Copper Complexes Containing o-Phenylenediamine-Based Pentadentate Ligands Catalyze TEMPO-Mediated Alcohol Oxidation

Yuji Mikata^1*Miyu Akedo¹Yutaka Ohsedo¹Sunao Shoji¹Attawit Jehdaramarn²Preeyanuch Sangtrirutnugul^2*Yasuhiro Funahashi³

• ¹Nara Women's University, Nara, Japan
• ²Mahidol University - Phayathai Campus, Bangkok, Thailand
• ³Osaka Daigaku, Suita, Japan

A set of o-phenylenediamine-based pentadentate ligands having pyridine and quinoline binding sites has been prepared. The weak metal binding ability of anilinic nitrogen atoms and rigid chelate structure of o-phenylenediamine skeleton serve as unique metal coordination properties of the present ligand library. Not only the variation in pyridine and quinoline binding sites, but also non-coordinating alkyl groups (CH3 or CH2Ph) in the ligand structure makes significant differences in the coordination structure of copper(II) complexes. In the aerobic alcohol oxidation reaction in the presence of CuBr and TEMPO, the less electron-donating ligand, Bn-TQPHEN (N-benzyl-N,N',N'-tris(2-quinolylmethyl)-1,2-phenylenediamine, L4), exhibited higher activity in comparison to Me-TPPHEN (N-methyl-N,N',N'-tris(2-pyridylmethyl)-1,2-phenylenediamine, L1). The present study proposes future direction of pentadentate ligands and relevance to the redox-active copper metalloenzymes.