New Mn(II), Co(II), Ni(II) and Cu(II) complexes of a tetradentate Schiff base ligand [bis(2-hydroxyanil)acetylacetone], "2-[{1-methyl-3-[(2-hydroxyphenyl)imino]butylidene}amino]phenol", H(2)haacac, have been prepared and characterized by elemental analyses, IR and conductometry. The results suggest that the Schiff base is a bivalent anion with tetradentate ONNO donors derived from the phenolic oxygen and azomethine nitrogen. The formulae was found to be [M(haacac)] for the 1: 1 non-electrolytic complexes. Alumina-supported [M(haacac)] complexes catalyze the oxidation of cyclohexene with tert-butylhydroperoxide (TBHP). The major products of the reaction were 2-cyclohexene-1-ol(-OH), 2-cyclohexene-1-one (C=O) and 2-cyclohexene-1-(tert-butylperoxy) (-(OOBu)-Bu-t). The influence of temperature, solvent and time for the oxidation reaction has been studied. The selectivity of 2-cyclohexene-1-(tert-butylperoxy) varied with reaction temperature. Mn(haacac)-alumina shows significantly higher catalytic activity than other alumina-supported complexes. (C) 2003 Elsevier Science B.V. All rights reserved.