Magnesium(I) Reduction of Aluminum(III) Hydride Complexes: Generation of Mixed Valence Aluminum (Al /Al ) Hydride Cluster Compounds, [Al H (NR ) {Mg(β-diketiminate)} ].

Reduction of a range of amido- and aryloxy-aluminum dihydride complexes, e.g. [AlH (NR ){N(SiMe ) }] (NR =NMe or N-methylpiperidine (NMP)), with β-diketiminato dimagnesium(I) reagents, [{( Nacnac)Mg} ] ( Nacnac=[HC(MeCNAr) ] , Ar=mesityl (Mes) or 2,6-xylyl (Xyl)), have afforded deep red mixed valence aluminum hydride cluster compounds, [Al H (NR ) {Mg( Nacnac)} ], which have an average Al oxidation state of +0.66, the lowest for any well-defined aluminum hydride compound. In the solid-state, the clusters are shown to have distorted octahedral Al cores, having zero-valent Al axial sites and mono-valent AlH equatorial units. Several novel by-products were isolated from the reactions that gave the clusters, including the Mg-Al bonded magnesio-aluminate complexes, [( Nacnac)(Me N)Mg-Al(μ-H) [{Mg( Nacnac)} (μ-H)]]. Computational analyses of one aluminum hydride cluster revealed its Al core to be electronically delocalized, and to possess one unoccupied, and six occupied, skeletal molecular orbitals.