CRYSTAL-STRUCTURES OF 2 N-METHYLTRIPHENYLPHOSPHORANIMINES - TRIPHENYLPHOSPHINE-N-METHYLIMINE BORANE, PH,PN(CH,)BH, AND N,N-DIMETHYLAMINOTRIPHENYLPHOSPHONIUM TETRAFLUOROBORATE, [PH(3)PN(CH3)(2)](-()BF4)

X-ray crystal structure determinations of two N-methyltriphenylphospho ranimines, Ph(3)PN(CH3)BH3 (1) and [Ph(3)PN(CH3)(2)](BF4-)-B-+ (2), we re carried out to determine the effects of pi-bonding between P and N in triphenylphosphoranimines, Ph(3)P=NR, as a function of formal charg e on the N atom. Crystals of 1 are monoclinic, space group P2(1)/n wit h a = 11.370(2), b = 10.507(2), c = 14.360(4) Angstrom and beta = 91.4 7(2)degrees with Z = 4. Bond lengths of interest are: P-N 1.605(3), N- B 1.583(5), N-C 1.456(5), average P-C(phenyl) 1.805(3) Angstrom. Bond angles of interest are: P-N-C 124.2(2), P-N-B 120.7(2), C-N-B 114.6(3) , average C-P-C 106.8(5), average C-P-N of 112.0(5)degrees. Crystals o f 2 are monoclinic, space group P2(1)/c with a = 16.379(3), b = 16.777 (2), c = 14.481(2) Angstrom and beta = 94.41(1)degrees with Z = 8 (2 m olecules per asymmetric unit). Average bond lengths of interest are: P -N 1.626(4), P-C(phenyl) 1.795(7), N-C 1.442(13) Angstrom. Average bon d angles are: C-P-C 109(2), C-P-N 110(2), P-N-C 123(3), C-N-C 112.8(4) degrees. The longer P-C distances, the shorter P-N distance and smalle r CP-C angles in 1 compared to 2 are consistent with changes in the s- character around the P atoms.