Aluminum-a-diimine ligand complexes have been prepared for several diimine ligands. The singly reduced complex (LDipp-)AlCl2 (LDiip = N,N'-bis[2,6-diisopropylphenyl]-2,3-dimethyl-1,4-diazabutadiene) and the doubly reduced complex (LMes2-)AlCl(THF) (LMes = N,N'-bis[2,4,6-trimethylphenyl]-2,3-dimethyl-1,4-diazabutadiene), were prepared by direct reduction of the ligands with sodium metal followed by salt metathesis with AlCl3 in 77% and 81% yields, respectively. The (LMes�)AlCl2 complex was prepared through one-electron oxidative functionalization of (LMes2-)AlCl(THF) with either AgCl (89%) or CuCl (65%). Al-a-diimine complexes with neutral ligands were prepared for a-diimines lacking ortho substitution: reaction of either N,N'-diphenyl-2,3-dimethyl-1,4-diazabutadiene (LPh) or N,N'-di[4-methylphenyl]-2,3-dimethyl-1,4-diazabutadiene (LTol) gave the fully neutral ligand compounds ([(diimine)2AlCl2][AlCl4]) in 88% and 49% yield, respectively. Complexes were characterized by 1H NMR spectroscopy, X-ray diffraction, and DFT. Cyclic voltamograms of the compounds revealed multiple redox processes. Aluminium complexes of nitroxide ligands have also been prepared. Reaction of two equivalents of a N-tert-butyl-N-(2-R-pyridyl)hydroxylamine(2-(tBuNOH)py-R) with AlMe2Cl gives the corresponding [2-(tBuNO)py-R]2AlCl complexes in good yield. Complexes where R = H, 4-CH3, and 4-CF3 were all prepared and characterized using 1H and 13C NMR spectroscopies and X-ray diffraction. Redox features of the ligand are retained in the aluminium complexes.

Synthesis and characterization of aluminum complexes of redox-active ligands

248th National Meeting (2014)

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