Electrophilic cleavage reations of carbonsilicon bonds in neutral hexacoordinate silicon compounds: diorgano(phthalocyaninato)silicon

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Preparations of diorgano(phthalocyaninato)silicon [(Pc)Si(R 1)(R 2)] and their reactions with N-bromosuccinimide (NBS), halogens, copper(II) halides, and 3-chloroperbenzoic acid (MCPBA) are reported. The alkylsilicon bonds are readily cleaved by NBS, halogens, and CuX 2 to give the corresponding alkyl halides. The reactivity of arylsilicon bonds toward NBS and halogen depends greatly on the electronic effect of the substituent on the benzene ring, but these bonds are almost inert to CuX 2. The reactivity of the carbonsilicon bond towards NBS cleavage decreases in the order 4-MeOC 6H 4 > n-C 8H 17 > 4-MeC 6H 4 > Ph ⪢ 3-CF 3C 6H 4. Cleavage of alkylsilicon bonds may involve one-electron transfer from substrate to reagent and alkyl radical intermediates, while the electrophilic aromatic substitution mechanism may operate in the cleavage of arylsilicon bonds. [(Pc)SiR 2] are stable to MCPBA.