Anion mediated formation of different Schiff bases from the same precursors and their nickel(II) complexes with different nuclearity

Abstract

Two nickel(II) complexes, [Ni2 (H2O)4](NO3)2 (1) and [Ni5 (OAc)6(OH)2] · 5.5H2O (2), have been synthesized and structurally characterized by X-ray crystallographic study, where L1 and L2 represent 2-formyl-4-methyl-6-(1-(2-aminomethyl)piperidine)-iminomethylphenolate and 4-methyl-2,6-bis(1-(2-aminomethyl)piperidine)-iminomethylphenolate, respectively. One-pot reactions between 2,6-diformyl-4-methylphenol with 1-(2-aminoethyl)piperidine, in the presence of nickel(II) nitrate and nickel(II) acetate, afforded in situ [1 + 1] and [1 + 2] condensation leading to Schiff-bases HL1 and HL2, and to 1 and 2 of different nuclearity. Both processes were conducted under the same reaction conditions in anhydrous EtOH. Preferential attainment of bi- or pentanuclear compounds is mediated by the anion of the Ni(II) salt. Complex 1 is formed by two unsymmetrical tridentate L1 chelating in a head-tail fashion to make a centrosymmetric phenoxido-bridged Ni(II) dimer. Two waters complete octahedral coordination. Conversely in 2, two [Ni2(OAc)L2]+ units, having a syn-syn bidentate bridging acetate, embrace a third Ni through bridging acetate and μ3-hydroxide, giving rise to an adduct of C2 symmetry where the compartmental ligand planes form a dihedral angle of ca. 82°. The catecholase activity of these complexes were explored and both complexes effectively catalyze the conversion of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylbenzoquinone (3,5-DTBQ).