Synthesis of a stable adduct of dialane(4) (Al2H4) via hydrogenation of a magnesium(I) dimer

The desorption of dihydrogen from magnesium(H) hydride, MgH2 (containing 7.6 wt% H), is reversible. MgH2 therefore holds promise as a hydrogen storage material in devices powered by fuel cells. We believed that dimeric magnesium(I) dimers (LMgMgL, L = beta-diketiminate) could find use as soluble models to aid the study of the mechanisms and/or kinetics of the hydrogenation of magnesium and its alloys. Here, we show that LMgMgL can be readily hydrogenated to yield LMg(mu-H)(2)MgL by treatment with aluminium(III) hydride complexes. In one case, hydrogenation was reversed by treating LMg(mu-H)(2)MgL with potassium metal. The hydrogenation by-products are the first thermally stable, neutral aluminium(II) hydride complexes to be produced, one of which, [{(IPr)(H)(2)Al}(2)] (IPr = :C[{(C6H3-i-Pr-2-2,6)NCH}(2)]), is an N-heterocyclic carbene adduct of the elusive parent dialane(4) (Al2H4). A computational analysis of this compound is presented.