Reactions of Nucleophiles and Electrophiles with Complexes

Abstract

Leonard et al. transformation of VCoSb and VFeSb involves an increase of coordination number. Interatomic distances between the constituent atoms of both MgCuSb-and Ni2In-type structures are shown in Table V. From these, it is seen that the nearest-neighbor distance between the transition metal and Sb shrinks from D(Co-Sb) = 0.2511 nm to D(Md-Sb) = 0.2425 nm, while that between the transition metals expands from Z)(V-Co) = 0.2511 nm to Z)(Ma-Ma) = 0.2699 nm in the transformation. In discussing interatomic distances in metal and inter-metallic compounds, Pearson pointed out that Pauling's bond-order rule appears to be most reliable6 D(n)-Z)(l) = 0.060 log n (Pauling's rule) In this equation n is the number of valence electrons per ligand, D(1) represents the single-bond distance calculated by using Pauling's single-bond radii7, and D(n) is the observed bond distance. In VCoSb-1 with the MgCuSb-type structure (Clb), Z)(Co-Sb) = 0.2511 nm is comparable with the sums of Co and Sb single-bond radii (Z)(l) = 0.2533 nm), while D(Co-V) = 0.2511 nm is larger than the sums of Co and V single-bond radii (0(1) = 0.2386 nm). The bond orders are calculated to be 1.17 for the Co-Sb bond and 0.62 for the Co-V bond. These values of bond order indicate that the Co-Sb bond is much stronger than the Co-V bond. Consequently, the Co atom is coordinated substantially by the four Sb atoms forming a tetrahedron due to the strong Co-Sb bond, although it is surrounded apparently by four Sb and four V atoms. That the bond order is 1.17 for the Co-Sb bond and that there is a tetrahedral bond directionality indicate that covalency between Co and Sb atoms occurs. In VCoSb-with the Ni2In-type structure (B82), Z)(Md-Sb) = 0.2425 nm is much smaller than the sums of Md and Sb single-bond radii (Z>(1) = 0.2584 nm), but D(Ma-Ma) = 0.2425 nm is larger than the single-bond separation between Ma atoms (Z>(1) = 0.2386 nm). The bond orders are calculated to be 1.84 for the Md-Sb bond and 0.30 for the MaMa bond. Considering the calculated value of n and the triangular bond directionality for the Md-Sb bond, a strong covalency between Md and Sb atoms is expected. It is concluded that the metal atom forms the covalent bond with the Sb atom in both MgCuSb-and Ni2In-type structures and that the strength of the covalent bond increases in the transformation from the MgCuSb-to Ni2In-type structure. New synthetic methods for the preparation of the disulfur complexes of molybdenum MoOS2(S2CNR2)2 (where R = CH3, C2H5, and m-C3H7) are described. The reactions of these disulfur complexes with a series of nucleophiles, N (N = P(OC2H5)3, P(C6H5)3, CH3NC, CN~, and S032"), have been characterized, and in each case the sulfur-substituted nucleophile (S~N) and MoO(S2CNR2)2 are produced. Reaction of MoOS2(S2CNR2)2 with C6H5SH or C6H5S" yields the dimeric molybdenum(V) complex Mo202S2(S2CNR2)2. The molybdenum-disulfur complexes do not react with the electrophile CH3I, but reaction with CH3S03F produces a new complex containing a persulfide ligand, [MoO(SSCH3)(S2CNR2)2]+. Characteristics of the synthetic molybdenum complexes are compared to those of certain molybdoenzymes which have been found to contain labile sulfur atoms. Reactions of the coordinated disulfur ligand in IrS2(dppe)2CI (where dppe = bis(diphenylphosphino)ethane) have also been studied. In contrast to the molybdenum systems, no reactions occur with the common thiophiles P(C6H5)3, P(OC2H5)3, and CN~. Methyl fluorosulfonate reacts to form a persulfide complex of Ir(III), [Ir(SSCH3)(dppe)2],2+ which has been characterized by 'H and 31P NMR, conductivity studies, and analytical data.