Catalytic dehydrogenation condensation of silyl hydrides and amines: thermal decomposition of silazanes and polysilazanes

摘要

The synthesis of silazanes by the condensation of silyl hydrides and amines or ammonia has been shown to be catalyzed by palladium chloride or ruthenium dodecacarbonyl. The synthesis of diaminosilanes can also be catalyzed by the same catalysts. Attempts to prepare disilazanes from rtriethylsilane and butylamine were not successful;The synthesis of polysilazanes was shown to be possible at room temperature when palladium chloride was used as the catalyst. Ruthenium dodecacarbonyl was not useful under these conditions. The molecular weight of the polysilazane is dependent upon the rate of ammonia addition to the silane solution. When trihydrosilanes were condensed with ammonia no silicon hydrogen bonds remained in the polymer indicating that extensive crosslinking had occurred;The generation of silanimines is possible by the retroene elimination of propene from allylsilazanes. The rates of propene formation vary significantly with the position of the allyl group on the silazane. When the allyl group is on the nitrogen in disilazanes propene is formed by a concerted elimination and by homolysis of the nitrogen allyl bond. When the allyl group is on silicon in disilazanes propene is formed by the concerted elimination of propene. No evidence was found for homolysis of the silicon allyl bond;The [beta] elimination of methoxysilanes from trisilazanes was investigated. The reaction has a log A of 14.0 which suggests that the transition state for this reaction is very polar;The [alpha] elimination of hexamethyldisiloxane from N,N,O-tris(trimethylsilyl)hydroxyamine does not occur under flash vacuum conditions. Instead a zwitterionic intermediate leads to a migration of a methyl anion to form (trimethylsilyl(methyl)amino) pentamethyldisiloxane;The decomposition of polysilazanes with an allyl group on silicon resulted in a ceramic char containing large amounts of carbon. Analysis of the volatile organics that are produced in such polysilazanes showed that methane was the major product. Propene and ethane were formed in low yields. ftn*DOE Report IS-T-1362. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy.