Siloxane, Phosphate, and Hypervalent Formation in Cyclic Silicon and Phosphorus Reactions

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Abstract
Comparative reactions of phosphites and chlorosilanes with diols, S[R1R2C6H2OH]2, capable of forming eight-membered ring systems, were studied. With (CH2)4SiCl2 a bicyclic silane formed, S[R1R2C6H2O]4, whereas with SiC14, a hydrolysis reaction dominated yielding a cyclic disiloxane product, {(S[(t-Bu)2C6H2O]2-Si(OCH2CF3)} 20, whose X-ray structure showed a ∼50% displacement toward a trigonal bipyramid from a tetrahedron due to a Si[sbnd]S interaction. Hydrolysis reactions also ensued in reactions of P(OXyl)3 and P(OCH2CF3)3 with diols giving acyclic and cyclic phosphates, respectively, e.g., S(Me2C6H2)2(OH)OP(O)(OXyl)2 and S[(t-Bu)-McC6H2O]2P(O)(OCH2CF3). With the rigorous exclusion of moisture, the diol reaction with P(OCH2CF3)3 led to a hexacoordinated structure, via a P[sbnd]S interaction, S[(t-Bu)MeC6H2O]2P(OCH2CF3)3, shown to be ∼70% displaced toward an octahedron from a square pyramid based on X-ray analysis. With P(NMe2)3, a bicyclic oxyphosphorane formed, [S(Me2C6H2O)2]2PNMe2, which showed no evidence for P[sbnd]S coordination. Hydrolysis processes in the case of phosphorus are shown to correlate with the nature of the leaving group and are proposed to involve a hexacoordinated intermediate.