Magnesium(I) Reduction of Aluminum(III) Hydride Complexes: Generation of Mixed Valence Aluminum (Al^I/Al⁰) Hydride Cluster Compounds, [Al₆H₈(NR₃)₂{Mg(β‐diketiminate)}₄]**

Abstract

Reduction of a range of amido-and aryloxyaluminum dihydride complexes, e.g. [AlH 2 (NR 3 ){N-(SiMe 3 ) 2 }] (NR 3 = NMe 3 or N-methylpiperidine (NMP)), with β-diketiminato dimagnesium(I) reagents, [{( Ar Nacnac)Mg} 2 ] ( Ar Nacnac = [HC(MeCNAr) 2 ] À , Ar = mesityl (Mes) or 2,6-xylyl (Xyl)), have afforded deep red mixed valence aluminum hydride cluster compounds, [Al 6 H 8 (NR 3 ) 2 {Mg( Ar Nacnac)} 4 ], which have an average Al oxidation state of + 0.66, the lowest for any well-defined aluminum hydride compound. In the solidstate, the clusters are shown to have distorted octahedral Al 6 cores, having zero-valent Al axial sites and monovalent AlH 2 À equatorial units. Several novel by-products were isolated from the reactions that gave the clusters, including the MgÀ Al bonded magnesio-aluminate complexes, [( Ar Nacnac)(Me 3 N)MgÀ Al(μ-H) 3 [{Mg-( Ar Nacnac)} 2 (μ-H)]]. Computational analyses of one aluminum hydride cluster revealed its Al 6 core to be electronically delocalized, and to possess one unoccupied, and six occupied, skeletal molecular orbitals.