NUCLEOPHILIC-ADDITION OF CH, NH, AND OH BONDS TO THE PHOSPHADIAZONIUMCATION AND INTERPRETATION OF P-31 CHEMICAL-SHIFTS AT DICOORDINATE PHOSPHORUS CENTERS

The phosphadiazonium cation [MesNP](+) reacts quantitatively with the fluorenylide anion, MesNH2, and Mes*OH (Mes* = 2, 4, 6-tri-tert-buty lphenyl), resulting in formal insertion of the N-P moiety into the H-Y (Y = C, N, O) bonds. Specifically, reaction of MesNPCl with fluoreny llithium gives the aminofluorenylidenephosphine [crystal data: C31H38N P, monoclinic, P2(1)/c, a = 9.568(8) Angstrom, b = 24.25(2) Angstrom, c = 11.77(1) Angstrom, beta = 101.38(8)degrees, Z = 4]. Similarly, rea ction of [MesNP][GaCl4]s*NH2 gives the diaminophosphenium salt [Mes*N (H)PN(H)Mes][GaCl4] [crystal data: C36H60Cl4GaN2P, monoclinic, C2/c, a = 24.921(2) Angstrom, b = 10.198(4) Angstrom, c = 16.445(2) Angstrom , beta = 93.32(1)degrees, Z = 4], and reaction with MesOH gives the f irst example of an aminooxyphosphenium salt [MesN(H)POMes*][GaCl4]. I t is proposed that the reactions involve nucleophilic attack at phosph orus followed by a 1, 3-hydrogen migration from Y to N. Experimental e vidence for the formation of sigma-complex intermediates is provided b y the isolation of [MesNP-PPh(3)][SO3CF3] [crystal data: C37H44F3- NO 3P2S, triclinic, P1, a = 10.663(1) Angstrom, b = 19.439(1) Angstrom, c = 10.502(1) Angstrom, alpha = 103.100(7)degrees, beta = 113.311(7)deg rees, gamma = 93.401(7)degrees, Z = 2]. As part of the unequivocal cha racterization of the aminooxyphosphenium salt, detailed solid-state P- 31 NMR studies and CIAO calculations on the phosphenium cations have b een performed. Contrary to popular belief, the phosphorus shielding in dicoordinate cations is not caused by the positive charge but results from efficient mixing between the phosphorus lone pair and pi orbita ls.