Titanocene and related their complexes are typical catalysts. A typical reaction involves phenylsilane:^[1][2]

n PhSiH₃ → [PhSiH]_n + n H₂

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.^[3]

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.^[4]

Other catalysts edit

The nickel(I) complex [(dippe)Ni(µ-H)]₂ promotes the dehydrogenative coupling of some silanes.^[5] While catalysts for dehydrogenative coupling reactions generally tend to be transition metal complexes, magnesium oxide and calcium oxide promote the dehydrogenation of phenylsilane. Being a heterogeneous process, the products are easily separated from the catalyst.^[6] Dehydrogenative coupling of primary silanes 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.^[7] Tris(pentafluorophenyl)borane (B(C₆F₅)₃)) is yet 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.^[8]

As well as being coupled to each other, tertiary silanes can be coupled with carboxylic acids to form silyl esters. Ru₃(CO)₁₂/EtI is a good catalyst for this. This reaction applies to a wide range of silanes and acids.^[9] The complex [Cu(PPh₃)₃Cl] can also be used to produce silyl esters.^[10]

Tertiary silanes may also be dehydrogenatively coupled to aromatic rings with the use of the catalyst Tp^Me2Pt(Me)₂H (Tp^Me2 = hydrido tris(3,5-dimethylpyrazolyl)borate). For example, this platinum catalyst can be used to react triethyl silane with benzene to produce phenyltriethylsilane, with the elimination of hydrogen gas. This is a terrific catalyst because it eliminates the need for a hydrogen acceptor, something which is normally required for the silation of a C-H bond. This reaction may also be done intramolecularly to produce five- or six-membered silicon-containing rings fused to a phenyl ring. In addition, tributylsilane can be converted into the corresponding cyclic organosilane via the same process. A drawback to this catalyst, however, is that it requires rather harsh reaction conditions (typically 200 °C for 24 hours for the intermolecular reaction, 48 – 72 hours for the intramolecular ones). It is also not particularly regioselective, so starting materials containing substituted benzene would result in a mixture of products.^[11]

Polymerization of silane edit

Some methods used to produce polysilanes are polymerization of masked dislenes,^[12] electroreduction of dichlorosilanes,^[13]

¹H and ²⁹Si NMR spectroscopy can sometimes be used to help identify and characterize products from these reactions.^[1]

Infrared spectroscopy may also be useful as it can indicate whether or not the product is a tertiary silane. The stretch for Si-H is seen at around 2100 and 910 cm⁻¹. In the case of tertiary silanes however, the peak at 910 cm⁻¹ is not seen. The shift or change in these peaks will be affected by the size of the polymer.^[1]