Difluorocarbene insertion into Si-H bonds: the preparation and properties of difluoromethylsilanes

Article abstract of DOI:10.1016/0022-328X(91)86223-D

Difluorocarbene, CF2, generated by thermal decomposition of CF3SiF3 at 100 deg C, has been found to insert into the Si-H bonds of halosilanes SiH3X (X = F, Cl, Br, I), methylhalosilanes CH3SiH2X (X = Br, Cl) and (CH3)2SiHCl, and disiloxane (SiH3)2O.Use of excess of the CF2-source CF3SiF3 and of pressure favour the formation of the di-insertion products (CHF2)2SiHX and (CHF2)2(CH3)SiX. (CHF2)3SiCl was identified among the products formed in the co-thermolysis of CF3SiF3 and (CHF2)SiH2Cl.In contrast, organosilanes R_nSiH_4-n (R = Me, Ph; n = 0-4), dihalosilanes SiH2X2 and RSiHX2, trihalosilanes HSiX3 and tetrahalosilanes SiX4 do not react with CF2 under these conditions.The reactivity and selectivity of difluorocarbene is discussed in terms of steric and electronic parameters.A kinetic deuterium effect, k(SiH)/k(SiD) 1.14, has been observed for the insertion into MeSiH2Cl.The mostly novel products were characterized by vibrational and multinuclear NMR spectroscopy.Difluoromethylsilane, (CHF2)SiH3, has been obtained from (CHF2)SiH2Cl and LiAlH4 in almost quantitative yield, and its vibrational spectrum has been recorded and interpreted with the assistance of a normal coordinate analysis.