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

摘要

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 _2C _6Cl _4)(py) (6). Similar results were obtained when 1a was reacted with 9,10-phenanthrenequinone to afford [ONO]Al(o-O _2C _(14)H _8)(py) (7) or with pyrene-4,5-dione to afford [ONO]Al(o-O _2C _(16)H _8)(py) (8). Structural, spectroscopic and preliminary magnetic measurements on 6-8 suggest ligand non-innocent redox behavior in these complexes.