Structure-Reactivity Relationships for Associative Displacement Reactions of Penta- and Hexacoordinate Cyclic Oxyphosphoranes with Catechols(1)(,)(2).

The reactivity of a series of cyclic pentaoxyphosphoranes containing a sulfonyl group was carried out, O(2)S(t-Bu)MeC(6)H(2)OP(OCH(2)CF(3))(3) (1), O(2)S(t-Bu)MeC(6)H(2)OP(OPh)(3) (2), O(2)S(t-Bu)(2)C(6)H(2)OP(OCH(2)CF(3))(3) (4), and O(2)S(t-Bu)(2)C(6)H(2)OP(OPh)(3) (5). Also included were derivatives containing sulfur, S(t-Bu)MeC(6)H(2)OP(OPh)(3) (6) and S(t-Bu)(2)C(6)H(2)OP(OPh)(3) (8), and the methylene group, CH(2)(t-Bu)MeC(6)H(2)OP(OPh)(3) (7), in place of the sulfonyl group in the ring-containing component. (31)P NMR monitoring of the reactions of the oxyphosphoranes with catechol and 4-nitrocatechol shows the following order of reactivity: 7 > 8 > 6 > 2 > 5 >> 1. It is established that the reactions are associative. An analysis of the products formed is given relative to this mechanistic process. Both 1 and 4 are found to be inert toward nucleophilic displacement by the catechols employed. It is suggested that the looseness of P-O bonds (implied by their increased length) that reside in either octahedral formulations or in axial positions of a trigonal biyramid is the principal factor associated with reactivity for these cyclic oxyphosphoranes. For the hexacoordinated geometries, the order of reactivity parallels the extent of octahedral character: 8 > 6 > 2 > 5.