Time resolved kinetic studies of the gas‐phase reactions of dimethylsilylene with some O‐Donor molecules: Part I. Room temperature studies

The reactions of dimethylsilylene, SiMe 2 , generated by laser flash photolysis from pentamethyldisilane and octamethyltrisilane, and detected via its 457.9 nm absorption, have been investigated with a number of oxygen containing molecules, including oxygen itself, carbon monoxide, water, alcohols, and ethers at 295 K. Some substrate molecules were deuterated. Apart from CO, all molecules reacted with SiMe 2 with second order rate constants (in cm 3 molecule −1 s −1 ) in the range 7.7 ± 10 −14 to 4.7 ± 10 −11 . While most of the reactions of SiMe 2 studied went to completion those with dimethylether and tetrahydrofuran were partially reversible. The reaction of SiMe 2 with oxirane was pressure dependent. The data are generally consistent with a mechanism involving initial formation of a donoracceptor, zwitterionic complex. In the case of reaction with alcohols, there is a small overall isotope effect, suggesting formation of a complex followed by rapid H‐transfer, which only marginally affects the rate. In the case of ethers, complexes are formed which (i) may react further (Me 2 Si…oxetane), (ii) may react further but also reversibly decompose (Me 2 Si…oxirane), or (iii) do not seem to react further (Me 2 Si…OMe 2 , Me 2 Si…THF) but partially redissociate. The donor‐acceptor bond strength has been estimated in these last cases to be ca. 40 kJ mol −1 . Supporting arguments and mechanistic details of all reactions investigated are presented.