Bulky triazenide complexes of alumino- and gallohydrides

Abstract

The sterically bulky triazenes DitopN(3)(H)pTol, DitopN(3)(H)Mes, DmpN(3)(H)pTol and DmpN(3)(H)Mes, where Ditop = 2,6-di-p-tolylphenyl, Dmp = 2,6-dimesitylphenyl, pTol = p-MeC(6)H(4) and Mes = 2,4,6-Me(3)C(6)H(2), have been prepared. The reactivity of these triazenide precursors with LiAlH(4) and, in the cases of DmpN(3)(H)pTol and DmpN(3)(H)Mes, LiGaH(4), with diethyl ether as the solvent, has been examined. All reactions were undertaken in a 1:1 ratio giving rise to a variety of aluminium and gallium complexes that either incorporate LiH with a metal to triazenide ratio of 1:1 or generate 'LiH-free' aluminohydrides with aluminium to triazenide ratios of 1:1 or 1:2 dependant on triazenide bulk. Increasing triazenide bulk from DitopN(3)pTol through to DmpN(3)Mes results in a transition from complexes of structure [{Li(OEt(2))(mu-H)(mu-L)AlH (mu-H)}(n)] (L = triazenide ligand; n = 2 DitopN(3)pTol, n = 1 DitopN(3)Mes, DmpN(3)pTol), to bis(triazenide) monohydride complexes [AlH(L)(2)], through to monotriazenide dihydride complexes [AlH(2)(L)]. By contrast, both DmpN(3)(H)Ar (Ar = pTol or Mes) triazenides react with LiGaH(4) to afford the monomeric, lithium hydride containing, complexes [Li(ether)(mu-H)(mu-L)GaH(2)] (L = triazenide, ether = OEt(2) or THF). The molecular structures of [AlH(DitopN(3)Mes)(2)], [AlH(DmpN(3)pTol)(2)], [AlH(2)(DmpN(3)Mes)(THF)] and [Li(THF)(mu-H)(mu-DmpN(3)Mes)GaH(2)] are reported, as well as the structure of the triazene DmpN(3)(H)Mes which exists in the E-syn isomeric form in the solid-state.