Laser Pulse Photolysis of 7-Silanorbornadiene in Solution: Experimental and AM1 Studies of Complexation between Silylenes and CHBr3

Article abstract of DOI:10.1021/j100040a020

The quantum yield (0.95 +/- 0.1) for the decomposition of 7,7-dimethyl-1,4,5,6-tetraphenyl-2,3-benzo-7-silanorbornadiene (Ib) in hexane at room temperature has been determined by the laser pulse photolysis technique.Reaction rate constants of the generated dimethylsilylene with bromoform (4.4 * 10⁷ M^-1 s^-1) and Ib (5.7 * 10⁹ M^-1 s^-1) have been measured.It is suggested that the reaction of Me2Si: with CHBr3 occurs via the formation of an intermediate complex (λ_max = 338 nm, ε =1280 M^-1 cm^-1).The bimolecular rate constant for decay of the complex (2k = 1.61 * 10⁹ M^-1 s^-1) has also been estimated.Semi-empirical PM3 calculations of the model reaction between the singlet SiH2 and CHBr3 show the formation at the first step of the reaction of a donor-acceptor complex stabilized by interactions between a vacant p-AO of SiH2 and a lone pair of one of the Br atoms.Such a complex should be rather stable both toward dissociation into the starting reagents (E = 23.3 kcal/mol) and further rearrangement into the insertion product, Br(H2)SiCHBr2 (E = 22.3 kcal/mol).