Room-temperature dissociation of 1,2-dibromodisilenes to bromosilylenes.

A room-temperature dynamic equilibrium between dibromodisilenes and bromosilylenes has been demonstrated by taking advantage of the steric protection using the fused-ring bulky 1,1,3,3,5,5,7,7-octa-R-s-hydrindacen-4-yl (Rind) groups. Although the bromosilylenes cannot be directly observed by spectroscopic methods, the thermal homolytic cleavage of the Si═Si double bond has been confirmed by a pseudo-first-order kinetics for the trapping with bis(trimethylsilyl)acetylene and a crossover reaction using two kinds of Rind-substituted dibromodisilenes. The addition of 4-pyrrolidinopyridine (PPy) to the dibromodisilene leads to an equilibrium mixture between the dibromodisilene and a PPy adduct of bromosilylene, the latter being isolated and characterized. The substitution of the bromine atom in the dibromodisilene by the Grignard reagent is significantly accelerated by the addition of PPy.