PENTACOORDINATED MOLECULES .88. BOAT AND CHAIR FORMS FOR SULFUR-CONTAINING CYCLIC OXYPHOSPHORANES

Oxidative-addition reactions of pentafluorophenol or phenanthrenequinone to cyclic phosphites resulted in the formation of the new cyclic phosphoranes (Me2C3H4O2)P(OC6F5)2(S-Xyl) (1), (C3H6S2)P(OC6F5)2(O-Xyl) (2), and (C2H4S2)P(O2C14H8)(O-Xyl) (3). The monocyclic derivative 1 is unique in having the phosphorinane ring -n a chair conformation at axial-equatorial sites of a trigonal bipyramid (TBP). Previously, boat forms were found at this location unless hydrogen bonding was present. Further, the ring in 1 has equal P-O axial and equatorial bond lengths, representing the first observance of this kind in pentacoordinate phosphorus chemistry. A combination of an electronegativity effect ascribed to the pentafluorophenyl groups and a steric contribution in the molecule is suggested as responsible for the uniqueness of 1. Both 2 and 3 have TBP structures with the thiophosphorinane ring in 2 residing in a twisted-boat conformation and the sulfur-containing five-membered ring of 3 present in an envelope conformation. Both rings are located at axial-equatorial sites. H-1 NMR spectra reveal that 1 undergoes rapid pseudorotation at room temperature involving axial-equatorial ring interchange, which is "stopped" at -65-degrees-C. Most likely 2 is nonrigid similar to 1. The H-1 NMR spectra of 3 are invariant from 20 to -90-degrees-C, showing nonrigid behavior indicating axial-equatorial to diequatorial activation for the phenanthrene ring in a pseudorotational process allowing equivalence of all four methylene protons of the sulfur-containing five-membered saturated ring. The monocyclic derivative 1 crystallizes in the triclinic space group P1BAR with a = 11.239 (11) angstrom, b = 11.288 (5) angstrom, c = 11.934 (8) angstrom, alpha = 74.72 (5)-degrees, beta = 65.34 (6)-degrees, gamma = 74.58 (6)-degrees, and Z = 2. The monocyclic derivative 2 crystallizes in the monoclinic space group P2(1)/c with a = 14.485 (5) angstrom, b = 10.573 (4) angstrom, c = 16.626 (3) angstrom, beta = 99.85 (2)-degrees, and Z = 4. Spirocyclic 3 crystallizes in the monoclinic space group P2(1)/c with a = 13.493 (2) angstrom, b = 9.048 (3) angstrom, c = 18.149 (6) angstrom, beta = 96.86 (2)-degrees, and Z = 4. The final conventional unweighted residuals are 0.095 (1), 0.036 (2), and 0.044 (3).