HEXACOORDINATION VIA SULFUR DONOR ACTION IN NITROGEN AND CHLORINE BONDED BICYCLIC TETRAOXYPHOSPHORANES

Oxidative addition reactions of a quinone with the sulfur containing c yclic chlorophosphine S[(t-Bu)-MeC(6)H(2)O]2PCl (1) yielded the new bi cyclic tetraoxyphosphoranes, S[(t-Bu)MeC(6)H(2)O]2PCl(O2C6Cl4) (2) and S[(t-Bu)MeC(6)H(2)O]2PCl(O2C6Cl4) (5) Further new derivatives of this class were prepared by chlorine displacement reactions of 2 and 5 to give S[(t-Bu)MeC(6)H(2)O]P-2(NHC(6)H(4)Me)(O2C6Cl4) (3), S[(t-Bu)MeC(6 )H(2)O]P-2(NMe(2))(O2C6Cl4) (4), S[(t-Bu)MeC(6)H(2)O]P-2(NHCH2C6H5)(O2 C14H8) (6), and S[(t-Bu)MeC(6)H(2)O]P-2(NMe(2))(O2C14H8) (7). X-ray st udies of 2-6 revealed hexacoordination due to donor action by sulfur w hich is present as part of an eight-membered ring system. The series 2 -6 formed geometries that were displaced along a coordinate from a squ are pyramid to an octahedron, ranging from 24% to 71%. The respective P-S distance decreased along this series from 3.04 to 2.48 Angstrom as the octahedral character increased. Increased P-31 NMR shielding acco mpanied the chloro derivatives 2 and 5, while increased pi P-N back-bo nding resulted in the least shielded members 4, 6, and 7 containing th e less electronegative nitrogen atom. These changes in P-31 chemical s hift correlate with the extent of octahedral character where the more shielded phosphorus atom has the greater octahedral character. The ana lysis allows a lower limit in the phosphorus atom electrophilicity to be established that will allow hexacoordination in this series of bicy clic tetraoxyphosphoranes provided by a variation in ligand properties .