Early metal-thiolate bond

Bond enthalpies reported by Dias and Martinho Simoes for a series of MCp2(XR)j complexes (where X = O and S) show that the M-S bonds are 24r-29 kcal/mol weaker than the corresponding M-0 bonds. For instance, the M-X bond enthalpy in Ti(Cp)2(SCgHj)2 is 86 kcal/mol, whereas the M-X bond enthalpy in the related alkoxo complex, Ti(Cp)2(OCgH5)2, is 110 kcal/mol. Thus, the early-metal-thiolate bond is weaker (or the early-metal-alkox-ide bond is stronger) than would be expected based on the H-X bond strengths. 

This greater strength of the late-metal-thiolate bond compared to the early-inetal-thi-olate bond or the late-metal-alkoxide bond has been rationalized in two ways. First, the late-metal-thiolate bond involves the favorable match of a soft ligand with a soft metal. Second, this bond involves a larger covalent component than the bond of a late metal to an alkoxide or an early metal to a thiolate. ... 

As the field of metal carbonyl cluster chemistry was expanding rapidly many other new classes of clusters joined the fold, in particular, gold phosphine clusters, metal-alkoxide, -thiolate, and -halide clusters of the early transition elements. The theories of bonding in metal clusters rapidly advanced aided by both computational procedures and conceptual ideas. Without a doubt the most significant in the latter... 

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