Oxidation of methylsilenes with molecular oxygen. A matrix isolation study

Article abstract of DOI:10.1021/ja00078a016

The photochemical and thermal oxidation of 1-methylsilene (2-silapropene) (1a), 1,1-dimethylsilene (1b), and 1,1,2-trimethylsilene (1c) has been investigated in O₂-doped argon matrices. All silenes 1 are easily photooxidized in matrices containing more than 1% O₂, but trimethylsilene (1c) is the only silene that exhibits thermal reactivity toward oxygen at temperatures as low as 20-40 K. The photochemical reactivity increases from 1a to 1c with increasing number of methyl groups at the double bond and decreasing ionization potential. Key intermediates in both the photochemical and the thermal oxidation of 1 are siladioxetanes 9. These species are labile even in low-temperature matrices and could not be identified spectroscopically, but evidence comes from the observed oxidation products such as a complex between methylsilanone and formaldehyde 8a and the formylsilanols 10. An additional oxidation pathway is observed for 1c with a methyl group at the C-atom of the silene moiety. Here, the primary adduct of 1c and ³O₂, triplet-diradical T-21c, can either ring-close to give dioxetane 9c and the products derived of it or produce dimethylvinylsilyl hydroperoxide (22) via H-abstraction from a methyl group.