In accord with the CGMT model, tetrasilyldimetallenes [[([H.sub.3]Si).sub.2]E=E(Si[H.sub.3]).sub.2], E = Si, Ge, and Sn] whose component silylene [([H.sub.3]Si).sub.2]E: has smaller [DELTA][E.sub.ST] than the corresponding [H.sub.2]E: are shown theoretically to be planar around the E=E bond.
(4a),(23) The dissociation of 16 into a pair of the corresponding silylene is evidenced by trapping of the silylene with alkenes and acetylenes.
(38) Because silylene 31 is divalent and highly reactive though it is sterically protected, versatile thermal and photochemical reactions of 31 have been observed.
The first compound with cumulative Si=Si double bonds, trisilaallene 34a, was synthesized starting with stable silylene 31.
Dimerization of a silylene to the corresponding disilene and its reverse reaction constitute an important pair of chemical processes in organosilicon chemistry.
As a conjugated siladiene, tetrasila-1,3-diene 52 is synthesized as airsensitive red crystals in 13% yield by the reaction of silylene 31 with [Me.sup.3]SiSi[Br.sup.3] giving tribromodisilane 53 followed by the reduction with sodium metal in toluene at room temperature (eq [23]).
Because 57 (38),(57) and 58 (58) are known as major products of the thermal and photochemical reactions of silylene 31 in benzene, respectively, the initial step of these reactions should be the cleavage of a Si=Si double bond of 52 into 59 and 31 (eq [26]).
The dihedral angle in silylene 63 is significantly increased by the steric effects of bulky isopropyl substituents, and hence, the [DELTA][E.sup.ST] value is reduced to 54.3 kcal [mol.sup.-1]; the bridged dimer of 63 is higher in energy by 16.0 kcal [mol.sup.-1] than the Si-Si bonded dimer 65.
(2004) Isolable silylene, disilenes, trisilaallene, and related compounds.
Both stereorigid catalysts Et[[Ind].sub.2]Zr[Cl.sub.2]/MAO, analogous
silylene bridged catalysts [Me.sub.2]Si[[Ind].sub.2] Zr[Cl.sub.2]/MAO,
silylene bridged [Me.sub.2]Si[[2-MeInd].sub.2]Zr[Cl.sub.2] catalysts as well as the nonstereospecific catalyst [[Ind].sub.2]Zr[Cl.sub.2]/MAO were used in the polymerizations.
They are organized into sections on the chemistry of organosilicon-based reactive intermediates, different aspects of molecular inorganic silicon chemistry, the basic chemistry of silicon in the coordination sphere of transitional metals (this includes such topics as
silylene complexes, catalysis, and silicon-metal bonds), the role of silicon in organic and bioorganic chemistry, complex systems of organosilicon compounds in and for industrial applications, and solid silicon-based materials.