SEARCH FOR RADICAL REARRANGEMENT IN ORGANOSILICON SYSTEMS .I. ALPHA-SILYL RADICALS FROM SILANEOPHYL SYSTEMS

The triphenylsilylmethyl radical (1), generated by the dw-butyl peroxide decarbonylation of neat β,β,β-triphenylsilylacetaldehyde (4), did not rearrange under the conditions employed. Only triphenylmethylsilane (10) resulted. Dilution of 4 in chlorobenzene did not alter the result. This same radical, as well as the phenyl-dimethylsilylmethyl (silaneophyl) and trimethylsilylmethyl (silaneopentyl) radicals 2 and 3, respectively, were generated from their corresponding chlorides by means of ethyl Grignard reagent and a small amount of cobaltous chloride (Kharasch-Grignard technique). The reactions proceeded vigorously and high mass balances were obtained in the phenyl cases. Detailed analysis of the products from 1 and 2 indicated that no rearrangement occurred. Both monomeric and dimeric products were unrearranged. From radical 1 resulted 10 (23%) and the dimer 1,1,1,4,4,4-hexaphenyl-1,4-disilabutane (12,72%). From radical 2 came trimethylphenylsilane (13,29%) and the dimer 2,5-dimethyl-2,-diphenyl-2,5-disilahexane (bisilaneophyl, 15, 64%). The products from 3 were also unrearranged, viz., tetramethylsilane (19, 17%) and the dimer 2,2,5,5-tetramethyl-2,5-disilahexane (20, 27%). However, in this case, the volatility of the products reduced the mass balance achieved. Small amounts of ethylated products were also produced in these reactions, coming from ethyl radical capture of the unrearranged α-silyl radicals. A particularly careful search for rearrangement was done in the silaneophyl case. Rearranged monomeric and dimeric products were alternatively synthesized and shown to be absent in the Kharasch-Grignard reaction. The following antirearrangement factors possible in α-silyl radicals are mentioned and discussed: energetics, steric effects, concertedness (push-pull effects), and dγ-pγ electron derealization (back-bonding). © 1969, American Chemical Society. All rights reserved.