Synthesis, Structure, and Stability of Adducts between Phosphide and Amide Anions and the Lewis Acids Borane, Tris(pentafluorophenyl)borane, and Tris(pentafluorophenyl)alane

The phosphinoborane adduct H3P·B(C6F5)3 can be deprotonated using LiN(SiMe3)2 to give the phosphidoborate salt Li[H2PB(C6F5)3], which was converted to the phosphidodiborates Li[H2P{B(C6F5)3}2] and Li[H2P{B(C6F5)3}{BH3}] by treatment with an equivalent of B(C6F5)3 or Me2S·BH3, respectively. A series of anions of the form [RR′P{M(C6F5)3}{BH3}]−, where R = R′ = Ph or R= tBu, R′ = H, and M = B or Al, were prepared (through treatment of salts Li[RR′P(BH3)] with the corresponding Lewis acid) and characterized using multinuclear NMR, elemental analysis and X-ray crystallography. The solid state structures of [Li(Et2O)x][Ph2P{M(C6F5)3}{BH3}] exhibit η2-bonding of the BH3 group to the cationic lithium center. The attempted preparation of an analogous series with amide cores of the form [R2N{B(C6F5)3}{BH3}]− proved unsuccessful; among the competing reaction pathways hydride abstraction occurred preferentially to yield Li[HB(C6F5)3] and dimers or higher oligomers with the composition (R2NBH2)n.