Kinetic studies on Brook-type isomerization of acylpolysilanes to silenes

First-order rate constants of Brook-type isomerization of acylpolysilanes (Me3Si)3SiCOR (R = iso-Pr, tert-Bu, Ad, 2,6-xylyl, and Mes) leading to silenes (Me3Si)2Sidouble bond; length as m-dashC(OSiMe3)R at various temperatures were determined. Their Eyring plots gave kinetic parameters of ΔH‡ = 26.6–29.4 kcal mol−1 and ΔS‡ = −11.5 to −14.6 cal mol−1 K−1. The isomerization was accelerated by introducing an electron-donating alkyl substituent on the carbonyl carbon. These results are in accordance with a concerted mechanism involving a four-centered transition state.