KINETIC-STUDY ON THERMAL SYN-ANTI ISOMERIZATION OF DODECAISOPROPYLTRICYCLO[4.2.0.0(2,5)]OCTASILANE

When heated at 493 K, yn-dodecaisopropyltricyclo[4.2.0.0(2,5)]octasila ne (syn-1) isomerizes to ti-dodecaisopropyltricyclo[4.2.0.0(2,5)]octas ilane (anti-1); isomerization of anti-1 to syn-1 does not occur at 493 K. Thermodynamic parameters were determined for the one-way isomeriza tion of syn-1 to anti-1: E(a) = 42.3 kcal mol(-1), log A = 15.1 s(-1), Delta H double dagger = 41.4 kcal mol(-1), Delta S double dagger = 7. 6 X 10(-3) kcal mol(-1) K-1 and Delta G(493K)double dagger = 37.6 kcal mol(-1). The activation energy is considerably larger than that for t he analogous thermal isomerization of syn-bicyclo[4.2.0.0(2,5)]octane (syn-2) to anti-tricyclo[4.2.0.0(2,5)]octane (anti-2), indicating that the bond dissociation energy of the bridgehead Si-Si bond of syn-1 is larger than that of the bridgehead C-C bond of syn-2.