New aspects of low-coordinated organosilicon compounds: Thermal dissociation of disilenes into silylenes

Disilenes Tbt(Mes)Si=SiTbt(Mes)(Mes:mesityl) bearing an efficient steric protection group, 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl(Tbt), were synthesized and found to be extremely stable toward oxygen and water. In spite of the stability, they underwent thermal dissociation into silylenes under very mild conditions (ca. 50’ C). Silylenes thus formed reacted with alkenes, alkynes, benzene, naphthalene, nitrile, phosphaalkyne, carbon disulfide, and isonitriles to give a variety of interesting carboand heterocycles, most of which are new types of compounds. Kinetic studies on the thermal dissociation were also carried out and the kinetic parameters were compared with those for E-Z isomerization of known disilenes. INTRODUCTION Since the first isolation of a stable disilene, tetramesityldisilene, by West et al. in 1981 (l), remarkable progress has been witnessed in the chemistry of low-coordinated compounds of heavier group 14 elements, which have been synthesized by kinetic stabilization using sterically bulky substituents. In continuation of our work on low-coordinated compounds of gorup 14 elements, we undertook the synthesis of a very stable disilene by taking advantage of an efficient steric protection group, 2,4,6tris[bis(trimethylsilyl)methyl]phenyl (denoted as Tbt), which was developed by us. We have already succeeded in the synthesis of stable silanethione, germanethione, germaneselone, and stannanethione with the Tbt group as a steric protection group (2). In this paper we report the synthesis of extremely stable disilenes 1 and their thermal dissociation into silylenes, Tbt(Mes)Si(Z).