THERMAL-DISSOCIATION OF DISILENES INTO SILYLENES

Extremely hindered and stable disilenes (Tbt(Mes)Si=Si(Mes)Tbt {Tbt=2, 4,6-tris[bis(trimethylsilyl)methyl]phenyl, Mes=2,4,6-trimethylphenyl. (Z)-1: cis-isomer, (E)-1: trans-isomer}) underwent dissociation under very mild conditions (ca. 70 degrees C) into a divalent silicon specie s (Tbt(Mes)Si: (2)), which was trapped by methanol, triethylsilane, 2, 3-dimethyl-1,3-butadiene, elemental sulfur, and elemental selenium to afford the corresponding adducts in good yields. Silylene 2 reacted wi th some carbon-carbon multiple-bond compounds to afford the correspond ing [1+2] cycloadducts, among which the adduct with 3,3,6,6-tetramethy lthiacyclohept-4-yne was established by an X-ray diffraction analysis. Silylene 2 also reacted with naphthalene and benzene to give the corr esponding adducts, 15 and 17, respectively, the molecular structures o f which were confirmed by X-ray crystallographic analyses. The formati on of 15 and 17 represents the first example of [1+2] cycloaddition of silylenes to aromatic compounds. The thermolysis of 15 and 17 regener ated silylene 2, which was trapped with triethylsilane. A kinetic stud y of the thermal dissociation of 1 gave the activation parameters, whi ch were compared with those for E reversible arrow Z isomerization of previously reported disilenes.