SILOXANE, PHOSPHATE, AND HYPERVALENT FORMATION IN CYCLIC SILICON AND PHOSPHORUS REACTIONS

Comparative reactions of phosphites and chlorosilanes with diols, S[R(1)R(2)C(6)H(2)OH](2), capable of forming eight-membered ring systems, were studied. With (CH2)(4)SiCl2 a bicyclic silane formed, S[R(1)R(2)C(6)H(2)O]Si-2(CH2)(4), whereas with SiCl4, a hydrolysis reaction dominated yielding a cyclic disiloxane product, (S[(t-Bu)(2)C6H2O](2)- Si(OCH2CF3)]O-2, whose X-ray structure showed a similar to 50% displacement toward a trigonal bipyramid from a tetrahedron due to a Si-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 (Me(2)C(6)H(2))(2)(OH)OP(O) (OXyl)(2) and S [(t-Bu)-MeC(6)H(2)O]P-2(O)(OCH2CF3). With the rigorous exclusion of moisture, the diol reaction with P(OCH2CF3)(3) led to a hexacoordinated structure, via a P-S interaction, S[(t-Bu)MeC(6)H(2)O]P-2(OCH2CF3)(3), shown to be similar to 70% displaced toward an octahedron from a square pyramid based on X-ray analysis. With P(NMe(2))(3), a bicyclic oxyphosphorane formed, [S(Me(2)C(6)H(2)O)(2)](2)PNMe(2), which showed no evidence for P-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.