Solvent, Substituent, and Temperature Effects on the Absolute Rate Constants for Addition of Methoxytrimethylsilane to 1,1-Diarylsilenes

Abstract

Absolute rate constants have been measured for the reaction of methoxytrimethylsilane with a series of transient, para-substituted 1,1-diphenylsilenes (H2CSi(C6H4X)2, where X = H, Me, F, Cl, and CF3) in hexane solution at room temperature. The data correlate with Hammett substituent constants, affording the reaction constant ρ = +0.9 ± 0.2. For the parent compound and the 4,4‘-bis(trifluoromethyl) derivative, rate constants have been determined over the 0−60 °C temperature range in hexane, 1,2-dichloroethane, and acetonitrile solution. The rate constants for reaction of the parent compound increase in the order hexane ≈ 1,2-dichloroethane < MeCN, but are relatively insensitive to solvent in the other case. However, differences are revealed in the Arrhenius activation energies for reaction, which are negative for both compounds in all three solvents. Those for the 4,4‘-bis(trifluoromethyl) compound in particular change to more positive values with increasing solvent polarity. The data are consistent with a...