Synthesis, characterization, cis-Ligand substitution and catalytic alkane hydroxylation by mononuclear Nickel(II) complexes stabilized with tetradentate ripodal ligands

Abstract

The synthesis and spectroscopic characterization of the mononuclear complexes [Ni(bqenH2)(H2O)2](ClO4)2 1 and [Ni(bqenMe2)(H2O)2](ClO4)2 2 (where bqenH2 = N,N?-bis(8-quinolyl)ethane-1,2-diamine and bqenMe2 = N,N'-dimethyl-N,N'-bis(8-quinolyl)ethane-1,2-diamine) is reported. The bqenMe2 ligand was prepared by a simple modification to the earlier procedure. The reaction of 1 and 2 with 1,10-phenanthroline (phen) or 2,2'-bipyridine (bpy) resulted in the formation of [Ni(bqenH2)(phen)](ClO4)2 3, [Ni(bqenMe2)(phen)](ClO4)2 CH3CN 4, [Ni(bqenH2)(bpy)](ClO4)2 5, and [Ni(bqenMe2)(bpy)](ClO4)2 6. The redox properties of 1-6 are reported. The crystal structures of 3 and 4 consist of distorted octahedral [Ni(bqenH2)(phen)]2+ and [Ni(bqenMe2)(phen)]2+ cations which are stabilized by N-H...O and C-H-O interactions. Compounds 1 and 2 afforded hydroxylation of alkanes with high alcohol to ketone ratio in the presence of m-CPBA oxidant.