Nucleophilic displacements of silyl ligands

C. Chiral Silyl-Transition Metal Complexes Nucleophilic Displacement of Silyl Ligands... 

The mechanism and stereochemistry of nucleophilic substitution at silicon, including displacement of silyl ligands in silicon-transition metal complexes. 

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). 

An electron-transfer in the first step would give cationic intermediate 168. Formation of R3 SiX may then arise via a direct nucleophilic displacement of the silyl ligand, or through the neutral intermediate 169 by a reductive-elimination process. Cleavage reaction may also occur by competitive pathways. In the present state of knowledge, since few experiments have been done, it is difficult to pinpoint definitive mechanisms. 

The tetracoordinate silicon cation is a rather common species in solution. It may be generated by heterolytic cleavage of a bond from silicon to a reactive ligand, as a result of interaction of the silicon center with an uncharged nucleophile like amine, imine, phosphine, phosphine oxide, and amide. Since these nucleophiles are also known to be effective catalysts for many displacements at silicon including important silylation processes (86,89,235-238), the cations of tetracoordinate silicon have received attention as possible intermediates in these reactions according to Eq. (40) (78,235,239-243). 

Halide ligands in early transition-metal silyl complexes are readily displaced with nucleophilic reagents (equation 39) to introduce a variety of functionalities cis to the silyl... 

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