SYNTHESES, STRUCTURES, AND SPECTROSCOPIC STUDIES OF SEVERAL NEW CLASSES OF COMPOUNDS HAVING BORON ARSENIC BONDS

Several new arsinoboranes, wherein boron and arsenic are three coordin ate, have been prepared and characterized. They are analogous to B-N a nd B-P species in which p-p pi-bonding, involving the pnictide lone pa ir and the empty boron p-orbital, may occur. The main conclusion of th ese studies is that B-As pi-bonding, although inherently strong, is di fficult to achieve because of the larger inversion barrier at arsenic. Nontheless, very electropositive or bulky substituents at arsenic red uce this barrier sufficiently to observe substantial B-As pi-interacti ons. The compounds studied include [PhB(Cl)As(t-Bu)2]2 (1), PhB{As(t-B U)212 (2), CpB(Cl)As(t-Bu)2 (3), (C20H30)BAs(t-Bu)2 (4), Mes2BAsPhLi( THF)3 (5), [Mes2BAsPh] [Li(TMEDA)2] (6), and Mes2BAs(Ph)SiMe3 (7) (Cp = pentamethylcyclopentadienyl, TMEDA = N,N,N'N'-tetramethylenediamine , Mes = 2,4,6-Me3C6H2). The species 5 and 6 have been reported in a pr eliminary note. All compounds were characterized by X-ray crystallogra phy and H-1 NMR and B-11 NMR spectroscopy. In addition, 5 and 7 were c haracterized by variable-temperature H-1 NMR studies.