HYPERVALENT PHOSPHORUS COMPOUNDS WITH SULFUR-CONTAINING EIGHT-MEMBERED RINGS. NATURE OF THE LEAVING GROUP ON HYDROLYSIS TO ACYCLIC VS CYCLIC PHOSPHATES

Abstract

Reactions of phosphites with diols in the presence of N-chlorodiisopropylaminc in ether solution led to new compounds formulated as the bicyclic tetraoxyphosphorane, [S(Me₂C₆H₂O)₂]₂PNMe₂ (1), the hexacoordinated pentaoxyphosphorane, S[(t-Bu)₂C₆H₂O]₂(Me₂C₃H₄O₂)(OCH₂CF₃) (2), with a P—S interaction indicated by ³P NMR, and the two phosphates, {(CH₃CH₂CH₂)(CH)[t-Bu)₂C₆H₂OH]₂}₂P(O)(OCH₂CF₃) (3) and S(Me₂C₆H₂)₂(OH)OP(O)(OXyl)₂ (4), resulting from hydrolysis reactions. The X-ray structures of 1 and 4 were obtained, and all were characterized by NMR spectral measurements in solution. Phosphorane 1 possessed a trigonal bipyramidal geometry displaced 29% toward a rectangular pyramid. The lack of P—S coordination, potentially available from the two attached eight-membered ring systems, is attributable to strong P—N π bonding. X-ray analysis shows 4 to form as an acyclic phosphate rather than a cyclic phosphate. This is attributed to the presence of the poor OXyl leaving group. It is proposed that the hydrolysis process leading to acyclic and cyclic phosphates proceeds by way of a hexacoordinated intermediate that forms as a result of P—S coordination. Phosphorane 1 crystallizes in the monoclinic space group C2/c with a = 26.034(5) Å, b = 15.230(2)Å c = 24.687(2) Å, β = 131.31(1)°, and Z = 8. Phosphate 4 crystallizes in the monoclinic space group P2₁/c with a = 12.971 (4) Å, b = 22.572(3) Å, c = 10.800(2) Å, β = 109.25(2)°, and Z = 4. The final conventional unweighted residuals are 0.059 (1) and 0.035 (4).