Anion stabilised hypercloso-hexaalane Al₆H₆

Boron hydride clusters are an extremely diverse compound class, which are of enormous importance to many areas of chemistry. Despite this, stable aluminium hydride analogues of these species have remained staunchly elusive to synthetic chemists. Here, we report that reductions of an amidinato-aluminium(III) hydride complex with magnesium(I) dimers lead to unprecedented examples of stable aluminium(I) hydride complexes, [(^ArNacnac)Mg]₂[Al₆H₆(Fiso)₂] (^ArNacnac = [HC(MeCNAr)₂]^-, Ar = C₆H₂Me₃-2,4,6 Mes; C₆H₃Et₂-2,6 Dep or C₆H₃Me₂-2,6 Xyl; Fiso = [HC(NDip)₂]^-, Dip = C₆H₃Prⁱ₂-2,6), which crystallographic and computational studies show to possess near neutral, octahedral hypercloso-hexaalane, Al₆H₆, cluster cores. The electronically delocalised skeletal bonding in these species is compared to that in the classical borane, [B₆H₆]^2-. Thus, the chemistry of classical polyhedral boranes is extended to stable aluminium hydride clusters for the first time.