Structure-reactivity relationships for associative displacement reactions of penta- and hexacoordinate cyclic oxyphosphoranes with catechols

The reactivity of a series of cyclic pentaoxyphosphoranes containing a sulfonyl group was carried out, O2S[(t-Bu)MeC6H2O](2)P(OCH2CF3)(3) (1), O2S[(t-BU)MeC6H2O](2)P(OPh)(3) (2), O2S[(t-BU)(2)C6H2O](2)P(OCH2CF3)(3) (4),and O2S [(t-Bu)(2)C6H2O](2)P(OPh)(3) (5). Also included were derivatives containing sulfur, S[(t-Bu)MeC6H2O](2)P(OPh)(3) (6) and S[(t-Bu)(2)C6H2O](2)P(OPh)(3) (8), and the methylene group, CH2[(t-Bu)MeC6H2O](2)P(OPh)(3) (7), in place of the sulfonyl group in the ring-containing component. P-31 NMR monitoring of the reactions of the oxyphosphoranes with catechol and 4-nitrocatechol shows the following order of reactivity: 7 > 8 > 6 > 2 > 5 much greater than 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.