Dual-site aqua mononuclear nickel(II) complexes of non-heme tetradentate ligands: Synthesis, characterization and reactivity

Abstract

Mononuclear compounds [Ni(BQCNMe2)(H2O)2](ClO4)2 1 and [Ni(BQCNH2)(H2O)2](ClO4)2 2 of N,N′-dimethyl-N,N′-di(quinolin-8-yl)cyclohexane-1,2-diamine (BQCNMe2) and N,N′-di(quinolin-8-yl)cyclohexane-1,2-diamine (BQCNH2) were synthesised and characterized by elemental analysis, IR/UV-Vis spectroscopy, cyclic voltammetry (CV)/differential pulse voltammetry (DPV) and X-ray powder pattern. [Ni(BQCNMe2)(en)](ClO4)2 3 and [Ni(BQCNMe2)(phen)](ClO4)2 4 were prepared by reacting 1 with ethylenediamine (en) and 1,10-phenanthroline (phen) respectively while [Ni(BQCNH2)(en)](ClO4)2 5 and [Ni(BQCNH2)(phen)](ClO4)2 6 were obtained from the reaction of 2. Compounds [Ni(BQENMe2)(en)](ClO4)2 7 and [Ni(BQENH2)(en)](ClO4)2.CH3CN 8 (BQENMe2 is N,N′-dimethyl-N,N′-bis(8-quinolyl)ethane-1,2-diamine) and BQENH2 is N,N′-bis(8-quinolyl)ethane-1,2-diamine) were synthesised similarly. Compounds 6 and 8 were characterized by single crystal X-ray diffractometry and their structural features are presented. The reactivity of 2 with H2O2/base was investigated. A new peak at 570 nm in the UV-Vis spectrum corresponding to 2a was obtained which on addition of 2-phenylpropionaldehyde (2-PPA) decays giving pseudo-first order rate constant of 9.2 × 10−3 s−1 and acetophenone as a major product. The catalytic hydroxylation of cumene and ethylbenzene by 1 and 2 in the presence of meta-chloroperbenzoic acid (m-CPBA) was investigated.