The insertion of silylene in C-H bonds; rate constant limits and the energy barrier

The technique of laser flash photolysis has been used to set limits on the rate constants for the bimolecular reactions of SiH2 with methane (CH4) and tetramethylsilane (SiMe4) at both ambient and elevated temperatures (ca 60 0 K). These limits show that the energy barriers to insertion reactions of SIH, in the C-H bends of CH,are at least 45(+/-6) kJ mol(-1) and in the C-H and/or Si-C bonds of SiMe4 are at least 23(+/-6) kJ mol(-1). The best ther mochemical estimate of the activation energy for SiH2 + CH4 is 59(+/- 12) k J mol(-1). Reasons for the greatly diminished reactivity of SiH2 with C-H a s compared with Si-H bonds are discussed. (C) 1999 John Wiley & Sons, Inc.