Reactions of Cyclopentadienyl-Amidinate Titanium Imido
Compounds with CS2, COS, Isocyanates, and Other Unsaturated
Organic Compounds
Aldo E. Guiducci, Catherine L. Boyd, and Philip Mountford*
Chemistry Research Laboratory, UniVersity of Oxford, Mansfield Road, Oxford OX1 3TA, U.K.
ReceiVed September 10, 2005
New single-, double-, and cross-coupling and imido group transfer reactions of cyclopentadienyl-
amidinate titanium imido complexes are described. Reaction of Ti(Ł-C5R4Me)(NtBu)Cl(py) (R ) Me or
H) with the lithiated benzamidinate Li[PhC(NSiMe3)2] or acetamidinate Li[MeC(NiPr)2] afforded the
tert-butyl imido complexes Ti(Ł-C5R4Me)(NtBu){PhC(NSiMe3)2} (R ) Me (5) or H (7)) and Ti(Ł-C5R4-
Me)(NtBu){MeC(NiPr2)2} (R ) Me (6) or H (8)), respectively. Reaction of 6 with ArNH2 or TolNH2 (Ar
) 2,6-C6H3Me2, Tol ) 4-C6H4Me) afforded the corresponding aryl imido complexes Ti(Ł-C5-
Me5)(NR){MeC(NiPr2)2} (R ) Ar (9) or Tol (10)). Complexes 5, 7, and 8 underwent cycloaddition/
extrusion reactions with CS2 and COS to form í-sulfido dimers and tBuNCS and tBuNCO, respectively.
Compound 6 reacted with COS to form tBuNCO and [Ti(Ł-C5Me5)(í-S){MeC(NiPr)2}]2, but with CS2
additional insertion into an amidinate ligand Ti-NiPr bond occurred to form [Ti(Ł-C5Me5)(í-S){N-
(iPr)C(Me)N(iPr)C(S)S}]2. For the aryl imido compounds 9 and 10 the intermediate cycloaddition products
Ti(Ł-C5Me5){N(R)C(E)S}{MeC(NiPr)2} (E ) S or O) were observed. No further insertion of CS2 or
COS into the Ti-NR bonds occurred. All tert-butyl imido compounds reacted slowly with tBuNCO or
ArNCO to form í-oxo-bridged dimers and tBuNCNtBu or tBuNCNAr, respectively. Reaction of 9 with
tBuNCO gave the N,O-bound ureate Ti(Ł-C5Me5){N(Ar)C(NtBu)O}{MeC(NiPr)2}, which extruded
tBuNCNAr to form [Ti(Ł-C5Me5)(í-O){MeC(NiPr)2}]2. Reaction of 9 or 10 with aryl isocyanates gave
the N,O-bound ureates Ti(Ł-C5Me5){N(R1)C(NR2)O}{MeC(NiPr)2} (R1 ) Ar, R2 ) Ar or Tol; R1 )
Tol, R2 ) Ar or Tol (25)), which did not undergo extrusion. Reaction of 25 with TolNCO gave the net
cycloaddition-insertion product Ti(Ł-C5Me5){OC(NTol)NTolC(NTol)O}{MeC(NiPr)2}. Several hetero-
cumulene cross-coupling cycloaddition-insertion reactions were studied: for example, the sequential
reaction of 10 with TolNCO and CO2 gave Ti(Ł-C5Me5){OC(O)NTolC(NTol)O}{MeC(NiPr)2}. Aryl
imides 9 and 10 reacted with TolNCNTol to form the guanidinate complexes Ti(Ł-C5Me5){N(Tol)C-
(NTol)N(R)}{MeC(NiPr)2} (R ) Ar or Tol). Reaction of 5 and 6 with PhNO gave tBuNdNPh and
í-oxo-bridged dimers; the aryl imides 9 and 10 reacted similarly. Ketone and aldehyde CdO/TidNR
bond metathesis reactions occurred for certain tert-butyl and aryl imido compounds with MeCOMe,
PhCOPh, PhCOH, and PhCOMe, and in some instances intermediates were observed. Slow imide/imine
metathesis occurred between Ti(Ł-C5Me5)(N-4-C6H4NMe2){PhC(NiPr2)2} and PhCH(NTol). Compound
6 rapidly converted PhCONH2 and Me(CH2)4CONH2 to the corresponding nitriles, but the analogous
reaction with tBuCONH2 was slower. Several other titanium imido compounds and Ti(NMe2)2Cl2 were
also evaluated for the PhCONH2 dehydration reaction.
Introduction
Terminal transition metal imido compounds have been of
continuing interest for over two decades, and a good deal of
this chemistry has been reviewed.1-20 In terms of reaction
chemistry, the imido ligand (NR, where R is typically an organic
group) can act as either a spectator ligand (as found in imido-
supported olefin metathesis7,10,16 or Ziegler-Natta polymeri-
zation19 catalysts) or as a reactive site (typically via coupling
of the MdNR bond with unsaturated substrates, but also via
C-H bond activation). Some of the most reactive metal-imido
* To whom correspondence should be addressed. E-mail:
philip.mountford@chem.ox.ac.uk.
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1167Organometallics 2006, 25, 1167-1187
10.1021/om050784v CCC: $33.50 © 2006 American Chemical Society
Publication on Web 01/24/2006

linkages have been found for the group 4 elements.3,4,11,12,15,20,21
In this contribution we focus on titanium imido chemistry in
particular.22
As part of our program in this area,4,11,20 we reported
preliminary results for the reaction of the new cyclopentadienyl-
amidinate systems Ti(Ł-C5Me5)(NR){MeC(NiPr)2}23 (R ) tBu
or Ar (2,6-C6H3Me2)) with CO2.23 Cycloaddition reactions of
titanium imides with CO2 have been reported for a number of
other systems,24-27 but the cyclopentadienyl-amidinate systems
were especially interesting because the reaction products
ultimately formed showed a marked dependency on the imido
NR group. In the case when R ) tBu, CO2 cycloaddition (to
form N,O-bound carbamate complex 1a, Chart 1) was followed
by cycloreversion (extrusion of tBuNCO) to yield the í-oxo-
bridged dimer 2, whereas the corresponding reaction for 1b
(R ) Ar) yielded exclusively the double CO2 activation product
3 where a second CO2 molecule has inserted into the carbamate
Ti-N bond of 1b. Motivated by the potential of cyclopenta-
dienyl-amidinate titanium imido complexes to offer additional
variation or control of CO2 reactivity, we recently reported
comprehensive experimental and DFT computational studies of
the reactions of various pendant arm functionalized complexes
(for example 4, Chart 1) with CO2.28 The nature of the pendant
arm affected both the CO2 and isocyanate extrusion reaction
steps.
In this paper we report the synthesis and characterization of
new cyclopentadienyl-amidinate titanium imido complexes,
together with a detailed study of their reactions with other
organic substrates, namely, CS2, COS, isocyanates, carbodi-
imides, PhNO, ketones, PhCOH, PhC(NTol)H, and primary
organic amides. A part of the work was communicated previ-
ously.23
Results and Discussion
Synthesis of Cyclopentadienyl-Amidinate Imido Com-
pounds. The half-sandwich tert-butyl imido compounds Ti(Ł-
C5R5)(NtBu){PhC(NSiMe3)2} (R ) H or Me (5))29,30 have
previously been prepared from the imido-benzamidinate com-
plex Ti(NtBu){PhC(NSiMe3)2}Cl(py)2.31 To develop the chem-
istry of cyclopentadienyl-amidinate imido compounds further,
it was necessary to be able to vary the imido and amidinate
ligand N-substituents, as well as the cyclopentadienyl ligand
substituents. However, our attempts to develop a wider range
of amidinate-imido starting complexes Ti(NR){R2C(NR1)2}-
Cl(py)2 (R2, R1 other than phenyl, SiMe3; R ) tBu or aryl) met
with frustration, the products being ill-defined and rather
capricious in their handling. This is consistent with our previous
report that although reaction of Li[PhC(NSiMe3)2] with Ti(Nt-
Bu)Cl2(py)3 afforded the monomeric benzamidinate compound
Ti(NtBu){PhC(NSiMe3)2}Cl(py)2,31 the corresponding reaction
with Li[MeC(NCy)2] (Cy ) cyclohexyl) gave a poorly soluble,
dimeric product,30 thus showing the sensitivity of the reaction
and products to the particular amidinate ligand employed.
Our presently favored route to cyclopentadienyl-amidinate
imido compounds is summarized in Scheme 1 and starts from
the previously reported32 half-sandwich compounds Ti(Ł-C5R4-
Me)(NtBu)Cl(py) (R ) Me or H). As proof of method, we found
that reaction of Ti(Ł-C5Me5)(NtBu)Cl(py) with Li[PhC(N-
SiMe3)2] gave Ti(Ł-C5Me5)(NtBu){PhC(NSiMe3)2} (5) in 41%
(21) Odom, A. L. Dalton Trans. 2005, 225-233.
(22) For a very recent review and compilation of leading references in
titanium imido chemistry (covering aspects of molecular and supramolecular
structures and bonding; applications in olefin polymerization; uses in
materials chemistry; transformations involving the TidNR bond itself) see
ref 20.
(23) Guiducci, A. E.; Cowley, A. R.; Skinner, M. E. G.; Mountford, P.
J. Chem. Soc., Dalton Trans. 2001, 1392.
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Swallow, D.; Watkin, D. J. J. Chem. Soc., Dalton Trans. 1999, 379.
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Radius, U. Chem. Eur. J. 2003, 9, 3634.
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H.; Peng, S.-M.; Huang, J.-H. Inorg. Chem. 2004, 43, 6786.
(27) Boyd, C. L.; Toupance, T.; Tyrrell, B. R.; Ward, B. D.; Wilson, C.
R.; Cowley, A. R.; Mountford, P. Organometallics 2005, 24, 309.
(28) Boyd, C. L.; Clot, E.; Guiducci, A. E.; Mountford, P. Organo-
metallics 2005, 24, 2347.
(29) Stewart, P. J.; Blake, A. J.; Mountford, P. Organometallics 1998,
17, 3271.
(30) Stewart, P. J.; Blake, A. J.; Mountford, P. J. Organomet. Chem.
1998, 564, 209.
(31) Stewart, P. J.; Blake, A. J.; Mountford, P. Inorg. Chem. 1997, 36,
3616.
(32) Dunn, S. C.; Mountford, P.; Robson, D. A. J. Chem. Soc., Dalton
Trans. 1997, 293.
Chart 1 Scheme 1. Synthesis of Cyclopentadienyl-Amidinate Imido
Compounds
1168 Organometallics, Vol. 25, No. 5, 2006 Guiducci et al.