DIRECT OBSERVATION OF PHOSPHORANIDE ANIONS - EXTREMELY STABLE P-H DIOXYPHOSPHORANES CONTAINING 2 C-P BONDS

Two very stable P-H phosphoranes, 13 and 19, each containing two aryl and two alkoxy ligands, are prepared by LiAlH4 reduction of spirobicyclic phosphonium salt 12 or reaction of PCl3 with the Grignard reagent made from bromo alcohol 18, respectively. Evidence is presented for the intermediate formation of tetracoordinate trigonal bipyramidal phosphoranide anions, conjugate bases of the P-H phosphoranes, in these syntheses. The phosphoranide anions 9 and 24, produced by deprotonation of P-H phosphorane 13 or 19 with LiAlH4, are directly observed by H and 31P NMR spectroscopy. Phosphoranide 9 is alkylated by benzyl bromide to give phosphorane 17. The lithium derivative of phosphoranide 9 is not air sensitive but the sodium derivative is rapidly air oxidized to give the sodium phosphoranoxide 7. The P-H phosphoranes (13 and 19) are not oxidized by H2O2 in CHCl3, in contrast to the easy oxidation of tetraoxy or tetraaryl P-H phosphoranes, suggesting that essentially none of the open-chain tricoordinate phosphorus tautomers are in equilibrium with the P-H phosphoranes. We present 1H, 19F, and 31P NMR, infrared spectroscopic, and mass spectrometric data in support of these findings. © 1979, American Chemical Society. All rights reserved.