Synthesis, characterization, cis-ligand substitution and catalytic alkane hydroxylation by mononuclear nickel(II) complexes stabilized with tetradentate tripodal ligands

• Synthesis and characterization of Ni(II) complexes containing N,N′-bis(8-quinolyl)ethane-1,2-diamine and N,N′-dimethyl-N,N′-bis(8-quinolyl)ethane-1,2-diamine is reported.
• Substitution of cis-ligands by 1,10-phenanthroline and 2,2′-bipyridine is achieved.
• Structures revealed importance of N–H⋯O and C–H⋯O interactions.
• Ni(II) compounds with cis-ligands afforded high yields of alcohol and ketone.

The synthesis and spectroscopic characterization of the mononuclear complexes [Ni(bqenH2)(H2O)2](ClO4)21 and [Ni(bqenMe2)(H2O)2](ClO4)22 (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)23, [Ni(bqenMe2)(phen)](ClO4)2 CH3CN 4, [Ni(bqenH2)(bpy)](ClO4)25, and [Ni(bqenMe2)(bpy)](ClO4)26. 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.

Synthesis, structural, spectroscopic, electrochemical properties and the catalytic hydroxylation of alkanes by six new nickel(II) complexes stabilized by non-heme tetradentate tripodal ligands namely N,N′-bis(8-quinolyl)ethane-1,2-diamine and N,N′-dimethyl-N,N’-bis(8-quinolyl)ethane-1,2-diamine is reported in this paper.Figure optionsDownload as PowerPoint slide