jo051145x_si_001.pdf (146.93 kB)
Download file

Sulfur Radical Cations. Kinetic and Product Study of the Photoinduced Fragmentation Reactions of (Phenylsulfanylalkyl)trimethylsilanes and Phenylsulfanylacetic Acid Radical Cations

Download (146.93 kB)
journal contribution
posted on 03.02.2006, 00:00 authored by Enrico Baciocchi, Tiziana Del Giacco, Fausto Elisei, Andrea Lapi
Laser and steady-state photolysis, sensitized by NMQ+, of PhSCH(R)X 14 (R = H, Ph; X SiMe3, CO2H) was carried out in CH3CN. The formation of 1+•4+• was clearly shown. All radical cations undergo a fast first-order fragmentation reaction involving C−Si bond cleavage with 1+• and 2+• and C−C bond cleavage with 3+• and 4+•. The desilylation reaction of 1+• and 2+• was nucleophilically assisted, and the decarboxylation rates of 3+• and 4+• increased in the presence of H2O. A deuterium kinetic isotope effect of 2.0 was observed when H2O was replaced by D2O. Pyridines too were found to accelerate the decarboxylation rate of 3+• and 4+•. The rate increase, however, was not a linear function of the base concentration, but a plateau was reached. A fast and reversible formation of a H-bonded complex between the radical cation and the base is suggested, which undergoes C−C bond cleavage. It is probable that the H-bond complex undergoes first a rate determining proton-coupled electron transfer forming a carboxyl radical that then loses CO2. The steady-state photolysis study showed that PhSCH3 was the exclusive product formed from 1 and 3 whereas [PhS(Ph)CH−]2 was the only product with 3 and 4.