Manganese silyl complexes reductive elimination

Although even in the IiAUi cleavage of the Si-Pt bonds a reductive elimination process is likely to occur, since the configuration at silicon is almost completely retained, a nucleophilic displacement of the silyl ligand is still conceivable. Deuterium labeling experiments have unambiguously demonstrated this possibility in silyl-manganese complexes (213). 

The easy reductive elimination process does not seem to arise from a particular lability of hydrosilane adduct 166. Complex 166 is stable in solution. Moreover, functionalized silyl-manganese complexes were shown to undergo substitution at silicon without Si-Mn bond cleavage (251) (Scheme 58). 

To explain their results, Hart-Davies and Graham proposed to depict manganese complexes 172 in terms of resonance hybrids between representations 178 and 179 (261) (Figure 18). However, the possibility that the close Si-H distance is due to steric constraints has been raised by Bennett and Simpson (264). Steric effects favor a cis orientation of silyl and hydrido ligands and thus facilitate reactions involving reductive elimination pathways. 

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