Synthesis of Metal-Silyl Complexes

200 CHAPTER 4 covalent (x-TYPE) LIGANDS BOUND THROUGH METAL-HETEROATOM BONDS 

Transition-metal-silyl complexes are also formed by the reactions of metal-alkyl complexes with silanes to form free alkane and a metal-silyl complex. Two examples are shown in Equations 4.114 and 4.115. ° The synthesis of silyl complexes by this method has been accomplished with both early and late transition metal complexes. The formation of metal-silyl complexes from late-metal-alkyl complexes resembles the hydrogenolysis of metal-alkyl complexes to form metal hydrides and an alkane. The mechanisms of these reactions are discussed in Chapter 6. In brief, these reactions with late transition metal complexes to form silyl complexes typically occur by a sequence of oxidative addition of the silane, followed by reductive elimination of alkane. An example of this is shown in the coupling of 1,2-bis-dimethylsilyl benzene with a dimethyl platinum(II) complex (Equation 4.114). Similar reactions occur with d° early metal complexes by a a-bond metathesis process that avoids these redox events. For example, the reaction of Cp ScPh with MesSiH, has been shown to proceed through this pathway (Equation 4.115).  

Finally, metal-silyl complexes are commonly prepared by insertion of a transition metal fragment into the Si-H or Si-X bond of a silane or halosilane. These oxidative addition processes are presented in detail in Chapter 6. This process forms the silyl complexes that are the intermediates in transformations of silanes catalyzed by late transition metal complexes. Two examples of this route to sUyl complexes, one by addition of an Si-H bond and one by addition of an Si-X bond, are shown in Equations 4.116 and 4.117. --  

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