Metal complexes of a chiral quadridentate Schiff base

Abstract

Chiral metal Schiff-base complexes [AlL(Et)], [TiLCl₂], [VO(L)], [(FeL)₂O], [CoL], [NiL], [CuL], [ZrLCl₂], [RuL(CO)₂] and trans-[RuL(NO)Cl]([H₂L =(R,R)-(–)-N,N′-bis(3,5-di-tert-butylsalicylidene)cyclohexane-1,2-diamine] were synthesized and characterized. The structures of [CoL] and trans-[RuL(NO)Cl] have been established by X-ray crystallography. The former has a pseudo-square-planar geometry with Co–N and Co–O distances of 1.88 and 1.84 Å, respectively. The geometry around Ru in trans-[RuL(NO)Cl] is octahedral with Ru–N (nitrosyl) and Ru–Cl distances of 1.72(2) and 2.354(4)Å, respectively, and Ru–N–O 175(2)°. The cyclic voltammograms for the metal Schiff-base complexes show reversible M^III–M^II and ligand-centred oxidation couples. Treatment of NiL with AgBF₄ afforded air-stable [NiL]BF₄, which is formulated as a nickel(II) complex of the Schiff-base cation radical.