Facile C−H Bond Cleavage via a Proton-Coupled Electron Transfer Involving a C−H···CuII Interaction

• Published in: Journal of the American Chemical Society 2010-09, Vol.132 (35), p.12299-12306
• Main Authors: Ribas, Xavi, Calle, Carlos, Poater, Albert, Casitas, Alicia, Gómez, Laura, Xifra, Raül, Parella, Teodor, Benet-Buchholz, Jordi, Schweiger, Arthur, Mitrikas, George, Solà, Miquel, Llobet, Antoni, Stack, T. Daniel P
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja101599e

The present study provides mechanistic details of a mild aromatic C−H activation effected by a copper(II) center ligated in a triazamacrocylic ligand, affording equimolar amounts of a CuIII-aryl species and CuI species as reaction products. At low temperatures the CuII complex 1 forms a three-center, three-electron C−H···CuII interaction, identified by pulse electron paramagnetic resonance spectroscopy and supported by density functional theory calculations. C−H bond cleavage is coupled with copper oxidation, as a CuIII-aryl product 2 is formed. This reaction proceeds to completion at 273 K within minutes through either a copper disproportionation reaction or, alternatively, even faster with 1 equiv of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), quantitatively yielding 2. Kinetic studies of both reactions strongly implicate a rate-limiting proton-coupled electron transfer as the key C−H activation step, a mechanism that does not conform to the C−H activation mechanism in a NiII analogue or to any previously proposed C−H activation mechanisms.