Synthesis of Functional Monosilanes by Disilane Cleavage with Phosphonium Chlorides

The Müller-Rochow direct process (DP) for the large-scale production of methylchlorosilanes Me_n SiCl_4-n (n=1-3) generates a disilane residue (Me_n Si₂ Cl_6-n , n=1-6, DPR) in thousands of tons annually. This report is on methylchlorodisilane cleavage reactions with use of phosphonium chlorides as the cleavage catalysts and reaction partners to preferably obtain bifunctional monosilanes Me_x SiH_y Cl_z (x=2, y=z=1; x,y=1, z=2; x=z=1, y=2). Product formation is controlled by the reaction temperature, the amount of phosphonium chloride employed, the choice of substituents at the phosphorus atom, and optionally by the presence of hydrogen chloride, dissolved in ethers, in the reaction mixture. Replacement of chloro by hydrido substituents at the disilane backbone strongly increases the overall efficiency of disilane cleavage, which allows nearly quantitative silane monomer formation under comparably moderate conditions. This efficient workup of the DPR thus not only increases the economic value of the DP, but also minimizes environmental pollution.