Bulky triazenide complexes of alumino- and gallohydrides

Abstract

The sterically bulky triazenes DitopN₃(H)pTol, DitopN₃(H)Mes, DmpN₃(H)pTol and DmpN₃(H)Mes, where Ditop = 2,6-di-p-tolylphenyl, Dmp = 2,6-dimesitylphenyl, pTol = p-MeC₆H₄ and Mes = 2,4,6-Me₃C₆H₂, have been prepared. The reactivity of these triazenide precursors with LiAlH₄ and, in the cases of DmpN₃(H)pTol and DmpN₃(H)Mes, LiGaH₄, 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 DitopN₃pTol through to DmpN₃Mes results in a transition from complexes of structure [{Li(OEt₂)(μ-H)(μ-L)AlH (μ-H)}_n] (L = triazenide ligand; n = 2 DitopN₃pTol, n = 1 DitopN₃Mes, DmpN₃pTol), to bis(triazenide) monohydride complexes [AlH(L)₂], through to monotriazenide dihydride complexes [AlH₂(L)]. By contrast, both DmpN₃(H)Ar (Ar = pTol or Mes) triazenides react with LiGaH₄ to afford the monomeric, lithium hydride containing, complexes [Li(ether)(μ-H)(μ-L)GaH₂] (L = triazenide, ether = OEt₂ or THF). The molecular structures of [AlH(DitopN₃Mes)₂], [AlH(DmpN₃pTol)₂], [AlH₂(DmpN₃Mes)(THF)] and [Li(THF)(μ-H)(μ-DmpN₃Mes)GaH₂] are reported, as well as the structure of the triazene DmpN₃(H)Mes which exists in the E-syn isomeric form in the solid-state.