Sterically crowded aryloxide compounds of aluminium: hydrides and homoleptic aryloxides

Abstract

Interaction of [AlH₃(NMe₃)] and [AlH₂Cl(NMe₃)] with HOR¹(R¹= C₆H₂Bu^t₂-2,6-Me-4) allows for the isolation of [AlH₂(OR¹)(NMe₃)]1 and [AI(H)Cl(OR¹)(NMe₃)]2 respectively. Compound 1 exists in both mono- and di-meric forms in the solid state. The reaction of 1 with NH₂Bu^t results in ligand redistribution to give [AIH(OR¹)₂(NH₂Bu^t)]3. Similarly, multiple recrystallisation of 1 from Et₂O allows for the isolation of [AIH(OR¹)₂(OEt₂)]4, while addition of HOR²(R²= C₆H₃Ph₂-2,6) to 1 yields the mixed aryloxide complex [AIH(OR¹)(OR²)(NMe₃)]5. Interaction of compound 1 with benzophenone results in the formation of the bridged dimer [{AIH(OR¹)(µ-OCHPh₂)}₂]6. The reaction of 3 molar equivalents of HOR¹ with LiAlH₄ yields, in addition to [{Li(OR¹)(OEt₂)}₂], compound 4, which reacts futher with H₂O, HOR¹ or NH₂C₆H₂Cl₃-2,4,6 to give [{AI(µ-OH)(OR¹)₂}₂]7, [AI(OR¹)₃]8 or [AI(OR¹)₂(NHC₆H₂Cl₃-2,4,6)]13 respectively. Compounds 8 and 13 form stable Lewis acid–base complexes [Al(OR¹)₃L][L = MeCN 9, pyridine (py)10, OPPh₃11 or OC(C₅H₉)Bu^t-4 12] and [Al(OR¹)₂(NHC₆H₂Cl₃-2,4,6)L](L = Et₂O 14, py 15 or 3,5-dimethylpyridine 16). The presence of a slow ligand exchange for compound 9 and 12 was investigated by ¹H NMR spectroscopy. The molecular structures of 1, 3, 4, 8 and 12 have been confirmed by X-ray crystallography.