Aluminum complexes of the redox-active [ONO] pincer ligand

A series of aluminum complexes containing the tridentate, redox-active ligand bis(3,5-di-tert-butyl-2-phenol)amine (ONO]H(3)) in three different oxidation states were synthesized. The aluminum halide salts AlCl(3) and AlBr(3) were reacted with the doubly deprotonated form of the ligand to afford five-coordinate ONHO(cat)]AlX(solv) complexes (1a, X = Cl, solv = OEt(2); 1b, X = Br, solv = THF), each having a trigonal bipyramidal coordination geometry at the aluminum and containing the ONHO(cat)](2-) ligand with a protonated, sp(3)-hybridized nitrogen donor. The ONO] ligand platform may also be added to aluminum through the use of the oxidized ligand salt ONO(q)]K, which was reacted with AlCl(3) in the presence of either diphenylacetylacetonate (acacPh(2)(-)) or 8-oxyquinoline (quinO(-)) to afford ONO(q)]Al(acacPh(2))Cl (2) or ONO(q)]Al(quinO)Cl (3), respectively, with well-defined ONO(q)](-) ligands. Quinonate complexes 2 and 3 were reduced by one electron to afford the corresponding complexes K{ONO(sq)]Al(acacPh(2))(py)} (4) and K{ONO(sq)]Al(quinO)(py)} (5), respectively, containing well-defined ONO(sq)](2-) ligands. The addition of tetrachloro-1,2-quinone to 1a in the presence of pyridine resulted in the expulsion of HCl and the formation of an aluminum complex with two different redox active ligands, ONO]Al(o-O(2)C(6)Cl(4))(py) (6). Similar results were obtained when 1a was reacted with 9,10-phenanthrenequinone to afford ONO]Al(o-O(2)C(14)H(8))(py) (7) or with pyrene-4,5-dione to afford ONO]Al(o-O(2)C(16)H(8))(py) (8). Structural, spectroscopic and preliminary magnetic measurements on 6-8 suggest ligand non-innocent redox behavior in these complexes.