Dehydrogenative coupling of silanes

The dehydrogenative coupling of silanes is a reaction type for the formation of Si-Si bonds. Although never commercialized, the reaction has been demonstrated for the synthesis of certain disilanes as well as polysilanes. These reactions generally require catalysts. The dehydrogenative coupling of silanes is a reaction type for the formation of Si-Si bonds. Although never commercialized, the reaction has been demonstrated for the synthesis of certain disilanes as well as polysilanes. These reactions generally require catalysts. Titanocene and related their complexes are typical catalysts. A typical reaction involves phenylsilane: Para- and meta-substituted phenylsilanes polymerize readily but ortho-substituted polymers were failed to form. Polymers white/colorless, tacky and soluble in organic solvents. Crosslinking was not observed. Using Cp2Ti(OPh)2 as a catalyst, the dehydrogenative coupling of phenylsilane in the presence of vinyltriethoxysilane produces a polysilane terminated with a triethoxysilylvinyl group. The nickel(I) complex 2 promotes the dehydrogenative coupling of some silanes. While catalysts for dehydrogenative coupling reactions generally tend to be transition metal complexes, magnesium oxide and calcium oxide for the conversion of phenylsilane. Being a heterogeneous process, the products are easily separated from the catalyst. Dehydrogenative coupling of primary silane using Wilkinson's catalyst is slow and dependent on the removal of H2 product. This conversion proceeds by oxidative addition of the Si-H bond and elimination of dihydrogen. Tris(pentafluorophenyl)borane (B(C6F5)3)) is another catalyst for the dehydrogenative coupling of tertiary silanes. This system has the useful characteristic of being selective for Si-H bonds vs Si-Si bonds, leading to fewer branches and more linear polymers. This catalyst is particularly useful in reactions involving thiols and tertiary silanes or disilanes. Due to steric factors, dehydrogenative coupling of tertiary silanes is slow. Disilane formation has been demonstrated in the presence of CpFe(CO)2CH3 combined with UV-irradiation. The mechanism is proposed to involve dissociation of CO ligand, oxidative addition of the Si-H center, followed by reductive elimination of methane. From there, the disilane R3Si-SiR3 is reductively eliminated from the complex.