PENTACOORDINATED MOLECULES .92. DIEQUATORIAL AND AXIAL EQUATORIAL ORIENTATIONS OF 8-MEMBERED RINGS IN MONOCYCLIC PENTAOXYPHOSPHORANES CONTAINING TRIFLUOROETHOXY GROUPS

Reaction of (CF3CH2O)3P with diols yielded new monocyclic pentaoxyphosphoranes with eight-membered ring systems containing methylene or sulfur bridges. Trigonal-bipyramid (TBP) geometries were shown to be present by X-ray analysis for CH2(C6H4O)2P(OCH2CF3)3 (2) and S(Me2C6H2O)2P(OCH2CF3)3 (3) with the ring in 2 located in axial-equatorial (a-e) positions and the ring in 3 in diequatorial (e-e) sites. These structures are compared with the first pentaoxyphosphorane derivative to exhibit a diequatorial ring in a TBP, CH2[Me(t-Bu)C6H2O]2P(OCH2CF3)3 (1), recently prepared in our laboratory. A pseudooctahedral structure was revealed by X-ray analysis for S[(t-Bu)2C6H2O]2P(OCH2CF3)3 (4). H-1, P-31, and F-19 solution NMR data indicated rapid intramolecular ligand exchange for 2 and 3 at room temperature. In contrast, NMR data on 1 and 4, which contained tert-butyl groups, did not indicate exchange behavior. Here, retention of the basic solid-state TBP in solution was consistent with the observed spectra. Comparison of solid-state P-31 NMR spectra with solution P-31 NMR data of 3 and 4 suggested retention of their basic solid-state geometries in solution. Comparisons with related pentaoxyphosphoranes having six- and seven-membered rings suggest that seven- and eight-membered rings are more easily accommodated in diequatorial positions compared to positioning saturated six-membered rings in this location of a TBP. Oxyphoshorane 2 crystallizes in the triclinic space group P1BAR with a = 9.712 (2) angstrom, b = 11.039 (3) angstrom, c = 12.521 (2) angstrom, alpha = 97.48 (2)-degrees, beta = 111.77 (1)-degrees, gamma = 110.56 (2)-degrees, and Z = 2. Derivative 3 crystallizes in the triclinic space group P1BAR with a = 9.245 (2) angstrom, b = 12.464 (2) angstrom, c = 12.891 (2) angstrom, alpha = 76.77 (1)-degrees, beta = 74.69 (2)-degrees, gamma = 70.60 (1)-degrees, and Z = 2. Oxyphosphorane 4 crystallizes in the triclinic space group P1BAR with a = 11.202 (2) angstrom, b = 11.307 (4) angstrom, c = 16.372 (8) angstrom, alpha = 99.66 (3)-degrees, beta = 94.39 (3)-degrees, gamma = 103.42 (2)-degrees, and Z = 2. The final conventional unweighted residuals are 0.050 (2), 0.075 (3), and 0.076 (4).