Relatively stable silaethylenes. Photolysis of acylpolysilanes

Acyl Silanes

“…The very low yield of benzoyl triphenylsilane (6%) obtained, and the similar yields of acetyl triphenylsilane obtained from the reactions of silyl lithium reagents with acetyl chloride 71 , demonstrate that this is not a useful method for the synthesis of simple acyl silanes. It is, however, successful for the preparation of acyl tris(trimethylsilyl)silanes and some derivatives 24,31,72,73 . Tris(trimethylsilyl) and alkyl bis(trimethylsilyl)silyl lithium reagents react cleanly with acyl chlorides, typically at 0°C, to give the corresponding acyl silanes in up to ca 85% yields.…”

“…The acyl silane unit is thus acting as a formal geminal diradical species. An interesting development of this reaction includes a stannyl group at the halo-(or xanthate-) bearing carbon atom, cyclization of an˛-stannyl radical then resulting in formation of an˛-stannylated silyloxy radical, from which the stannyl unit is lost, providing a regiospecific synthesis of cyclic silyl enol ethers (Scheme 86) 200 Cycloaddition reactions of acyl silanes appear to be rare, but Brook has shown that˛-silyloxy bis(trimethylsilyl)silenes (52), generated photochemically from acyl tris(trimethylsilyl)silanes (vide infra, Section IV.A.4), undergo [2 C 2] and [4 C 2] cycloaddition reactions with ketones, and [4 C 2] cycloaddition reactions with less bulky acyl silanes, as illustrated in Scheme 87 17,24,26,72,73,201 …”

The positions of λmax for some trimethylsilyl-substituted silylenes

“…Although the primary photochemical events of polysilane photolysis have typically provided silylenes, a variety of other pathways have been observed. For example, photolysis of molecules containing the tris(trimethylsilyl)silyl group in conjunction with unsaturated chromophores such as a vinyl [6], acyl [7], and phosphirenyl [8] functionalities yields silenes and rearrangement products [9]. Spectral observation of the n ~ p transition for a wide variety of silylenes frozen in low-temperature organic glasses, supported by chemical trapping studies, has allowed identification of divalent silicon intermediates from the photolysis of polysilanes [10].…”

Head-to-Head versus Head-to-Tail Dimerizations of Transient Silenes – The Solvent-Dependent Regiospecifity of the Dimerization of 2-(2-Methoxyphenyl)-1,1-bis(trimethylsilyl)silene

“…Transient 1,1-bis(trimethylsilyl)silenes, made by the photolysis of acyl-tris(trimethylsilyl)silanes [2] or by a modified Peterson reaction [2] [3] [4] , generally dimerize in a head-to-head mode. The reaction is supposed to proceed through radical intermediates [5] . After SiϪSi bond formation the resulting diradicals stabilize with the formation of products, the structures of which depend on the nature of the substituents at the silene carbon atom (Eq.…”

“…When at least one of the silene C substituents is an aryl group, moderately stable tetrahydro-2,3-disilanaphthalenes 2 [6] are in some cases isolated as the kinetically preferred formal [2 ϩ 4] silene dimers, which on thermal treatment gradually isomerize to give 1. Silenes containing α hydrogen in the substituent at the silene C atom ("allylic" hydrogen) stabilize preferentially under hy-stituent, causing an intermolecular interaction with the electrophilic silene silicon atom of a neighboring silaethene drogen transfer to give linear dimers 3 [2] [3a] [5] [7] . Recently we found that 2-(2-dimethylaminophenyl)-1,1-molecule.…”