NR) (R = Me (1Me), Ph
Figure 2. Displacement ellipsoid plots (25% probability) of (a) Cp*Ti{MeC(NiPr)2}(NNPh2) (13) and (b) Cp*Ti{MeC(N
iPr)2}-
(NNMePh) (14). H atoms are omitted for clarity.
Figure 3. Displacement ellipsoid plot (20% probability) of
Cp*Ti{MeC(NiPr)2}(NNMe2) (15). H atoms are omitted for
clarity. Atoms carrying the suffix “A” are related to their
counterparts by the symmetry operator x, y, -z þ 3/2).
Table 1. Selected Bond Lengths (A˚) and Angles (deg) for Cp*Ti-
{MeC(NiPr)2}(NNPh2) (13), Cp*Ti{MeC(N
iPr)2}(NNMePh)
(14), and Cp*Ti{MeC(NiPr)2}(NNMe2) (15)
a
param 13 14 15
Ti(1)-Cpcent 2.097 2.067 2.063
Ti(1)-N(1) 1.734(2) 1.734(2) 1.723(2)
Ti(1)-N(3) 2.115(2) 2.110(2) 2.101(1)
Ti(1)-N(4) 2.099(2) 2.090(2)
N(1)-N(2) 1.369(2) 1.371(3) 1.386(2)
N(2)-C(1) 1.409(3) 1.396(4) 1.461(2)
N(2)-C(7) 1.425(3) 1.460(4)
Cpcent-Ti(1)-N(1) 121.4 121.1 119.5
Cpcent-Ti(1)-N(3) 120.8 121.8 120.8
Cpcent-Ti(1)-N(4) 119.6 119.7
N(3)-Ti(1)-N(4)/N(3A) 64.23(7) 64.44(9) 64.45(7)
Ti(1)-N(1)-N(2) 163.9(1) 166.3(2) 159.5(1)
N(1)-N(2)-C(1) 118.9(2) 118.2(2) 110.7(1)
N(1)-N(2)-C(7)/C(1A) 116.7(2) 115.3(2) 110.7(1)
C(1)-N(2)-C(7)/C(1A) 121.5(2) 120.8(2) 112.9(2)
aCpcent is the computed Cp* ring carbon centroid. Atoms carrying
the suffix “A”are related to their counterparts by the symmetry operator
x, y, -z þ 3/2.
(48) Allen, F. H.; Kennard, O.Chem. Des. Automation News 1993, 8,
1&31.
(49) Fletcher, D. A.; McMeeking, R. F.; Parkin, D. J. Chem. Inf.
Comput. Sci. 1996, 36, 746(the UK Chemical Database Service, CSD
version 5.31 updated Aug 2010).
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P. Organometallics 2008, 27, 6479.
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1186 Organometallics, Vol. 30, No. 5, 2011 Tiong et al.
(1Ph)) and CpTi{MeC(NMe)2}(NNR
1R2) (R1 = Ph, R2 =
Ph (1NPh2), Me (1NMePh); R
1 = R2 = Me (1NMe2)), as
illustrated in Figure 4. A furthermodel was calculated on the
basis of CpTi{MeC(NMe)2}(NNMe2), but this time with a
constrained NNMe2 group in which the geometry at Nβ was
forced to be planar (1NMe2_planar). Model 1NMe2_planar
was 4.6 kcal mol-1 less stable than the fully relaxed 1NMe2.
Full details of the structures are provided in the Supporting
Information.
DFT Analysis of Molecular and Electronic Structures and
Imide-Hydrazine Exchange Energies. The DFT trend in
TidN
R
distances (TidNNPh2≈TidNNMePh>TidNNMe2
(1)) for the model hydrazides 1NPh2, 1NMePh, and 1NMe2 is
consistent with that observed experimentally, although the
computeddistances are systematically shorter due to the reduced
bulkof themodels. The trends inN
R
-N
β
distances andangles at
N
R
and N
β
are likewise consistent. In particular, the longest
N
R
-N
β
distance is associated with the shortest TidN
R
(i.e., 1NMe2) and vice versa. The reason for the longer TidNR
distance in 1NPh2 and 1NMePh is better conjugation of the Nβ
lone pair (N
β
-LP) with TidN
R
as a result of the planarity at N
β
.
Consistent with this, on forcing the N
β
atom of 1NMe2 to be
planar (giving 1NMe2_planar), there was a 0.011 A˚ lengthening
of TidN
R
and a 0.031 A˚ shortening of N
R
-N
β
compared to
1NMe2. The better conjugation of Nβ-LP in 1NMe2_planar is
illustrated by a 24 kcal mol-1 increase in the donation of N
β
-LP
into the TidN
R
π* bond, as obtained in the NBO second-order
perturbation analysis of donor-acceptor interactions.A smaller
shortening of the N-Me distances (0.018 A˚) was also seen,
attributed to the reduction in covalent radius on going from an
sp3 to an sp2 N
β
.
The TidNPh distance in 1Ph lies between those of 1NPh2
and 1NMe2, which is slightly different from the experimental
situation for Cp*Ti{MeC(NiPr)2}(N-2,6-C6H3Me2), but
steric effects associated with 2,6-C6H3Me2 could lengthen
the TidNAr bond. The TidNMe distance in 1Me was the
shortest of all, consistent with previous structural compar-
isons of homologous pairs of titanium alkyl and aryl imido
complexes.53-56 The longer TidN bond distance in 1Ph
compared to that in 1Me is due to a π-accepting character
of the Ph group, as illustrated by the larger donation (by 14
kcal mol-1) from TidN π to π* on Ph compared to the
reverse donation from π on Ph toward TidN π*. Such
electron transfer interactions are absent in 1Me.
Overall, the experimental andDFT results show that while
alkyl imides should have the shortest TidN
R
bonds, those for
aryl imide and alkyl or aryl hydrazide ligands are more
similar to each other.With respect to the TidNNR2 systems,
the geometry at N
β
has the greatest influence on the TidN
R
and N
R
-N
β
bond lengths. For a planar N
β
the different
substituents have a smaller but noticeable (for the DFT
models) effect on the TidN
R
and N
R
-N
β
distances.
As mentioned, compounds 13-15 were prepared from 7
and the appropriate hydrazine using an exchange strategy
well established previously for aryl imido complexes. To gain
additional insights into the underlying energetics of these
reactions (which experimentally all proceed to completion),
we computed the energies of the isodesmic processes in
Figure 5 using the model systems in Figure 4. The tert butyl
imide-hydrazine exchange reactions are all somewhat more
favorable than those with PhNH2. Ph2NNH2 provides the
most energetically favorable exchange reaction, but there is
little difference between the three hydrazines studied.
We have also compared the computed electronic structures
of the TidNR and TidNNR2 linkages for the model systems
1Me through 1NMe2. The electronic structures of titanium
imido compounds have been studied in detail,9,12-14,57-60
and a number of DFT investigations of the bonding in
hydrazides have also been reported.23,42,50,61-63 There has been
one DFT report comparing the electronic structure of
Figure 5. DFT computed electronic energies (kcal mol-1) for
the isodesmic reactions illustrated. [Ti] represents CpTi{MeC-
(NMe)2}.
Figure 4. Model complexes used in the DFT calculations. Selected distances (A˚): TidN = 1.688 (1Me), 1.709 (1Ph), 1.713 (1NPh2),
1.714 (1NMePh), 1.716 (1NMe2_planar), 1.705 (1NMe2); NR-Nβ = 1.345 (1NPh2), 1.339 (1NMePh), 1.329 (1NMe2_planar), 1.360
(1NMe2).
(53) Blake,A. J.; Collier, P. E.;Dunn, S. C.; Li,W.-S.;Mountford, P.;
Shishkin., O. V. J. Chem. Soc., Dalton Trans. 1997, 1549.
(54) Collier, P. E.; Dunn, S. C.; Mountford, P.; Shishkin, O. V.;
Swallow, D. J. Chem. Soc., Dalton Trans. 1995, 3743.
(55) Adams, N.; Arts, H. J.; Bolton, P. D.; Cowell, D.; Dubberley,
S. R.; Friederichs, N.; Grant, C. M.; Kranenburg, M.; Sealey, A. J.;
Wang, B.; Wilson, P. J.; Zuideveld, M. A.; Blake, A. J.; Schr€oder, M.;
Mountford, P. Organometallics 2006, 25, 3888.
(56) Adams, N.; Bigmore, H. R.; Blundell, T. L.; Boyd, C. L.;
Dubberley, S. R.; Sealey, A. J.; Cowley, A. R.; Skinner, M. E. G.;
Mountford, P. Inorg. Chem. 2005, 44, 2882.
(57) Cundari, T. R. J. Am. Chem. Soc. 1992, 114, 7879.
(58) Mountford, P.; Swallow, D. J. Chem. Soc., Chem. Commun.
1995, 2357.
(59) Bolton, P. D.; Clot, E.; Adams, N.; Dubberley, S. R.; Cowley,
A. R.; Mountford, P. Organometallics 2006, 25, 2806.
(60) Feliz,M.; Bolton, P.D.;Clot, E.;Mountford, P.Organometallics
2008, 27, 6111.
(61) Herrmann, H.; Fillol, J. L.; Gehrmann, T.; Enders, M.;
Wadepohl, H.; Gade, L. H. Chem. Eur. J. 2008, 14, 8131.
(62) Kahlal, S.; Saillard, J.-Y.; Hamon, J.-R.; Manzur, C.; Carrillo,
D. J. Chem. Soc., Dalton Trans. 1998, 1229.
(63) Lehnert, N.; Tuczek, F. Inorg. Chem. 1999, 38, 1671.

Article Organometallics, Vol. 30, No. 5, 2011 1187
TidNMe, TidNPh, and TidNNPh2 ligands within the same
supporting ligand framework, namely Ti{HC(pz)3}(NR)Cl2 as
models for real systems of the type Ti{HC(Me2pz)3}-
(NR)Cl2.
23,64-67 The effects of varying the N
β
substituents or
geometry were not assessed.
All six model systems, 1Me through 1NMe2 and 1NMe2_-
planar, have a formal TidN
R
triple bond containing two
principal d
π
-p
π
molecular orbitals which form or contribute
to the three highest MOs of the complexes (see the Support-
ing Information for further details). One MO (denoted πv)
lies in the molecular mirror plane, and the other lies perpen-
dicular to it (πh). The πh energies are relatively insensitive to
the N
R
substituents and vary nonsystematically due to
different degrees of mixing with the out-of-phase 2p
π
con-
tribution of amidinate N atoms. The πv MOs do not mix
significantly with the supporting ligand orbitals and also
interact with the N
R
substituent (Ph, NR2) orbitals. The πv
MOs for the six models are depicted in Figure 6 along with
their energies.
In comparison to CpTi{MeC(NMe)2}(NMe) (1Me), the
phenyl substituent in 1Ph leads to a destabilization of πv by
þ0.49 eV due to a π* antibonding interaction with one of the
occupied ring MOs. This value is within the ranges deter-
mined previously by DFT and/or photoelectron
spectroscopy.14,23 As expected,23,42,50,62,63 introduction of
NNPh2 in 1NPh2 gives a larger destabilization (þ1.23 eV)
due to the N
β
atom lone pair. The πv MO in 1NMePh is
slightlymore destabilized compared to 1NPh2 (þ0.1 eV), and
that in 1NMe2_planar is the least stable (þ0.46 eV, cf. 1NPh2;
þ1.69 eV, cf. 1Me). Allowing 1NMe2_planar to relax to
1NMe2 stabilizes πv by 0.52 eV. The destabilization along
the series 1NPh2, 1NMePh, 1NMe2_planar follows the re-
duction in delocalization of the N
β
lone pair by the phenyl
ring(s) and tracks the changes in TidN
R
and N
R
-N
β
noted
above. The eventual similarity in energy of πv (average 4.23,
range 0.16 eV) for 1NPh2, 1NMePh, and 1NMe2 arises from
two different means of stabilization: conjugation with the
N
β
-phenyl group(s) or N
β
pyramidalization.
Reactions of Cp*Ti{MeC(NiPr)2}(NNR2) (R = Ph (13),
Me (15))withCO2 andCS2.We found that the reactions of 13
or 15withCO2 andCS2were rather similar, and sowe discuss
the two systems alongside each other below. In contrast,
their reactions with isocyanates and isothiocyanates differed
significantly, depending upon the β-NR2 group. These are
discussed later on. We also carried out representative pre-
parative and/or NMR tube scale reactions of Cp*Ti{MeC-
(NiPr)2}(NNMePh) (14) with CO2 and CS2, as described in
the Supporting Information. The reaction outcomes were
analogous to those for 13. For this reason, and the difficulties
in obtaining synthetically useful quantities of 14, we focus
hereafter on 13 and 15. The reactions of 13 and 15 with CO2
and CS2 are summarized in Scheme 1. DFT studies of these
reactions, varying both the TidNRgroup (Ph,NPh2,NMe2)
and the substrate (CO2, CS2, MeNCO), are discussed later
on.
When the reactions of 13 and 15with CO2 (excess, 1.1 atm
pressure) were followed by 1H NMR in C6D6, the first-
formed intermediates Cp*Ti{MeC(NiPr)2}{N(NR2)C(O)O}
(R = Ph (16), Me (17)) were immediately observed. These
subsequently converted into the final products Cp*Ti{MeC-
(NiPr)2}{OC(O)N(NR2)C(O)O} (R = Ph (18), Me (19)).
Under identical conditions, the reaction of 16 with CO2 was
noticeably slower than that of 17. Compounds 16 and 17
were prepared on apreparative scale in ca. 60% isolated yield
by reaction of 13 and 15with an excess of CO2 at-78
C for 5
min. Compounds 18 and 19 were obtained in ca. 70% yield
after more extended reaction times at room temperature
(Scheme 1).
The solution 1H and 13C NMR data for 16 and 17 are
consistent with the C1-symmetric N,O-bound carbamate-
type [2 þ 2] cycloaddition products shown in Scheme 1. For
example, the 1H NMR spectrum of 16 shows two apparent
septets for the inequivalent isopropyl methine hydrogens,
and four doublets for the two pairs of diastereotopic methyl
groups of these substituents. The IR spectra showed bands
at 1684 (16) and 1667 cm-1 (17) attributed to ν(CdO) of the
carbamate ligands. The corresponding absorption for Ti-
(Me4taa){N(NPh2)C(O)O} (formed from Ti(Me4taa)(NNPh2)
andCO2;H2Me4taa=tetramethyldibenzotetraaza[14]annulene)
Figure 6. Isosurfaces and energies of the πv MOs of CpTi{MeC(NMe)2}(NR) (R = Me (1Me), Ph (1Ph), NPh2 (1NPh2), NMePh
(1NMePh), NMe2 (1NMe2 (top right) or 1NMe2_planar (bottom right)).
(64) Bigmore, H. R.; Dubberley, S. R.; Kranenburg, M.; Lawrence,
S. C.; Sealey, A. J.; Selby, J. D.; Zuideveld, M.; Cowley, A. R.;
Mountford, P. Chem. Commun. 2006, 436.
(65) Lawrence, S. C.; Skinner, M. E. G.; Green, J. C.; Mountford, P.
Chem. Commun. 2001, 705.
(66) Dunn, S. C.; Mountford, P.; Shishkin, O. V. Inorg. Chem. 1996,
35, 1006.
(67) Male, N. A. H.; Skinner, M. E. G.; Bylikin, S. Y.; Wilson, P. J.;
Mountford, P.; Schr€oder, M. Inorg. Chem. 2000, 39, 5483.

1188 Organometallics, Vol. 30, No. 5, 2011 Tiong et al.
appears at 1685 cm-1;36 those for imide-derived Cp*Ti{MeC
(NiPr)2}{N(R)C(O)O} (R =
tBu, aryl) are observed between
1672 and 1655 cm-1.29 Compounds 16 and 17 are the second
reported [2þ 2] cycloadditionproducts formedbetweenCO2and
a transition-metal hydrazide. Like the aryl imido derived carba-
mate 10 (Figure 1) they are stable in solution for days at room
temperature and do not eliminate the corresponding aminoiso-
cyanates R2NNCO.
The NMR spectra for 18 and 19 indicate Cs-symmetric
products, and their IR spectra show two strong bands at
1715 and 1676 cm-1 and at 1702 and 1655 cm-1, respectively,
consistent with the incorporation of a second CO2 molecule.
Since the 13C spectra showonly oneC=Oresonance (δ 157.2
ppm), these bands are attributed to the symmetric and
antisymmetric ν(CdO) modes of a dicarboxylate OC(O)N-
(NR2)C(O)O ligand. The corresponding absorptions for the
imido-derived compounds 11 (Figure 1) appear between
1704 and 1694 cm-1 and between 1658 and 1651 cm-1.
Diffraction-quality crystals of both 18 and 19 were grown
by slow evaporation of a diethyl ether solution. The molec-
ular structures are shown in Figure 7, and selected distances
and angles are given in Table 2. These confirm that two
molecules of CO2 have been effectively inserted into the
TidN
R
bonds of 13 and 15. The X-ray structure of the
homologous Cp*Ti{MeC(NiPr)2}{OC(O)N(NMePh)C-
(O)O}, derived from 14, is given in the Supporting Informa-
tion. The distances and angles within the new dicarboxylate
ligands are analogous to those reported for 11.29 The atoms
of the {TiOC(O)N(N)C(O)O} moieties are approximately
coplanar. For 18 the maximum displacement from the least-
squares plane is 0.20 A˚, and for 19 it is 0.14 A˚. The N
R
-N
β
distance for 18 is 0.020(4) A˚ shorter than for 19, reflecting the
different N
β
hybridization. The β-NR2 groups are effectively
“locked” between the two adjacent CdO groups, consistent
with the NMR data, which find two chemically inequivalent
N
β
substituents.
The net “double insertion” of two CO2 molecules into
the TidN
R
bonds of 13-15 is a new transformation for a
metal hydrazido compound (mechanistically, a sequential
Figure 7. Displacement ellipsoid plot (20% probability) of (a) Cp*Ti{MeC(NiPr)2}{OC(O)N(NPh2)C(O)O} (18) and (b) Cp*Ti-
{MeC(NiPr)2}{OC(O)N(NMe2)C(O)O} (19). H atoms omitted for clarity.
Scheme 1. Reactions of Cp*Ti{MeC(NiPr)2}(NNR2) (R = Ph (13), Me (15)) with CO2 and CS2
(68) Glueck, D. S.; Wu, J.; Hollander, F. J.; Bergman, R. G. J. Am.
Chem. Soc. 1991, 113, 2041.
(69) Cooley, J.H.; Evain, E. J.;Willett,R.D.; Blanchette, J. T. J.Org.
Chem. 1989, 54, 1048.

Article Organometallics, Vol. 30, No. 5, 2011 1189
cycloaddition-insertion process). This is also a very unu-
sual process in imido chemistry, having been observed for
either two CO2 or two isocyanates “inserting” into the
TidNAr of 8 or two alkynes into the IrdNtBu bond of
Cp*Ir(NtBu).29,46,68 We have previously reported me-
chanistic studies of this process in the case of 11. Very
recently we reported another TidN
R
bond “insertion”:
namely, the reaction of Ti(N2N
Me)(NNPh2)(py) (N2N
Me
= MeN(CH2CH2NSiMe3)2) with fluorinated benzoni-
triles to give the hydrazonamide complexes Ti(N2N
Me)-
{NC(ArF)NNPh2}(py) (Ar
F = 2,6-C6H3F2, C6F5).
32 This
reaction proceeds via a [2 þ 2] cycloaddition followed by
reverse cycloaddition in the opposite sense.
Reaction of 13 or 15with an excess of CS2 for 16 h at room
temperature afforded the dark brown thiocarbamates
Cp*Ti{MeC(NiPr)2}{N(NR2)C(S)S} (R = Ph (20), Me
(21)) in reasonable yields. The 1H and 13C NMR data are
consistent with the C1-symmetric structures illustrated in
Scheme 1.An analogous product was formedwith 14 (see the
Supporting Information). Longer reaction times did not lead
to “double-insertion” analogues of 18 and 19. However,
whereas 20 and 21 are stable in solution for days, the
corresponding cycloaddition products formed from the imi-
do analogues Cp*Ti{MeC(NiPr)2}(NR) (R =
tBu (7), Ar
(8)) all eliminate RNCS, forming [Cp*Ti{MeC(NiPr)2}
(μ-S)]2.
Since CO2 inserts into the Ti-N bond of 16 to form 18,
we attempted the corresponding reaction of CS2 with 16
with the hope of forming a mixed CO2/CS2 “double
insertion” product. Surprisingly, this led to 20 (major
product, ca. 80%) along with 18 after 16 h in C6D6 (eq 2).
Compound 18 is presumably formed by reaction of 16
with displaced CO2. In contrast, exposure of 20 to an
excess of CO2 (1.1 atm) for several days gave no reaction.
Given the established reversibility of heterocumulene
addition to the TidNR bonds of 7 and 8 and other
reactions discussed below, eq 2 probably proceeds via a
dissociative mechanism transiently forming 13. Overall
these results suggest that [2 þ 2] cycloaddition of CS2 to
the TidNNPh2 bond of 13 is thermodynamically pre-
ferred to addition of CO2.
To gain additional insight into the different intrinsic
reactivity patterns of phenyl imido and hydrazido com-
plexes, we carried out DFT studies of various reaction
pathways. Figure 8 shows the computed reaction profile
for CpTi{MeC(NMe)2}(NNMe2) (1NMe2) with the three
model substrates CO2, CS2, and MeNCO (see below for
the corresponding experimental systems), comparing cy-
cloaddition, cycloaddition-insertion, and cycloaddi-
tion-extrusion possibilities. Examples of all three
pathways have been found for the hydrazides 13-15
(Scheme 1 and below) and previously for the imido com-
plexes 7 and 8.28,29,46 Figure 9 compares these same three
reaction outcomes for CO2 with CpTi{MeC(NMe)2}(NR),
where R = Ph (1Ph), NPh2 (1NPh2), NMe2 (1NMe2).
Figure 8 predicts that, in the absence of significant steric
repulsions, [2 þ 2] cycloaddition products of the type
2NMe2_Z should be stable for all three substrates, with
those formed from CS2 being the most thermodynamically
stable by 2.8 kcalmol-1. This is consistentwith eq 2. “Double
insertion” products modeled by 3NMe2_Z are thermo-
dynamically stable with regard to the cycloaddition products
for CO2 and MeNCO but unstable in the case of CS2, again
consistent with experiment. In contrast to 3NMe2_O and
3NMe2_N, where the {Ti(OC)2(NR)} ring is almost planar, as
in the crystal structures of 18 and 19 (Figure 7), 3NMe2_S is
puckered (see Table S5 in the Supporting Information). This
prevents electron donation from the sulfur LP to the metal,
destabilizing the overall molecule. With CO2 and MeNCO,
the activation barrier required for the second insertion is
around 14 kcalmol-1 higher than for the first one, explaining
the higher temperatures and reaction times normally re-
quired for the second insertion reaction. The barrier to
extrusion from 2NMe2_Z forming 4_X and Me2NNCO or
Me2NNCNMe is comparable to that for CO2 or MeNCO
insertion in the case of 2NMe2_O and 2NMe2_NMe, but the
elimination products are þ7.6 and þ9.9 kcal mol-1 less
stable thermodynamically. On the other hand, Me2NNCS
elimination from 2NMe2_S is only slightly thermodynami-
cally unfavorable (þ1.6 kcal mol-1), showing the possibility
for extrusion in the latter case. Interestingly, while both
2NMe2_O and 2NMe2_S are stable to extrusion, loss of
CO2 is the kinetically most accessible and thermodyamically
least unfavorable option for 2NMe2_O, whereas for
2NMe2_S, Me2NNCS extrusion is the least unfavored op-
tion and is slightly kinetically preferred.
Figure 9 compares the reaction profiles of the three model
systems 1Ph, 1NMe2, and 1NPh2 with CO2 as a representative
substrate.We have reported the profile for 1Ph (and that of the
Table 2. Selected Distances (A˚) and Angles (deg) for Cp*Ti-
{MeC(NiPr)2}{OC(O)N(NPh2)C(O)O} (18) and Cp*Ti{MeC-
(NiPr)2}{OC(O)N(NMe2)C(O)O} (19)
a
param 18 19
Ti(1)-Cpcent 2.051 2.053
Ti(1)-O(1) 1.9367(19) 1.9018(18)
Ti(1)-O(3) 1.9512(18) 1.9460(18)
Ti(1)-N(3) 2.059(2) 2.073(2)
Ti(1)-N(4) 2.090(2) 2.123(2)
C(1)-O(2) 1.206(3) 1.209(3)
C(2)-O(4) 1.218(3) 1.213(3)
N(1)-N(2) 1.394(3) 1.414(3)
Cpcent-Ti(1)-N(3) 117.3 120.1
Cpcent-Ti(1)-N(4) 111.9 114.3
Cpcent-Ti(1)-O(1) 114.3 114.5
Cpcent-Ti(1)-O(3) 109.5 108.7
N(3)-Ti(1)-N(4) 64.14(9) 63.79(9)
O(1)-Ti(1)-O(3) 82.99(8) 82.63(7)
Ti(1)-O(1)-C(1) 134.43(17) 136.84(16)
Ti(1)-O(3)-C(2) 131.98(16) 136.68(17)
C(1)-N(1)-C(2) 128.3(2) 126.6(2)
aCpcent is the computed Cp* ring carbon centroid.

1190 Organometallics, Vol. 30, No. 5, 2011 Tiong et al.
tert-butyl analogue CpTi{MeC(NMe)2}(N
tBu) (1tBu)) re-
cently as part of our detailed study of the reactions of imido
complexes 7 and 8withCO2.
29Herewe aremainly interested in
comparing the differences between hydrazides and imides, and
the effect of the N
β
substituents.
The cycloaddition products 2R_O are of similar energies
for all three systems, with addition to TidNNMe2 being
the most favorable. A low activation barrier is found for
all cases, although that for 1Ph is somewhat higher than for
the hydrazido systems, which are effectively identical.
The activation barrier for CO2 insertion to form 3R_O
is significantly higher for 2NPh2 (30.6 kcal mol
-1) than
for the others, consistent with the extended reaction
times needed to form 18 experimentally. Thermodynami-
cally, insertion is most favored for the hydrazide-derived
systems than for 2Ph_O. As for 2R_O hydrazide-derived
systems, the most stable 3R_O complex appears to be for
R = NMe2.
Figure 9. Gibbs free energy diagram (kcal mol-1) at 298 K for the CO2 cycloaddition and second CO2 insertion (solid lines) or
isocyanate extrusion (dotted lines) for the phenyl imido complex 1Ph (black lines) and its hydrazide analogues 1NPh2 (blue lines) and
1NMe2 (red lines).
Figure 8. Simplified Gibbs free energy diagram (kcal mol-1) at 298 K for the cycloaddition-insertion and cycloaddition-extrusion
reactions of CpTi{MeC(NMe)2}(NNMe2) (1NMe2) with CO2, CS2, and MeNCO. Note that Z = O, S in the case of CO2 and CS2,
respectively, and Z = N in the case of MeNCO. Some intermediates with CS2 and MeNCO have been omitted to facilitate the
comparison between the various substrates (see Figure 13 and Figure S2 in the Supporting Information).

Article Organometallics, Vol. 30, No. 5, 2011 1191
With regard to extrusion of RNCO from 2R_O, the
activation barriers increase in the order R = Ph < NMe2
< NPh2. In all cases the process is unfavorable but is least
prohibited for R = Ph and most disfavored for R = NPh2.
Figure 9 suggests that CO2 loss from the 2R_O hydrazide-
derived systems is less unfavorable both kinetically and
thermodynamically than RNCO elimination. In contrast,
CO2 and PhNCO elimination from 2Ph_O appear to be
equally kinetically feasible and thermodynamically disfa-
vored by a similar amount. We have previously shown that
the TolNCOmoiety in Cp*Ti{MeC(NiPr)2}{N(Tol)C(O)O}
(22) can be sequestered by added Ti(Me4taa)(O) as an
isocyanate trap.29 A comparison of Figures 8 and 9 offers
an explanation for the stability of the CS2 cycloaddition
products Cp*Ti{MeC(NiPr)2}{N(NR2)C(S)S} (20 and 21),
while the imido-derived analogues all eliminate RNCS. The
previously reported profile for 1tBu was similar to that for
1Ph, but the barrier to CO2 insertion from 2
tBu_O was very
high, while tBuNCO extrusion became thermodynamically
favorable by -2.3 kcal mol-1 due to steric repulsions.
We carried out additional NMR tube scale reactions as a
probe of Figures 8 and 9. Reaction of Cp*Ti{MeC(NiPr)2}-
{N(NPh2)C(O)O} (16) with Cp*Ti{MeC(N
iPr)2}(NNMe2)
(15) in C6D6 gave immediate conversion to Cp*Ti{MeC-
(NiPr)2}{N(NMe2)C(O)O} (17) and Cp*Ti{MeC(N
iPr)2}-
(NNPh2) (13). This is consistent with the low computed
barrier to CO2 extrusion from 2R_O and more thermody-
namically favorable cycloaddition of CO2 to TidNNMe2.
However, the corresponding reaction of 16 with the tolyl
imide Cp*Ti{MeC(NiPr)2}(NTol) (23) gave the unexpected
outcome summarized in Scheme 2 after heating at 60
C
(negligible reaction was observed at room temperature). The
potential products Cp*Ti{MeC(NiPr)2}{N(Tol)C(O)O}
(2246) and 13were not observed, and instead the μ-oxo dimer
1229,46 and the new compound Cp*Ti{MeC(NiPr)2}{N-
(NPh2)C(NTol)O} (24) were formed immediately in quanti-
tative yield. Compound 24 can be prepared independently
from 13 and TolNCO and is discussed later on.
Given that 24 can be formed from 13 and TolNCO, a
likely mechanism accounting for the formation of 12 and
24 is initial extrusion of CO2 from 16 to form 22, which is
not observed but is known to release TolNCO in the
presence of a suitable trap (see above29). Trapping of the
TolNCO released from 22 by 13 would lead to 24 and
monomeric Cp*Ti{MeC(NiPr)2}(O), which is unstable to
dimerization, forming 12. Consistent with this, we found
that an independently prepared sample of 22 reacted
immediately with 13 in C6D6, forming 24 and 12 in
quantitative yield.
In contrast to the facile transfer ofCO2 from 16 to 15, there
was no reaction between Cp*Ti{MeC(NiPr)2}{N(NPh2)C-
(S)S} (20) and 15 at room temperature.Heating to 60
Cgave
decomposition to a mixture containing the previously
reported46 μ-sulfido dimer [Cp*Ti{MeC(NiPr)2}(μ-S)]2 (25)
and a number of unknown products. Although this could
mean that addition of CS2 to TidNNPh2 is thermodynami-
cally more favorable than addition to TidNNMe2, it could
also represent a kinetic limitation, since the computed barrier
for CS2 extrusion from 2NMe2_S (25.4 kcal mol
-1) is
significantly higher than for CO2 extrusion from 2NMe2_O
(18.3 kcal mol-1).
The corresponding reaction starting from 21 and 13 as a
further attempt to test experimentally the thermodynamic
preferences for CS2 binding gave [Cp*Ti{MeC(N
iPr)2}(μ-
S)]2 (25) and a new compound formulated as Cp*Ti{MeC-
(NiPr)2}{N(NPh2)C(NNMe2)S} (26) on the basis of its
1H
and 13CNMR spectra (eq 3). Compound 26 is the cycloaddi-
tion product of 13 andMe2NNCS and is the analogue of the
fully characterized compounds Cp*Ti{MeC(NiPr)2}{N-
(NPh2)C(NAr)S} (Ar = Tol, Ar0 (2,6-C6H3
iPr2)) prepared
from 13 and ArNCS (see below). The formation of 26 is
consistent with the DFT prediction (Figure 8) that
Me2NNCS extrusion from 2NMe2_S is thermodynamically
less disfavored than CS2 extrusion while being equally
kinetically accessible.
Reactions of Cp*Ti{MeC(NiPr)2}(NNPh2) (13) with Iso-
cyanates and Isothiocyanates. The reactions of Cp*Ti{MeC-
(NiPr)2}(NNPh2) (13) and Cp*Ti{MeC(N
iPr)2}(NNMe2)
(15) with isocyanates differ significantly, depending on the
individual β-NR2 group, and are described in turn. Scheme 3
summarizes the reactions of 13with selected isocyanates and
isothiocyanates.
Scheme 2. Reaction of Cp*Ti{MeC(NiPr)2}{N(NPh2)C(O)O}
(16) with Cp*Ti{MeC(NiPr)2}(NTol) (23)

1192 Organometallics, Vol. 30, No. 5, 2011 Tiong et al.
Reaction of 13 with TolNCO or Ar0NCO at room tem-
perature in benzene gave the C1-symmetric ureate-type
cycloaddition products Cp*Ti{MeC(NiPr)2}{N(NPh2)C-
(NAr)O} (Ar = Tol (24), Ar0 (27)) as dark brown solids in
ca. 70% isolated yield. The corresponding reactions with
ArNCS afforded Cp*Ti{MeC(NiPr)2}{N(NPh2)C-
(NAr)S} (Ar = Tol (28), Ar0 (29)) as dark green solids
in slightly lower yields (ca. 50%), although the corre-
sponding NMR tube scale experiments for both ArNCO
and ArNCS were effectively quantitative. Diffraction-
quality crystals of 27 and 29 were grown by slow cooling
of a hexane solution, and the molecular structures and
selected distances and angles are shown in Figure 10 and
Table 3.
Figure 10 confirms the four-legged piano-stool geometries
around titaniumand the κ2N,Oand κ2N,S coordinationmodes
for the N(NPh2)C(NAr)E ligands (E = O, S). The NMR
spectra for 24 and 27-29 are consistent with the proposed
structures. No signals for other isomers of 24 and 27-29 (e.g.,
with a κ2N,N0-N(NPh2)C(E)NArmoiety) were observed in the
NMR tube scale experiments or crude reaction products.
Although they have not been crystallographically authenti-
cated, the tolyl-substituted analogues Cp*Ti{MeC(NiPr)2}{N-
(NPh2)C(NTol)E} (24 and 28) appear to have analogous
structures. For example, very similar ν(CdN) bands for 24
and 27 were observed at 1619 and 1622 cm-1, respectively,
which are also comparable to those for the imido-derived
products Cp*Ti{MeC(NiPr)2}{N(Ar
1)C(NAr2)O} (Ar1, Ar2
= Tol, 2,6-C6H3Me2, ν(CdN) 1609-1615 cm
-1), which pos-
sess κ2N,O-bound N(Ar1)C(NAr2)O groups. In contrast, the
IR spectrum of Ti(Me4taa){N(NPh2)C(O)NTol}, possessing a
κ
2N,N0-N(NPh2)C(O)NTol ligand, features a ν(CdO) band at
1656 cm-1.
The metric parameters for the Cp*Ti{MeC(NiPr)2} moiety
in 27 and 29 are within the expected ranges, and those for the
N(NPh2)C(NAr0)E ligands are comparable to the same groups
recently reported in Ti(N2N
Me){N(NPh2)C(NAr0)E}(L) (L=
py,E=O;L=none, E=S) which also feature κ2N,Oor κ2N,
S coordination.32 Interestingly, Gade et al. found that Cp*Ti-
(NXylN)(NNRPh)(L) (6;R=Ph,Me,L=tBuNH2,py) reacts
with PhNCOorPhNCS to give amixture of isomers possessing
either a κ2N,E or κ2N,N0 ureate ligand.37 An example of each
type was crystallographically characterized.
To probe further the coordination mode preferences in
24 and 27, we calculated the DFT energies of the model
complexes CpTi{MeC(NMe)2}{κN,O-N(NPh2)C(NPh)O}
(KN,O-2Ph_N) and CpTi{MeC(NMe)2{κN,N0-N-
(NPh2)C(O)NPh} (KN,N0-2Ph_N). Isomer KN,N0-2Ph_N
was found to be more stable, but by only 1 kcal mol-1.
Thus, as found in related systems, theN,N0-ureate systems
appear to be electronically preferred, but steric factors can
easily overturn this.32,46
Reaction of 13 with tBuNCO gave Cp*Ti{MeC(NiPr)2}-
{N(NPh2)C(N
tBu)O} (30; Scheme 3). While 30 slowly elim-
inates tBuNCNNPh2, forming the oxo dimer 12 (ca. 30%
after 4 days at room temperature), it is significantly more
stable than the corresponding products formed from Cp*Ti-
{MeC(NiPr)2}(NR) (R =
tBu (7), Tol (23)) which quantita-
tively eliminate tBuNCNR within 2-3 h.46 These observa-
tions are consistent with theDFT calculations in Figure 9 for
the cycloaddition-isocyanate extrusion reactions of 1Ph
and 1NPh2 with CO2.
We previously found that the imide-isocyanate cycload-
dition species Cp*Ti{MeC(NiPr)2}{N(Tol)C(NTol)O}
could form “double insertion” products on reaction with
CO2 or ArNCO (Ar = Tol, 2,6-C6H3Me2). In a similar
manner, Cp*Ti{MeC(NiPr)2}{N(Tol)C(O)O} (22) inserted
ArNCO into the Ti-N(Tol) bond to also give a cross-
coupled derivative.46 In contrast, treatment of Cp*Ti{MeC-
(NiPr)2}{N(NPh2)C(NTol)O} (24) with further TolNCO
either at room temperature or at 60
C gave no reaction.
The corresponding reaction of 24 with CO2 successfully but
slowly (4 days) formed the mixed TolNCO/CO2 “double
insertion” product Cp*Ti{MeC(NiPr)2}{OC(NTol)N-
(NPh2)C(O)O} (31). The IR spectrum of 31 shows strong
bands at 1699 and 1628 cm-1 attributed to ν(CdO) and
ν(CdN), consistent with the proposed structure.46 No reac-
tion was observed between the bulkier 27 and CO2. Com-
pound 31 is the analogue of the structurally authenticated
Cp*Ti{MeC(NiPr)2}{OC(O)N(NPh2)C(O)O} (18). Surpris-
ingly, an attempt to form 31 by reaction of Cp*Ti{MeC-
(NiPr)2}{N(NPh2)C(O)O} (16) with TolNCOgave amixture
of 24, 31, 18, and unreacted 16.
Reaction of the bulkier Cp*Ti{MeC(NiPr)2}{N(NPh2)C-
(NtBu)O} (30) with CO2 in C6D6 slowly led to
tBuNCO
extrusion and formation of 18 (Scheme 3). This reaction
Scheme 3. Reactions of Cp*Ti{MeC(NiPr)2}(NNPh2) (13) with
Isocyanates, Isothiocyanates, and CO2
a
aAr0 = 2,6-C6H3
iPr2.

Article Organometallics, Vol. 30, No. 5, 2011 1193
most likely proceeds via elimination of the isocyanate to form
13. The reaction of pure 13 with CO2 to form 18 is faster than
the reaction with 30, explaining why the cycloaddition inter-
mediate 16 is not observed in the reaction of 30. Addition of
TolNCO to 30 also led to loss of tBuNCO, immediately
forming 24. Reaction of Cp*Ti{MeC(NiPr)2}(NNMe2) (15)
with 30 in C6D6 gave quantitative formation of 13, the μ-oxo
compound 12, and tBuNCNNMe2, consistent with the reac-
tions of 15 with tBuNCO and Ar0NCO described below
(Scheme 4).
As mentioned, the reaction of 24 with CO2 to form 31
requires 4 days for completion (with NMR monitoring),
whereas the corresponding reaction for Cp*Ti{MeC-
(NiPr)2}{N(Tol)C(NTol)O} under comparable conditions
was complete within 10 min.46 These differences are again
consistent with Figure 9 by analogy with the significantly
higher TS for 2NPh2_O þ CO2 f 3NPh2_O compared to
2Ph_O þ CO2 f 3Ph_O.
Reactions of Cp*Ti{MeC(NiPr)2}(NNMe2) (15) with Iso-
cyanates. In contrast to the relatively well-behaved cycload-
dition chemistry of 13with RNCO and RNCS, the reactions
of 15 with these substrates are dominated by
cycloaddition-extrusion processes. The reactions of 15
with isocyanates are shown in Scheme 4. Initial studies of
the corresponding reactions with isothiocyanates led to
unstable complexes and/or mixtures and were not pur-
sued further.
Reaction of 15 with tBuNCO in C6D6 gave quantitative
conversion to the μ-oxo compound 12 and the previously
reported69,70 N-(dimethylamino)carbodiimide tBuNCNNMe2
(32). Amidocarbodiimides are not stable and are known
Figure 10. Displacement ellipsoid plots (25% probability) of (a) Cp*Ti{MeC(NiPr)2}{N(NPh2)C(NAr0)O} (27) and (b) Cp*Ti{MeC-
(NiPr)2}{N(NPh2)C(NAr0)S} (29). H atoms are omitted for clarity.
Table 3. Selected Bond Lengths (A˚) and Angles (deg) for Cp*Ti-
{MeC(NiPr)2}{N(NPh2)C(NAr0)O} (27) and Cp*Ti{MeC-
(NiPr)2}{N(NPh2)C(NAr0)S} (29)
a
paramb 27 29
Ti(1)-Cpcent 2.065 2.075
Ti(1)-N(1) 2.000(15) 2.0335(18)
Ti(1)-E(1) 2.0060(14) 2.4512(8)
Ti(1)-N(3) 2.1498(17) 2.171(3)
Ti(1)-N(4) 2.0526(18) 2.050(2)
N(1)-N(2) 1.400(2) 1.416(3)
C(13)-N(5) 1.286(3) 1.273(3)
E(1)-C(13) 1.337(2) 1.769(2)
Cpcent-Ti(1)-N(1) 126.4 128.3
Cpcent-Ti(1)-E(1) 110.5 107.8
Cpcent-Ti(1)-N(3) 112.3 111.9
Cpcent-Ti(1)-N(4) 119.0 119.6
N(3)-Ti(1)-N(4) 63.46(7) 62.63(10)
N(1)-Ti(1)-E(1) 65.60(6) 67.98(6)
Ti(1)-N(1)-C(13) 93.31(11) 105.94(14)
Ti(1)-E(1)-C(13) 94.72(11) 80.08(8)
N(1)-C(13)-E(1) 105.50(15) 105.58(15)
aCpcent is the computed Cp* ring carbon centroid.
bE = O, S for 27
and 29, respectively.
Scheme 4. Reactions of Cp*Ti{MeC(NiPr)2}(NNMe2) (15)with
Isocyanatesa
aAr0 = 2,6-C6H3
iPr2.
(70) Sarker, S.; Cooley, J. H.;Willett, R. D.; Rheingold, A. L. J. Org.
Chem. 1995, 60, 476.

1194 Organometallics, Vol. 30, No. 5, 2011 Tiong et al.
to dimerize. In the case of 32, the heterocyclic product
1,2,4-N(Me)2NC(N
tBu)N(tBu)C(NNMe2) (33) has been
crystallographically characterized.70 The instability of
the presumed cycloaddition intermediate Cp*Ti{MeC-
(NiPr)2}{N(NMe2)C(N
tBu)O} to extrusion contrasts
strongly with that of 30 and is reminiscent of the corre-
sponding reactions of Cp*Ti{MeC(NiPr)2}(NR) (R =
tBu (7), Tol (23)) mentioned above. The outcomes of
these reactions are consistent with the DFT calculations
in Figure 9 for extrusion of RNCO from 2R_O, which
become progressively more favored (both kinetically and
thermodynamically) in the order R = Ph > NMe2 >
NPh2.
The stoichiometric reaction of 15 with Ar0NCO gave a
mixture of products and unreacted starting hydrazide. Con-
ducting the reaction at 60
C and with 2 equiv of Ar0NCO
gave 12 and 1,2,4-N(Me)2NC(NAr0)N(Ar0)C(O) (34). When
it was conducted on the NMR tube scale in C6D6, the
conversion of 15 to the products was near-quantitative. On
scale-up, the white solid 34 could only be isolated in analy-
tically pure form by high vacuum (5  10-6 mbar) tube
sublimation, leading to an overall yield of 15%.
Diffraction-quality crystals of 34 were grown from a
concentrated hexane solution at -4
C. The molecular
structure is shown in Figure 11, and selected distances and
angles are given in Table S1 of the Supporting Information.
These are all within normal ranges71 and comparable to
those of 33.70 Compound 34 is the apparent product of
coupling between Ar0NCO and Ar0NCNNMe2, which is
not observed in the reaction mixture but is analogous to
tBuNCNNMe2 formed in the reaction of 15 with
tBuNCO.
Carbodiimide Ar0NCNNMe2 is probably formed by extru-
sion from the likely intermediate Cp*Ti{MeC(NiPr)2}
{N(NMe2)C(NAr0)O} (34_int), the analogue of the cry-
stallographically characterized 27 (Figure 10). The in-
corporation of both an Ar0NCO and Ar0NC fragment into
34 accounts for the 1:2 stoichiometry required for this
reaction.
The reaction of 15 with TolNCO also required 2 equiv of
the isocyanate for complete reaction (Scheme 4). However,
in this case the single reaction product was the “double-
insertion” compound Cp*Ti{MeC(NiPr)2}{OC(NNMe2)N-
(Tol)C(NTol)O} (35), isolated in 76% yield. Compound 35
has been crystallographically characterized, and the molec-
ular structure is shown in Figure 12. Selected distances and
angles are given in Table 4 and are within the expected
ranges. The 1H and 13C NMR spectra of 35 show two sets
of p-tolyl group resonances and two inequivalent isopropyl
groups for the MeC(NiPr)2 ligand. The IR spectrum shows
two ν(CdN) bands at 1619 and 1599 cm-1. Surprisingly, the
product is not the Cs-symmetric Cp*Ti{MeC(N
iPr)2}
{OC(NTol)N(NNMe2)C(NTol)O} (35_alt) which would be
expected on the basis of the reactions of Cp*Ti{MeC(N-
iPr)2}(NTol) with 2 equiv of TolNCO or Cp*Ti{MeC-
(NiPr)2}(NNR2) with an excess of CO2. The presence of both
an exocyclic CdNTol and CdNNMe2 moiety suggests that
at least one rearrangement must have taken place between
the likely intermediate Cp*Ti{MeC(NiPr)2}{N(NMe2)
Figure 11. Displacement ellipsoid plot (20% probability) of
1,2,4-N(Me)2NC(NAr0)N(Ar0)C(O) (34). H atoms are omitted
for clarity.
Figure 12. Displacement ellipsoid plot (20% probability) of
Cp*Ti{MeC(NiPr)2}{OC(NNMe2)N(Tol)C(NTol)O} (35). H
atoms are omitted for clarity.
Table 4. Selected Distances (A˚) and Angles (deg) for Cp*Ti-
{MeC(NiPr)2}{OC(NNMe2)N(Tol)C(NTol)O} (35)
a
Ti(1)-Cpcent 2.067 Ti(1)-O(2) 1.9359(17)
Ti(1)-N(3) 2.108(2) N(5)-C(5) 1.455(3)
Ti(1)-N(4) 2.077(2) C(3)-N(1) 1.289(3)
Ti(1)-O(1) 1.9065(17) C(4)-N(6) 1.288(3)
N(1)-N(2) 1.457(3)
Cpcent-Ti(1)-N(3) 110.9 Cpcent-Ti(1)-N(4) 114.6
Cpcent-Ti(1)-O(1) 116.1 Cpcent-Ti(1)-O(2) 111.0
N(3)-Ti(1)-N(4) 63.54(8) O(1)-Ti(1)-O(2) 83.63(7)
Ti(1)-O(1)-C(3) 134.38(15) Ti(1)-O(2)-C(4) 135.27(15)
C(3)-N(5)-C(4) 124.5(2)
aCpcent is the computed Cp* ring carbon centroid.
(71) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen,
A. G.; Taylor, R. J. Chem. Soc., Perkin Trans. 2 1987, S1.

Article Organometallics, Vol. 30, No. 5, 2011 1195
C(NAr)O} (35_int, the analogue of 24) and the final prod-
uct 35.
We have used DFT to study the mechanism of formation
of 35 using the model system CpTi{MeC(NMe)2}(NNMe2)
(1NMe2) andMeNCO (Figure 13). A part of this mechanism
was already included in Figure 8.Addition ofMeNCO forms
2NMe2_N with a κN,O-ureate ligand. Insertion of MeNCO
into the Ti-N(NMe2) bond of 2NMe2_N forms the sym-
metric “double insertion” product 3NMe2_N in a slightly
exergonic process (ΔG = -2.2 kcal mol-1). The TS for this
process lies 27.2 kcal mol-1 above 2NMe2_N. A more
accessible second MeNCO insertion was found via the
alternative N,O coordination isomer 2NMe2_N0, with an
exocyclic CdNNMe2 group. Direct rearrangement of
2NMe2_N to 2NMe2_N0 by effective rotation about the
O-CN2 bond has a prohibitively high TS of þ36.5 kcal
mol-1 relative to 2NMe2_N. However, extrusion of
MeNCNNMe2 from 2NMe2_N to form 4_O, followed
by recoordination and cycloaddition, presents an alter-
native route to 2NMe2_N0. Relative to 2NMe2_N, the
highest TS along this route is 23.5 kcal mol-1 (between
2NMe2_N_int0 and 2NMe2_N0), which is lower than the
27.2 kcal mol-1 between 2NMe2_N and 3NMe2_N. In-
sertion of MeNCO into the Ti-N(Me) of 2NMe2_N0
forms the desired isomer 3NMe2_N0 (a model of 35) with
an activation free energy barrier of þ20.7 kcal mol-1
relative to 2NMe2_N0. Note that 3NMe2_N0 is -3.1 kcal
mol-1 more stable than the more symmetrical isomer
3NMe2_N and so represents both the thermodynamic
and kinetically favored product.
In principle, this model mechanism could apply to TolN-
CO, tBuNCO, or Ar0NCO, whereas in practice different
outcomes are found for each isocyanate. These reflect the
different steric bulk of each of the isocyanates and their
Figure 13. DFT mechanism for the formation of CpTi{MeC(NMe)2}{OC(NNMe2)N(Me)C(NMe)O} (3NMe2_N0). Gibbs free
energies (298 K) are expressed in kcal mol-1 relative to 1NMe2 þ 2 MeNCO. The “first” MeNCO is colored blue and the “second”
in red for clarity. All energies are shown in boxes; the values labeled q are transition states.

1196 Organometallics, Vol. 30, No. 5, 2011 Tiong et al.
relative rates of RNCNNMe2 being trapped back by
Cp*Ti{MeC(NiPr)2}(O) (seen for R = Tol), free RNCO
in the reaction mixture (R = Ar0), or not at all (R0 = tBu).
Further Thermodynamic Considerations. Although many
reactions of Cp*Ti{MeC(NiPr)2}(NR) (R =
tBu (7), Tol
(23), NNPh2 (13), NNMe2 (15)) and their homologues with
heterocumulenes can result in isolable cycloaddition or
“double-insertion” products, there is also a propensity to
undergo an overall cycloaddition/extrusion process whereby
the “NR” group is transferred to an organic fragment, itself
being replaced by O or S. We have shown previously,
through DFT and experimental studies, that increased steric
bulk of the cyclopentadienyl-amidinate ligand set can ki-
netically stabilize cycloaddition products toward extrusion.
We also showed that the steric demands of the tBu group in
tert-butyl imido complexes leads to extrusion becoming
thermodynamically more favorable.29,46 The DFT com-
puted reaction of the model imido complex CpTi{MeC-
(NMe)2}(NMe) (1Me) with CO2 to form CpTi{Me-
C(NMe)2}(O) (4_O) and MeNCO was found to be 5.7 kcal
mol-1 more favorable (in terms of ΔE) than the correspond-
ing reaction of 1Ph with CO2 to form PhNCO, showing a
clear underlying preference for NR group transfer to CO in
the case of NMe compared to NPh.
In this contribution, we have extended the experimental
and DFT information for this type of reactivity to include
NNMe2 and NNPh2 ligands for the three main substrate
classes (CO2, CS2, and isocyanates) studied previously with
the imido complexes 7 and 23. Overall, as demonstrated by
experiment and DFT (cf. Figure 9), the tendency to transfer
an imido or hydrazido group from titanium to an organic
fragment (CO, CS, CNR) appears to increase in the order
NNPh2 < NNMe2 < NTol (<N
tBu). Additionally, taking
into account the new results above and those described
previously for 7 and 23, the imido or hydrazide group
exchange occurs more readily with CS2 than with isocya-
nates, which in turn are less likely thanCO2 to give an overall
metathesis reaction (cf. Figure 8).
Figure 14. Energy decomposition scheme for selected isodesmic multiple bond exchange reactions of CpTi{MeC(NMe)2}(NR) (R=
Me, Ph, NPh2, NMe2) with heterocumulenes and computed bond dissociation energies (ΔE, kcal mol
-1). All species are spin state
singlets except for the fragments CpTi{MeC(NMe)2}, X, NMe, and NPh, which are spin triplets. ΔEexch = ΔE1 þ ΔE2 - ΔE3 - ΔE4.

Article Organometallics, Vol. 30, No. 5, 2011 1197
To gain further insight into the underlying factors in
these metathesis processes, we have analyzed the model
thermodynamic cycle in Figure 14, in which TidNR of
1Me, 1Ph, 1NPh2, or 1NMe2 exchanges with CdX (X=O,
S) of CO2, MeNCO, or CS2. The overall energy of this
exchange (ΔEexch) can be expressed as the sum of four
stepwise ond dissociation energies (BDEs) or the reverse
processes: ΔE1 (TidNR homolysis), ΔE2 (substrate CdX
homolysis), -ΔE3 (TidX formation), and -ΔE4 (product
CdNR
bond formation). This allows us to assess the effects of the
relative affinities of the metal and organic fragment
for the NR or X groups and their overall impact on ΔEexch.
72
The computed BDEs for the hydrazides 1NMe2 and
1NNPh2 (entries 1 and 2) are between 23.9 and 33.1 kcal
mol-1 less than for the imides 1Ph and 1Me (entries 3 and 4).
The TidNNMe2 BDE is somewhat less than that of
TidNNPh2 (8.7 kcal mol
-1). The bond energies of TidO
and TidS (entries 8 and 9) are both greater than those of any
of the TidNR systems. Therefore, in terms of tita-
nium-ligand bond strengths, the metathesis reaction is al-
ways favorable, and more so for the hydrazides than the
imides and for oxide than sulfide bond formation. However,
the experimental results reported above and previously,29,46
along with Figures 8 and 9, are not consistent with these
expectations based on titanium-ligand bond strengths alone.
The substrate and product bond energies also play a key role.
Comparison of entries 1-4 (TidNR BDEs) with entries
10-13 (OCdNR BDEs) or 14-17 (SCdNR BDEs) show
that these all increase in the order NR=NNMe2 <NNPh2
< NPh < NMe. However, the magnitudes of the changes
(i.e., the relative affinities of NR for Ti, CO, or CS) differ, and
this accounts for the different propensities for TidNR/CdO
or CdSmetathesis in the real systems. Consider, for example,
the reactions with CO2. Although the BDE for OCdNNPh2
(entry 11) is 2.8 kcal mol-1 greater than for OCdNNMe2
(entry 10), that for TidNNPh2 is 8.7 kcal mol
-1 greater than
that for TidNNMe2. Overall, therefore, exchange of
TidNNR2 and OCdO forming TidO and OC=NNR2 is
5.9 kcal mol-1 more favorable for NNR2 = NNMe2. Like-
wise, exchange between TidNNR2 and MeNCdO forming
TidOandMeNCdNNR2 is 4.0 kcalmol
-1more favorable for
NNR2 = NNMe2 (compare entries 1, 2 and 18, 19), which is
consistent with experimental trends.
On comparison of phenyl imido and hydrazido systems,
entries 2 and 3 show that theTidNPhBDE is 23.9 kcalmol-1
greater than for TidNNPh2, whereasNPh transfer reactions
are more favored. This is explained by comparing the BDEs
forOCdNNPh2 andOCdNPh (entries 11 and 12), which are
greater by 35.6 kcal mol-1 for NPh. Thus, TidNPh/OCdO
metathesis is favored by 11.7 kcal mol-1 compared to
TidNNPh2 because of the greater affinity of NPh for CO.
Similarly, TidNPh/SCdS metathesis is favored by 9.8 kcal
mol-1 compared to the same process for TidNNPh2 (com-
pare entries 2, 3 and 15, 16), again consistent with experi-
mental observations of ready formation of sulfide products
in the reactions of aryl imido compounds with CS2 but stable
cycloaddition products with 13 and 15. Finally, it should be
noted that the calculated energy for TidNNMe2 þ CO2 f
TidO þ OCNNMe2 (8.4 kcal mol
-1) is significantly higher
than the corresponding process for MeNCO forming
MeNCNNMe2 (2.7 kcal mol
-1), consistent with the
observed behavior of the real system 15 with CO2 and
isocyanates.
Conclusions
The cyclopentadienyl-amidinate complexes Cp*Ti-
{MeC(NiPr)2}(NNR
1R2) (R1 = Ph, R2 = Ph (13), Me
(14); R1 =R2 =Me (15)) have allowed a detailed combined
experimental andDFT study of terminal titanium hydrazido
complexes as a function of the N
β
substituents. Compounds
13-15 permitted the second crystallographic comparison of
a series of this type. DFT studies of the model analogues
CpTi{MeC(NMe)2}(NNR
1R2) confirmed the overall struc-
tural trends and an explanation in terms of the effects of the
N
β
lone pair. A comparison with the corresponding model
imido complexes CpTi{MeC(NMe)2}(NR) (R = Me, Ph)
completed the bonding picture.
Compounds 13 and 15 can have different reactivities at the
TidN
R
bond (cycloaddition, cycloaddition-insertion, cy-
cloaddition-elimination), depending on the N
β
substituents
and the substrates in question. With CO2 and CS2, the
chemistry is generally rather similar, and reaction products
of the type seen previously with imido compounds Cp*Ti-
{MeC(NiPr)2}(NR) (R =
tBu (7), Tol (23)) were observed.
The cycloaddition products formed with the hydrazides
were, however, more stable with regard to extrusion reac-
tions. In the reactions of 13 and 15 with tBuNCO, TolNCO,
and Ar0NCO there was a more clear-cut difference in reac-
tions. The diphenyl hydrazido compound 13 formed quite
stable cycloaddition products, which in the case of Cp*Ti-
{MeC(NiPr)2}{N(NPh2)C(NTol)O} reacted further with
CO2 to give a mixed cycloaddition-insertion product. With
15 the chemistry was more dominated by cycloaddition-
elimination reactions. Reaction with tBuNCOorAr0NCO (2
equiv) gave tBuNCNNMe2 or the heterocycle 1,2,4-N-
(Me)2NC(NAr0)N(Ar0)C(O), respectively, along with
[Cp*Ti{MeC(NiPr)2}(μ-O)]2. With TolNCO (2 equiv),
Cp*Ti{MeC(NiPr)2}{OC(NNMe2)N(Tol)C(NTol)O} was
formed via a series of cycloaddition-elimination and cy-
cloaddition-insertion steps.
The energetics and mechanisms of the cycloaddition,
cycloaddition-insertion, and cycloaddition-extrusion pro-
cesses of variousmodel imido and hydrazido complexes were
investigated using DFT. In the latter (metathesis) reactions,
the reaction outcomes depend on a delicate balance of the
relative affinities of NR or NNR2 for the metal center or the
organic fragment (CO, CS, or RNC).
Experimental Section
General Methods and Instrumentation. All manipulations
were carried out using standard Schlenk line or drybox techni-
ques under an atmosphere of argon or dinitrogen. Solvents were
degassed by sparging with dinitrogen and dried by passing
through a column of the appropriate drying agent.73 Deuterated
solvents were refluxed over the appropriate drying agent, dis-
tilled, and stored under dinitrogen in Teflon valve ampules.
NMR samples were prepared under dinitrogen in 5mmWilmad
507-PP tubes fitted with J. Young Teflon valves. 1H and 13C-
{1H} NMR spectra were recorded on Varian Mercury-VX 300
(72) Note that Figure 14 presents electronic energies using
6-311þþG** basis sets, whereas Figures 8 and 9 present Gibbs free
energies using a 6-31G** basis set.
(73) Pangborn,A. B.;Giardello,M.A.; Grubbs, R.H.; Rosen,R.K.;
Timmers, F. J. Organometallics 1996, 15, 1518.

1198 Organometallics, Vol. 30, No. 5, 2011 Tiong et al.
and Varian Unity Plus 500 spectrometers and referenced internally
to residual protio solvent (1H) or solvent (13C) resonances and are
reported relative to tetramethylsilane (δ 0 ppm). Assignments were
confirmed as necessary with the use of DEPT-135, DEPT-90, and
two-dimensional 1H-1H and 13C-1H NMR correlation experi-
ments. Chemical shifts are quoted in δ (ppm) and coupling
constants in Hz. IR spectra were recorded on a Nicolet Magna
560ESPFTIR spectrometer. Sampleswere prepared in a drybox as
Nujol mulls between NaCl plates, and the data are quoted in
wavenumbers (cm-1). Mass spectra were recorded by the mass
spectrometry service of Oxford University’s Department of Chem-
istry.Elemental analyseswere carriedoutby theElementalAnalysis
Service at the London Metropolitan University.
Starting Materials. Cp*Ti{MeC(NiPr)2}(N
tBu) (7),46 Cp*Ti-
{MeC(NiPr)2}(NTol) (23),
46 and Cp*Ti{MeC(NiPr)2}{N(Tol)C-
(O)O} (22)46 were prepared according to the literature methods.
1,1-Diphenylhydrazine was obtained from Sigma-Aldrich as the
hydrogen chloride salt, fromwhich the freehydrazinewasobtained
by basification, drying, and removal of residual solvent, followed
by distillation under inert atmospheric conditions. 1,1-Dimethyl-
hydrazine and 1-methyl-1-phenylhydrazine and pyridine were
dried over freshly ground CaH2 and distilled before use. Other
reagents were obtained commercially and used as received.
Representative syntheses and associated characterization data
are listed below.Details of the remaining syntheses, NMR spectra,
and characterizationdata are given in the Supporting Information.
Cp*Ti{MeC(NiPr)2}(NNPh2) (13). To a stirred red solution
of Cp*Ti{MeC(NiPr)2}(N
tBu) (7; 1.70 g, 4.30 mmol) in benzene
(10 mL) was added Ph2NNH2 (0.140 g, 0.760 mmol) in benzene
(10mL). The solution darkened, and after 16 h the volatiles were
removed under reduced pressure. The resultant solid was ex-
tracted into pentane (3  10 mL) and filtered, and the volatiles
were removed under reduced pressure to give 13 as a dark yellow
solid. Yield: 1.81 g (83%). Diffraction-quality crystals were
grown by slow cooling of a saturated pentane solution. 1H
NMR (C6D6, 299.9 MHz, 293 K): δ 7.22 (4 H, d,
3J = 8.8 Hz,
o-C6H5), 7.13 (4 H, dd,
3J=7.5 and 8.8 Hz,m-C6H5), 6.81 (2 H,
t, 3J = 7.5 Hz, p-C6H5), 3.60 (2 H, app sept, app
3J = 6.3 Hz,
NCHMeMe), 1.99 (15 H, s, C5Me5), 1.65 (3 H, s, MeCN2), 1.04
(6 H, d, 3J = 6.3 Hz, NCHMeMe), 1.03 (6 H, d, 3J = 6.3,
NCHMeMe). 13C{1H}NMR (C6D6, 75.4MHz, 293K): δ 160.7
(MeCN2), 147.1 (i-C6H5), 129.1 (m-C6H5), 122.0 (p-C6H5),
120.6 (o-C6H5), 120.0 (C5Me5), 49.5 (NCHMeMe), 26.8
(NCHMeMe), 25.8 (NCHMeMe), 12.7 (C5Me5), 12.3
(MeCN2). IR (NaCl plates, Nujol mull, cm
-1): ν 1595 (m),
1586 (m), 1488 (s), 1465 (s), 1417 (w), 1378 (m), 1364 (s), 1340
(w), 1320 (w), 1295 (w), 1277 (w), 1254 (w), 1215 (m), 1169 (m),
1148 (w), 1119 (w), 1070 (w), 1026 (w), 992 (w), 839 (w), 812 (w),
792 (w), 751 (w), 741 (s), 701 (w), 693 (s), 666 (w), 631 (m). Anal.
Found (calcd for C30H42N4Ti): C, 71.0 (71.1); H, 8.3 (8.4); N,
11.0 (11.1).
Cp*Ti{MeC(NiPr)2}{N(NPh2)C(O)O} (16). A solution of
Cp*Ti{MeC(NiPr)2}(NNPh2) (13; 0.300 g, 0.590 mmol) in
toluene (20 mL) was freeze-pump-thawed three times. The
solution was then exposed to CO2 at a pressure of ca. 1.1 atm at
-78
C. Immediately after the color changed from dark yellow
to dark brown, the excess CO2 and the other volatiles were
removed under reduced pressure to afford 16 as a dark brown
solid. The resultant dark brown solid was washed with cold
pentane (3  5 mL), filtered, and dried in vacuo. Yield: 0.175 g
(54%). 1HNMR (C7D8, 499.9MHz, 293K): δ 7.51 (2H, d,
3J=
7.0 Hz, oa-C6H5), 7.19 (2 H, m, ma-C6H5), 6.95 (4 H, m, over-
lapping ob-C6H5 and mb-C6H5), 6.91 (1 H, t,
3J = 7.0 Hz, pa-
C6H5), 6.73 (1 H, t,
3J = 7.0 Hz, pb-C6H5), 3.31 (1 H, app sept,
app 3J = 6.5 Hz, NCHaMeMe), 2.83 (1 H, app sept, app
3J =
6.5 Hz, NCHbMeMe), 1.95 (15 H, s, C5Me5), 1.46 (3 H, s,
MeCN2), 1.16 (3 H, d,
3J=6.5 Hz, NCHaMeMe), 1.11 (3 H, d,
3J = 6.5 Hz, NCHbMeMe), 1.09 (3 H, d,
3J = 6.5 Hz,
NCHaMeMe), 0.93 (3 H, d,
3J = 6.5 Hz, NCHbMeMe).
13C-
{1H}NMR (C7D8, 125.7MHz, 293 K): δ 170.3 (MeCN2), 160.6
(OC(O)N), 147.9 (ia-C6H5), 147.9 (ib-C6H5), 130.4 (C5Me5),
128.5 (ma-C6H5, mb-C6H5), 122.8 (pa-C6H5), 122.4 (oa-C6H5),
119.6 (pb-C6H5), 117.0 (ob-C6H5), 51.2 (NCHaMeMe), 50.2
(NCHbMeMe), 26.3 (NCHbMeMe), 24.6 (NCHbMeMe), 24.2
(NCHaMeMe), 24.1 (NCHaMeMe), 12.9 (C5Me5), 12.6
(MeCN2). IR (NaCl plates, Nujol mull, cm
-1): ν 1684 (s),
1589 (m), 1492 (s), 1338 (m), 1206 (w), 1026 (w), 744 (m), 691
(m). EI-MS: m/z 233 [M - C5Me5 - N(NPh2)]
þ (30%), Anal.
Found (calcd for C31H42N4O2Ti): C, 67.61 (67.63); H, 7.78
(7.69); N, 10.11 (10.18).
Cp*Ti{MeC(NiPr)2}{OC(O)N(NPh2)C(O)O} (18). A solu-
tion of Cp*Ti{MeC(NiPr)2}(NNPh2) (13; 0.300 g, 0.590 mmol)
in toluene (20 mL) was freeze-pump-thawed three times. The
solution was then exposed to CO2 at a pressure of ca. 1.1 atm at
room temperature. An immediate color change from dark
yellow to dark brown was observed. After 3 days, excess CO2
and the other volatiles were removed under reduced pressure to
afford 18 as a dark brown solid. The resultant dark brown solid
was washed with cold pentane (3 5 mL), filtered, and dried in
vacuo. Yield: 0.247 g (70%). Diffraction-quality crystals were
grown by slow evaporation of an ether solution. 1H NMR
(C6D6, 299.9 MHz, 293 K): δ 7.88 (2 H, d,
3J = 7.2 Hz, oa-
C6H5), 7.27 (2H,m, ob-C6H5), 7.24 (2H,m,ma-C6H5), 7.09 (2H,
m,mb-C6H5), 6.98 (1 H, t,
3J=7.2Hz, pb-C6H5), 6.78 (1 H, t,
3J
= 7.2 Hz, pa-C6H5), 3.42 (2 H, app sept, app
3J = 6.6 Hz,
NCHMeMe), 1.87 (15 H, s, C5Me5), 1.39 (3 H, s, MeCN2), 1.05
(12 H, overlapping 2  d, 3J = 6.6 Hz, NCHMeMe,
NCHMeMe). 13C{1H} NMR (C6D6, 75.4 MHz, 293 K): δ
169.5 (MeCN2), 152.7 (OC(O)N), 146.7 (ib-C6H5), 146.0 (ia-
C6H5), 131.6 (C5Me5), 129.2 (ma-C6H5), 129.0 (mb-C6H5), 123.9
(pa-C6H5), 123.5 (oa-C6H5), 120.9 (pb-C6H5), 117.4 (ob-C6H5),
50.6 (NCHMeMe), 24.1 (NCHMeMe), 23.5 (NCHMeMe), 14.3
(MeCN2), 12.7 (C5Me5). IR (NaCl plates, Nujol mull, cm
-1): ν
2205 (w), 1715 (s), 1676 (s), 1590 (m), 1496 (s), 1365 (s), 1330 (s),
1209 (m), 1174 (m), 1122 (m), 1030 (w), 925 (w), 794 (m), 745
(m), 691 (m), 671 (w), 623 (w). EI-MS: m/z 459 [M - C5Me5]
þ
(10%), 426 [M - NPh2]
þ (10%). Anal. Found (calcd for
C32H42N4O4Ti): C, 64.58 (64.64); H, 7.14 (7.12); N, 9.37 (9.42).
NMR Tube Scale Reaction of Cp*Ti{MeC(NiPr)2}{N-
(NPh2)C(O)O} (16) with CO2. A 10.0 mg portion (0.018 mmol)
of Cp*Ti{MeC(NiPr)2}{N(NPh2)C(O)O} (16) was dissolved in
C6D6 (0.6mL), and and the solution was freeze-pump-thawed
three times. The solution was then exposed to CO2 at a pressure
of ca. 1.1 atm at room temperature. The reaction wasmonitored
by 1H NMR spectroscopy. The 1H NMR spectrum recorded
after 3 days showed quantitative formation of Cp*Ti{MeC-
(NiPr)2}{OC(O)N(NPh2)C(O)O} (18).
Cp*Ti{MeC(NiPr)2}{N(NPh2)C(S)S} (20). To a solution of
Cp*Ti{MeC(NiPr)2}(NNPh2) (13, 0.300 g, 0.590 mmol) in
benzene (20 mL) was added an excess of CS2 (0.107 mL, 1.78
mmol), all at room temperature. The resulting dark brown
solution was stirred for 16 h. Volatiles were then removed under
reduced pressure to afford 20 as a dark brown solid. The
resultant dark brown solid was washed with cold pentane (3 
5 mL), filtered, and dried in vacuo. Yield: 0.245 g (71%). 1H
NMR (C7D8, 499.9MHz, 263K): δ 7.47 (4 H, d,
3J=6.5Hz, o-
C6H5), 7.18 (4 H, t,
3J=6.5 Hz,m-C6H5), 6.90 (2 H, t,
3J=6.5
Hz, p-C6H5), 3.34 (1 H, app sept, app
3J = 6.5 Hz,
NCHaMeMe), 3.17 (1 H, app sept, app
3J = 6.5 Hz,
NCHbMeMe), 1.91 (15 H, s, C5Me5), 1.46 (3 H, s, MeCN2),
1.10 (3 H, d, 3J = 6.5 Hz, NCHaMeMe), 1.04 (3 H, d,
3J = 6.5
Hz, NCHaMeMe), 0.90 (3 H, d,
3J = 6.5 Hz, NCHbMeMe),
0.86 (3 H, d, 3J=6.5Hz, NCHbMeMe).
13C{1H}NMR (C7D8,
125.7 MHz, 263 K): δ 166.3 (MeCN2), 149.1 (overlapping i-
C6H5 and SC(S)N), 131.0 (C5Me5), 128.6 (m-C6H5), 121.6
(overlapping o- and p-C6H5), 50.9 (overlapping NCHaMeMe
and NCHbMeMe), 24.7 (NCHaMeMe), 24.2 (overlapping
NCHaMeMe and NCHbMeMe), 24.0 (NCHbMeMe), 13.8
(C5Me5), 13.3 (MeCN2). IR (NaCl plates, Nujol mull, cm
-1):
ν 1587 (s), 1491 (s), 1401 (m), 1333 (m), 1310 (m), 1276 (m), 1203

Article Organometallics, Vol. 30, No. 5, 2011 1199
(s), 750 (m), 603 (m). EI-MS: m/z 279 [M - C5Me5 - NPh2]
þ
(10%). Anal. Found (calcd for C31H42N4S2Ti): C, 63.88 (63.90);
H, 7.40 (7.27); N, 9.55 (9.62).
NMR Tube Scale Reaction of Cp*Ti{MeC(NiPr)2}(NNPh2)
(13) with Cp*Ti{MeC(NiPr)2}{N(NMe2)C(S)S} (21). To a solu-
tion of Cp*Ti{MeC(NiPr)2}{N(NMe2)C(S)S} (21; 0.012 g,
0.026 mmol) in C6D6 (0.3 mL) in an NMR tube equipped with
a J. Young Teflon valve was added Cp*Ti{MeC(NiPr)2}-
(NNPh2) (13; 0.013 g, 0.026 mmol) in C6D6 (0.3 mL) at room
temperature. The reaction was monitored by 1H NMR spec-
troscopy. [Cp*Ti{MeC(NiPr)2}(μ-S)]2 (25) and Cp*Ti{MeC-
(NiPr)2}{N(NPh2)C(NNMe2)S} (26) were formed quantita-
tively after 4 days. 26 was characterized by 1H NMR spectros-
copy. 1H NMR data (C6D6, 499.9 MHz, 293 K): δ 7.52 (1 H, d,
3J=7.5 Hz, oa-C6H5), 7.30 (1 H, d,
3J=7.5Hz, ob-C6H5), 7.21
(2 H, app t, app 3J=7.5Hz,ma-C6H5), 7.10 (2 H, app t, app
3J=
7.5 Hz, mb-C6H5), 6.88 (2 H, t,
3J = 7.5 Hz, pa-C6H5), 6.79 (2
H, t, 3J=7.5 Hz, pb-C6H5), 3.29 (1 H, app sept, app
3J=6.5 Hz,
NCHaMeMe), 2.97 (1 H, app sept, app
3J = 6.5 Hz,
NCHbMeMe), 2.51 (6 H, s, NNMe2), 1.96 (15 H, s, C5Me5),
1.50 (3 H, s, MeCN2), 1.20 (6 H, overlapping 2 d,
3J = 6.5 Hz,
overlapping NCHaMeMe and NCHbMeMe), 1.17 (3 H, d,
3J =
6.5 Hz, NCHaMeMe), 0.83 (3 H, d,
3J = 6.5 Hz, NCHbMeMe).
13C{1H} NMR (C6D6, 125.7 MHz, 293 K): δ 168.7 (MeCN2),
156.0 (SC(N)N), 147.4 (ia-C6H5) 147.4 (ib-C6H5), 129.2 (C5Me5),
128.3 (ma-C6H5), 128.1 (mb-C6H5), 121.7 (pa-C6H5), 121.3 (oa-
C6H5), 119.4 (pb-C6H5), 117.7 (ob-C6H5), 51.6 (NCHaMeMe), 49.4
(NCHbMeMe), 48.7 (NNMe2), 26.3 (NCHbMeMe), 25.5
(NCHbMeMe), 24.6 (NCHaMeMe), 23.5 (NCHaMeMe), 14.2
(MeCN2), 13.5 (C5Me5).
Cp*Ti{MeC(NiPr)2}{N(NPh2)C(NTol)O} (24).To a solution
of Cp*Ti{MeC(NiPr)2}(NNPh2) (13; 0.400 g, 0.790 mmol) in
benzene (20mL)was added p-TolNCO (0.100mL, 0.790mmol),
all at room temperature. An immediate color change from dark
yellow to dark brown was observed. After 16 h, the volatiles
were removed under reduced pressure to afford 24 as a dark
brown solid. The resultant dark brown solid was washed with
cold pentane (3  5 mL), filtered, and dried in vacuo. Yield:
0.342 g (68%). 1HNMR (C6D6, 299.9MHz, 293K): δ 7.71 (2H,
d, 3J=7.5Hz, oa-C6H5), 7.65 (2 H, d,
3J=7.5Hz, o-C6H4Me),
7.20 (2 H, t, 3J = 7.5 Hz, ma-C6H5), 7.10 (4 H, m, overlapping
ob-C6H5 and m-C6H4Me), 7.02 (2 H, t,
3J = 7.5 Hz, mb-C6H5),
6.90 (1 H, t, 3J=7.5 Hz, pa-C6H5), 6.74 (1 H, t,
3J=7.5Hz, pb-
C6H5), 3.29 (1 H, app sept, app
3J=6.5Hz, NCHaMeMe), 2.82
(1 H, app sept, app 3J = 6.5 Hz, NCHbMeMe), 2.18 (3 H, s,
C6H4Me), 1.96 (15 H, s, C5Me5), 1.40 (3 H, s, MeCN2), 1.17 (3
H, d, 3J = 6.5 Hz, NCHbMeMe), 1.11 (6 H, overlapping 2  d,
3J=6.5 Hz, overlapping NCHaMeMe and NCHaMeMe), 0.93
(3 H, d, 3J=6.5Hz, NCHbMeMe).
13C{1H} NMR (C6D6, 75.4
MHz, 293 K): δ 169.4 (MeCN2), 155.9 (OC(N)N), 147.7
(overlapping ia-C6H5 and ib-C6H5), 147.2 (i-C6H4Me), 129.7
(p-C6H4Me), 129.6 (C5Me5), 129.0 (m-C6H4Me), 128.7 (ma-
C6H5), 128.4 (mb-C6H5), 125.8 (o-C6H4Me), 122.41 (pa-C6H5),
122.2 (oa-C6H5), 119.3 (pb-C6H5), 117.2 (ob-C6H5), 50.9
(NCHaMeMe), 49.9 (NCHbMeMe), 26.3 (NCHbMeMe), 24.8
(NCHbMeMe), 24.4 (NCHaMeMe), 24.2 (NCHaMeMe), 21.0
(C6H4Me), 12.9 (C5Me5), 12.7 (MeCN2). IR (NaCl plates,Nujol
mull, cm-1): ν 1619 (m), 1587 (s), 1491 (s), 1336 (m), 1315 (m),
1206 (m), 1173 (w), 1124 (w), 1027 (w), 982 (w), 811 (w), 743 (m),
691 (w). EI-MS: m/z 506 [M - OC(NTol)]þ (20%). A satisfac-
tory elemental analysis could not be obtained.
Cp*Ti{MeC(NiPr)2}{N(NPh2)C(NTol)S} (28). To a solution
of Cp*Ti{MeC(NiPr)2}(NNPh2) (13; 0.300 g, 0.590 mmol) in
benzene (15mL) was added p-TolNCS (88.0 mg, 0.590mmol) in
benzene (15 mL), all at room temperature. The resulting dark
green solution was stirred for 16 h. Volatiles were then removed
under reduced pressure to afford 28 as a dark green solid. The
resultant dark green solid was washed with cold pentane (3  5
mL), filtered, anddried in vacuo.Yield: 0.210 g (54%). 1HNMR
(C6D6, 299.9 MHz, 293 K): δ 7.57 (2 H, d,
3J = 7.5 Hz, oa-
C6H5), 7.36 (2 H, d,
3J=7.5 Hz, ob-C6H5), 7.21 (2H, t,
3J=7.5
Hz, ma-C6H5), 7.12 (4 H, m, overlapping mb-C6H5 and m-
C6H4Me), 6.97 (2 H, d,
3J = 8.4 Hz, o-C6H4Me), 6.89 (1 H, t,
3J=7.5 Hz, pa-C6H5), 6.79 (1 H, t,
3J=7.5 Hz, pb-C6H5), 3.25
(1 H, app sept, app 3J = 6.6 Hz, NCHaMeMe), 2.98 (1 H, app
sept, app 3J = 6.6 Hz, NCHbMeMe), 2.08 (3 H, s, C6H4Me),
1.94 (15 H, s, C5Me5), 1.51 (3 H, s, MeCN2), 1.21 (6 H, over-
lapping 2  d, 3J = 6.6 Hz, overlapping NCHaMeMe and
NCHbMeMe), 1.10 (3 H, d,
3J=6.6 Hz, NCHaMeMe), 0.97 (3
H, d, 3J = 6.6 Hz, NCHbMeMe).
13C{1H} NMR (C6D6, 75.4
MHz, 293 K): δ 169.1 (MeCN2), 154.7 (SC(N)N), 147.5
(overlapping ia-C6H5, ib-C6H5 and i-C6H4Me), 130.9 (p-
C6H4Me), 129.8 (C5Me5), 129.0 (o-C6H4Me), 128.5 (ma-
C6H5), 123.7 (overlapping m-C6H4Me and mb-C6H5), 121.9
(pa-C6H5), 121.4 (oa-C6H5), 119.5 (pb-C6H5), 117.7 (ob-C6H5),
51.9 (NCHaMeMe), 49.6 (NCHbMeMe), 26.3 (NCHbMeMe),
25.5 (NCHbMeMe), 24.6 (NCHaMeMe), 23.5 (NCHaMeMe),
20.9 (C6H4 Me), 14.2 (MeCN2), 13.6 (C5Me5). IR (NaCl plates,
Nujol mull, cm-1): ν 1577 (s), 1490 (s), 1412 (m), 1327 (m), 1313
(m), 1278 (m), 1204 (m), 1167 (m), 1153 (m), 1104 (m), 1042 (m),
1020 (m), 944 (w), 810 (m), 763 (w), 740 (m), 690 (m), 649 (w). EI-
MS: m/z 338 [M - TolNCS - NPh2]
þ (20%). Anal. Found
(calcd for C38H49N5STi): C, 69.63 (69.60); H, 7.60 (7.53); N,
10.63 (10.68).
Cp*Ti{MeC(NiPr)2}{N(NPh2)C(N
tBu)O} (30).To a solution
of Cp*Ti{MeC(NiPr)2}(NNPh2) (13; 0.300 g, 0.590 mmol) in
benzene (20 mL) was added tBuNCO (67.6 μL, 0.590 mmol), all
at room temperature. An immediate color change from dark
yellow to dark brown was observed. After 16 h, the volatiles
were removed under reduced pressure to afford 30 as a dark
brown solid. The resultant dark brown solid was washed with
cold pentane (3  5 mL), filtered, and dried in vacuo. Yield:
0.184 g (51%). 1HNMR (C6D6, 299.9MHz, 293K): δ 7.62 (2H,
d, 3J = 6.5 Hz, oa-C6H5), 7.22 (2 H, t,
3J = 6.5 Hz, ma-C6H5),
7.09 (2H, d, 3J=6.5Hz, ob-C6H5), 7.01 (2H, t,
3J=6.5Hz,mb-
C6H5), 6.88 (1 H, t,
3J=6.5 Hz, pa-C6H5), 6.71 (1 H, t,
3J=6.5
Hz, pb-C6H5), 3.34 (1 H, app sept, app
3J = 6.5 Hz,
NCHaMeMe), 2.80 (1 H, app sept, app
3J = 6.5 Hz,
NCHbMeMe), 1.96 (15 H, s, C5Me5), 1.56 (9 H, s,
tBu), 1.39
(3 H, s, MeCN2), 1.17 (3 H, d,
3J = 6.5 Hz, NCHaMeMe), 1.14
(3 H, d, 3J = 6.5 Hz, NCHaMeMe), 1.09 (3 H, d,
3J = 6.5 Hz,
NCHbMeMe), 0.92 (3 H, d,
3J = 6.5 Hz, NCHbMeMe).
13C-
{1H} NMR (C6D6, 75.4 MHz, 293 K): δ 168.5 (MeCN2), 152.4
(OC(N)N), 148.1 (ia-C6H5), 147.8 (ib-C6H5), 128.4 (C5Me5),
128.3 (ma-C6H5), 128.1 (mb-C6H5), 121.7 (pa-C6H5), 121.6 (oa-
C6H5), 119.3 (pb-C6H5), 117.7 (ob-C6H5), 51.90 (NCMe3), 50.4
(NCHaMeMe), 49.5 (NCHbMeMe), 32.9 (NCMe3), 26.2
(NCHbMeMe), 25.1 (NCHbMeMe), 25.0 (NCHaMeMe),
24.35 (NCHaMeMe), 13.0 (MeCN2), 12.9 (C5Me5). IR (NaCl
plates, Nujol mull, cm-1): ν 1653 (m), 1636 (w), 1589 (w), 1559
(w), 1540 (w), 1521 (w), 1506 (w), 1490 (m), 1458 (s), 1335 (w),
1313 (w), 1207 (w), 1175 (w), 1019 (w), 793 (w), 744 (w), 691 (w),
668 (m). Anal. Found (calcd for C35H51N5OTi): C, 69.52
(69.41); H, 8.42 (8.49); N, 11.48 (11.56).
Cp*Ti{MeC(NiPr)2}{OC(NTol)N(NPh2)C(O)O} (31). A so-
lution of Cp*Ti{MeC(NiPr)2}{N(NPh2)C(NTol)O} (24; 0.450
g, 0.700 mmol) in toluene (20 mL) was freeze-pump-thawed
three times. The solution was then exposed to CO2 at a pressure
of ca. 1.1 atm at room temperature. After 4 days, the volatiles
were removed under reduced pressure to afford 31 as a dark
brown solid. The resultant dark brown solid was washed with
cold pentane (3  5 mL), filtered, and dried in vacuo. Yield:
0.178 g (37%). 1HNMR (C6D6, 299.9MHz, 293K): δ 7.95 (2H,
d, 3J = 6.0 Hz, oa-C6H5), 7.40 (2 H, d,
3J = 6.0 Hz, ob-C6H5),
7.29 (2H, t, 3J=6.0Hz,ma-C6H5), 7.10 (2H,m,mb-C6H5), 7.00
(4H,m, overlapping o- andm-C6H4Me), 6.98 (1H,m, pa-C6H5),
6.82 (1H, t, 3J=6.0Hz, pb-C6H5), 3.47 (1H, app sept, app
3J=
6.0 Hz, NCHaMeMe), 3.35 (1 H, app sept, app
3J = 6.0 Hz,
NCHbMeMe), 2.19 (3 H, s, C6H4Me), 1.83 (15 H, s, C5Me5),
1.44 (3 H, s, MeCN2), 1.13 (3 H, d,
3J = 6.0 Hz, NCHaMeMe),

1200 Organometallics, Vol. 30, No. 5, 2011 Tiong et al.
1.09 (3H,d, 3J=6.0Hz,NCHaMeMe), 0.88 (6H,overlappng2 d,
3J = 6.0 Hz, overlapping NCHbMeMe and NCHbMeMe).
13C{1H} NMR (C6D6, 75.4 MHz, 293 K): δ 169.6 (MeCN2),
152.8 (OC(O)N), 149.9 (OC(N)N), 147.1 (i-C6H4Me), 146.6 (ib-
C6H5), 146.2 (ia-C6H5), 130.9 (C5Me5), 130.4 (p-C6H4Me), 128.9
(ma-C6H5), 128.8 (overlappingm-C6H4Me andmb-C6H5), 123.9
(o-C6H4Me), 123.1 (pa-C6H5), 122.5 (oa-C6H5), 121.0 (pb-C6H5),
118.2 (ob-C6H5), 50.5 (NCHaMeMe), 50.0 (NCHbMeMe), 24.3
(NCHaMeMe), 23.9 (NCHbMeMe), 23.5 (overlapping NCHa-
MeMe and NCHbMeMe), 21.0 (C6H4Me), 14.9 (MeCN2), 12.6
(C5Me5). IR (NaCl plates, Nujol mull, cm
-1): ν 1699 (s), 1628
(s), 1592 (s), 1496 (s), 1336 (s), 1207 (m), 1180 (m), 1101 (m), 1017
(w), 862 (w), 794 (m), 746 (m), 690 (w). EI-MS: m/z 424 [M -
NPh2 - Tol]
þ (30%). Anal. Found (calcd for C39H49N5O3Ti):
C, 68.55 (68.51); H, 7.15 (7.22); N, 10.18 (10.24).
Reaction of Cp*Ti{MeC(NiPr)2}(NNMe2) (15) with Ar0NCO.
To a solution of Cp*Ti{MeC(NiPr)2}(NNMe2) (15; 0.417 g, 1.09
mmol) in benzene (20 mL) was added Ar0NCO (467 μL, 2.18
mmol), all at room temperature. The resulting yellow solution was
stirred for 20 h at 60
C. Volatiles were then removed under
reduced pressure to afford [Cp*Ti{MeC(NiPr)2}(μ-O)]2 (12) and
1,2,4-N(Me)2NC(NAr0)N(Ar0)C(O) (34). Sublimation (65-75

C, 5  10-6 mbar) afforded 34 as a white solid. Yield: 76 mg
(15%). Diffraction-quality crystals were grown from a concen-
trated hexane solution at-4
C. 1HNMR (C6D6, 499.9MHz, 293
K): δ 7.25 (1 H, t, 3J=7.5 Hz, pa-C6H3(
iPr2)), 7.14 (2 H, d,
3J=
7.5Hz,ma-C6H3(
iPr2)), 7.09 (2 H, d,
3J=7.5Hz,mb-C6H3(
iPr2)),
7.00 (1H, t, 3J=7.5Hz, pb-C6H3(
iPr2)), 3.43 (2H, app sept, app
3J
= 7.0 Hz, NCHbMeMe), 3.20 (2 H, app sept, app
3J = 7.0 Hz,
NCHaMeMe), 2.66 (6 H, s, NNMe2), 1.32 (6 H, d,
3J = 7.0 Hz,
NCHaMeMe), 1.21 (18 H, m, overlapping NCHaMeMe,
NCHbMeMe, and NCHbMeMe).
13C{1H} NMR (C6D6, 125.7
MHz, 293 K): δ 159.7 (NC(O)N), 152.9 (NC(N)N), 147.2 (oa-
C6H3(
iPr2)), 146.4 (ib-C6H3(
iPr2)), 140.4 (ob-C6H3(
iPr2)), 130.5 (pa-
C6H3(
iPr2)), 128.3 (ia-C6H3(
iPr2)), 124.1 (ma-C6H3(
iPr2)), 122.7
(mb-C6H3(
iPr2)), 122.2 (pb-C6H3(
iPr2)), 53.5 (NNMe2), 29.5
(CHaMeMe) 28.3 (CHbMeMe), 25.0 (CHaMeMe), 24.3
(overlapping CHbMeMe and CHbMeMe), 22.9 (CHaMeMe). IR
(NaCl plates, Nujol mull, cm-1): ν 2289 (w), 2169 (w), 1808 (s),
1646 (s), 1586 (m), 1465 (s), 1393 (s), 1365 (m), 1356 (w), 1290 (w),
1237 (m), 1207 (w), 1172 (w), 1114 (w), 1063 (m), 1041 (w), 965
(m), 936 (w), 908 (w), 862 (w), 810 (w), 801 (m), 777 (m), 754 (w),
725 (s), 706 (m), 690 (m), 640 (m). EI-MS: m/z 448 [M]þ (100%),
245 [M - ArNCO]þ (80%). Anal. Found (calcd for
C64H104N8O3Ti2): C, 67.99 (68.07); H, 9.20 (9.28); N, 10.02 (9.92).
Cp*Ti{MeC(NiPr)2}{OC(NNMe2)N(Tol)C(NTol)O} (35).
To a solution of Cp*Ti{MeC(NiPr)2}(NNMe2) (15; 0.300 g,
0.780 mmol) in benzene (20 mL) was added p-TolNCO (0.198
mL, 1.57 mmol), all at room temperature. An immediate color
change from dark green to brown was observed, and the
solution was left to stand for 16 h. Volatiles were then removed
under reduced pressure to afford 35 as a brown solid. The
resultant brown solid was washed with cold pentane (3  5
mL), filtered, and dried in vacuo. Yield: 0.308 g (76%). Diffrac-
tion-quality crystals were grown by slow cooling of a saturated
hexane solution. 1H NMR (C6D6, 299.9 MHz, 293 K): δ 7.51 (2
H, d, 3J = 8.4 Hz, ob-C6H4Me), 7.12 (2 H, d,
3J = 8.4 Hz, oa-
C6H4Me), 7.07 (2 H, d,
3J=8.4 Hz,mb-C6H4Me), 7.01 (2 H, d,
3J=8.4Hz,ma-C6H4Me), 3.71 (1H, app sept, app
3J=6.6Hz,
NCHaMeMe), 3.42 (1 H, app sept, app
3J = 6.6 Hz,
NCHbMeMe), 2.50 (6H, s, NNMe2), 2.20 (3 H, s, C6H4Mea),
2.05 (3 H, s, C6H4Meb), 2.02 (15 H, s, C5Me5), 1.50 (3 H, s,
MeCN2), 1.26 (3 H, d,
3J=6.6 Hz, NCHaMeMe), 1.15 (3 H, d,
3J = 6.6 Hz, NCHaMeMe), 0.94 (3 H, d,
3J = 6.6 Hz,
NCHbMeMe), 0.85 (3 H, d,
3J = 6.6 Hz, NCHbMeMe).
13C-
{1H} NMR (C6D6, 75.4 MHz, 293 K): δ 169.7 (MeCN2), 157.6
(OC(NNMe2)N), 153.2 (OC(NTol)N), 148.1 (ia-C6H4Me),
142.1 (ib-C6H4Me), 134.9 (pb-C6H4Me), 130.1 (ob-C6H4Me),
129.7 (C5Me5), 129.2 (ma-C6H4Me), 128.6 (overlapping pa-
and oa-C6H4Me), 124.3 (mb-C6H4Me), 50.1 (NCHaMeMe),
49.7 (NCHbMeMe), 48.5 (NNMe2), 24.1 (NCHaMeMe), 24.1
(NCHbMeMe), 23.8 (NCHaMeMe), 23.5 (NCHbMeMe), 21.1
(C6H4Meb), 21.0 (C6H4Mea), 15.5 (MeCN2), 12.5 (C5Me5). IR
(NaCl plates, Nujol mull, cm-1): ν 2805 (m), 2757 (w), 1619 (s),
1599 (s), 1568 (s), 1508 (s), 1458 (s), 1416 (w), 1366 (s), 1340 (m),
1311 (m), 1279 (w), 1255 (m), 1227 (m), 1204 (s), 1171 (w), 1158
(w), 1119 (m), 1105 (m), 1024 (w), 1005 (s), 933 (w), 899 (m), 884
(m), 810 (s), 780 (m), 725 (m), 718 (m), 688 (w), 605 (m). Anal.
Found (calcd for C36H52N6O2Ti): C, 66.73 (66.65); H, 7.98
(8.08); N, 12.95 (12.96).
Crystal Structure Determinations. Crystal data collection and
processing parameters for Cp*Ti{MeC(NiPr)2}(NNPh2) (13),
Cp*Ti{MeC(NiPr)2}(NNMePh) (14), Cp*Ti{MeC(N
iPr)2}-
(NNMe2) (15), Cp*Ti{MeC(N
iPr)2}{OC(O)N(NPh2)C(O)O}
(18), Cp*Ti{MeC(NiPr)2}{OC(O)-N(NMe2)C(O)O} (19), Cp*Ti
{MeC(NiPr)2}{OC(O)N-(NNMePh)C(O)O} (36), Cp*Ti{MeC-
(NiPr)2}{N(NPh2)C(NAr0)O} (27), Cp*Ti{MeC(N
iPr)2}{N-
(NPh2)C(NAr0)S} (29), 1,2,4-N(Me)2NC(NAr0)N(Ar0)C(O) (34),
and Cp*Ti{MeC(NiPr)2}{OC(NNMe2)N(Tol)C(NTol)O} (35)
are given in the Supporting Information. Crystals weremounted
on glass fibers using perfluoro polyether oil and cooled rapidly
in a stream of coldN2 using anOxfordCryosystemsCryostream
unit. Diffraction data were measured using an Enraf-Nonius
KappaCCD diffractometer. As appropriate, absorption and
decay corrections were applied to the data and equivalent
reflections merged.74 The structures were solved by direct
methods (SIR9275), and further refinements and all other crys-
tallographic calculationswere performed using theCRYSTALS
program suite.76 Other details of the structure solution and
refinements are given in the Supporting Information (CIFdata).
Full listings of atomic coordinates, bond lengths and angles, and
displacement parameters for all the structures have also been
deposited at the Cambridge Crystallographic Data Centre. See
the Notice to Authors at http://pubs.acs.org/paragonplus/sub-
mission/orgnd7/orgnd7_authguide.pdf.
Computational Details. All the calculations have been per-
formedwith theGaussian03 package77 at the B3PW91 level.78,79
The titanium atom was represented by the relativistic effec-
tive core potential (RECP) from the Stuttgart group (12
valence electrons) and its associated basis set,80 augmented by
an f polarization function (R = 0.869).81 The S atom was
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Barone, V.;Mennucci, B.; Cossi,M.; Scalmani, G.; Rega, N.; Petersson,
G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.;Klene,M.; Li,X.;Knox, J. E.;Hratchian,H. P.; Cross, J. B.; Bakken,
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Article Organometallics, Vol. 30, No. 5, 2011 1201
represented by RECP from the Stuttgart group and the
associated basis set,82 augmented by a d polarization function.83
The remaining atoms (C, H, N, O) were represented by
a 6-31G(d,p) basis set in all cases, except for the bond
energy calculations on Figure 14, where a 6-311þþG(d,p) basis
set was used.84 NBO analyses were performed with NBO
5.0 interfaced with Gaussian.85 Full optimization of geometry
was performed without any symmetry constraint, followed
by analytical computation of the Hessian matrix to identify
the nature of the located extrema as minima or transition
states. Connection between reactant and product through a
given transition state was checked by optimization of slightly
altered geometries of the transition state along the two direc-
tions of the transition state vector associated with the imaginary
frequency.
Acknowledgment. We thank the Malaysian Higher
EducationMinistry for a scholarship to P.J.T., the EPSRC
for a studentship to A. D. Schofield, a Ph.D plus post-
doctoral award to J.D.S., and a postdoctoral fellowship to
A. D. Schwarz. We also thank the Spanish MICINN for a
MEC postdoctoral fellowship to A.N. Dr. A. R. Cowley is
thanked for collecting the X-ray data for 13.
Supporting Information Available: Text, tables, figures, and
CIF files giving X-ray data collection and processing param-
eters, X-ray crystallographic data for the structure determina-
tions of Cp*Ti{MeC(NiPr)2}(NNPh2) (13), Cp*Ti{MeC-
(NiPr)2}(NNMePh) (14), Cp*Ti{MeC(N
iPr)2}(NNMe2) (15),
Cp*Ti{MeC(NiPr)2}{OC(O)N(NPh2)C(O)O} (18), Cp*Ti{Me-
C(NiPr)2}{OC(O)N(NMe2)C(O)O} (19), Cp*Ti{MeC(N
iPr)2}-
{OC(O)N(NNMePh)C(O)O} (36), Cp*Ti{MeC(NiPr)2}{N-
(NPh2)C(NAr0)O} (27), Cp*Ti{MeC(N
iPr)2}{N(NPh2)C(NA-
r0)S} (29), 1,2,4-N(Me)2NC(NAr0)N(Ar0)C(O) (34), and Cp*Ti-
{MeC(NiPr)2}{OC(NNMe2)N(Tol)C(NTol)O} (35), selected
distances and angles for 1,2,4-N(Me)2NC(NAr0)N(Ar0)C(O)
(34), further experimental details, a description of the reactions of
14withCO2andCS2,and furtherdetailsof thecalculations.Thisma-
terial is available freeof chargevia the Internet athttp://pubs.acs.org.
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A.; Jonas, V.; K€ohler, K. F.; Stagmann, R.; Veldkamp,A.; Frenking,G.
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