Plural bonding interactions in Al(μ2-H)2TM species

Abstract

The reaction of aluminum hydride [(Ar^BIG-bian)AlH₂]⁻[Li(THF)₄]⁺ (1) (Ar^BIG-bian = dianion of 1,2-bis[(2,6-dibenzhydryl-4-methylphenyl)imino]acenaphthene) with TM(CO)₆ yields σ-complexes [(Ar^BIG-bian)Al(μ²-H)₂TM(CO)₄]⁻[Li(Solv)₃]⁺ (TM = Cr, 2; Mo, 3; W, 4), in which two hydride ligands symmetrically bridge the Al and TM centers. Molybdenum hydride [(Ar^BIG-bian)Al(μ²-H)₂Mo(CO)₄Li(THF)₃] 3b reacts with ammonia through H₂ elimination to form an amido-bridged derivative [(Ar^BIG-bian)Al(μ²-NH₂)₂Mo(CO)₄]⁻[Li(THF)₄]⁺ (5). In contrast, the reactions of hydride 1 with Cp₂Ni and Cp₃Er (Cp = C₅H₅) afford a unique Ni(II)(μ²-H)₂Al(III) complex [(Ar^BIG-bian)(THF)Al(μ²-H)₂NiCp] (6) and dihydride [(Ar^BIG-bian)Al(μ²-H)₂Er(Cp)₂THF] (7), respectively. The latter represents the first crystallographically characterized Er/Al complex. Products 2–7 have been identified via IR and NMR spectroscopy, and their molecular structures were determined via single-crystal X-ray analysis. The electronic structures of 2, 3 and 6 were examined via DFT calculations, which revealed direct Al–TM bonding.