the extent of sequential reduction desired the fluorohalodisilanes which are preferred materials for selective reduction by the method of this invention can be obtained for example from the reactions of difluorosilylene with a hydrogen halide shown below specifically for reaction with hbr str1 reaction 3 corresponds to the redistribution of the principal product of the reaction sif 2 hsif 2 br further illustrating the reduction of preferred fluorohalodisilanes trialkyltin hydride or dialkyltin dihydride reacts with for example sif 3 sihbr 2 in the liquid phase to produce a fluorodisilane of the formula si 2 f x h 6 x where x is 3 for example str2 thus according to the present invention the trialkyltinhydride or dialkyltin dihydride reduces the si br bonds of sif 3 sihbr 2 to form essentially sif 3 sih 3 without affecting the si si or si f bonds additionally when the reaction is conducted at low temperatures the product of the first reduction step sif 3 sih 2 br can readily be detected a comparable reaction with a commonly used reducing agent vitride u2122 naalh 2 och 2 ch 2 och 3 2 conducted under similar conditions resulted in both the si br and si f bonds being reduced producing sih 4 sif 3 h and sif 4 silicon silicon bonds were destroyed since there were no disilanes.