PENTACOORDINATED MOLECULES .95. INFLUENCE OF PHOSPHORUS SULPHUR BONDING IN THE FORMATION OF OCTAHEDRALLY COORDINATED CYCLIC PENTAOXYPHOSPHORANES

Formation of new pentaoxyphosphoranes X[R1R2C6H2O]2P(OPh)3 (X = S, R1 = R2 = t-Bu for 1; X = S, R1 = t-Bu, R2 = Me for 2; X = S, R1 = R2 = Me for 3; X = CH2, R1 = R2 = t-Bu for 4) containing sulfur-bridged eight-membered rings was achieved by oxidative addition reactions of triphenyl phosphite with diols in the presence of N-chlorodiisopropylamine in yields ranging from 70 to 80%. 1 contains 0.5 mol of Et2O of crystallization. X-ray analysis of 1-3 revealed molecular structures having varying degrees of P-S bond formation, which results in distorted octahedral configurations. The P-S distances, 2.880(1) (3), 2.744(2) (2), and 2.640(2) angstrom (1), when included in a series with those of related cyclic oxyphosphoranes studied earlier, showed a uniform decrease which parallels a structural coordinate measuring the formation of an octahedron from a square pyramid, i.e., a trajectory proceeding from five-to six-coordinated phosphorus. The decrease in P-S distance along the series is attributable to an increase of electronic factors supplied by the alkyl substituents on the eight-membered ring, t-Bu > Me, and the electron-withdrawing ability of the appendent ligands, (OC6H4)2 > OCH2CF3 > OPh. H-1 and P-31 solution-state NMR data are also reported. The structures of 1-3 contrast with that for an analogous derivative S(Me2C6H2O)2P(OCH2CF3)3 (B), having the same sulfur-containing eight-membered ring which resides in a trigonal bipyramid with the ring located diequatorially and possessing no P-S bond (P-S = 3.504(3) angstrom). The results have important mechanistic implications for enzyme hydrolysis of phosphates at active sites having interacting sulfur residues. Oxyphosphorane 1 crystallizes in the triclinic space group P1BAR with a = 9.696(3) angstrom, b = 10.814(2) angstrom, c = 22.113(3) angstrom, alpha = 82.62(1)degrees, beta = 85.38(2)degrees, gamma = 88.08(2)degrees, and Z = 2. Oxyphosphorane 2 crystallizes in the monoclinic space group P2(1)/n with a = 12.853(3) angstrom, b = 15.484(4) angstrom, c = 19.081(6) angstrom, beta = 108.70(2)degrees, and Z = 4. Oxyphosphorane 3 crystallizes in the triclinic space group P1BAR with a = 8.757(2) angstrom, b = 10.047(1) angstrom, c = 17.614(3) angstrom, alpha = 103.88-degrees, beta = 100.69(2)degrees, gamma = 92.65(2)degrees, and Z = 2. The final conventional unweighted residuals are 0.056 (1), 0.031 (2), and 0.032 (3).