A Tricopper(I) Complex Competent for O Atom Transfer, C-H Bond Activation, and Multiple O2 Activation Steps

Oxygenation of a tricopper(I) cyclophanate (1) affords reactive transients competent for C-H bond activation and O atom transfer to various substrates (including toluene, dihydroanthracene, and ethylmethylsulfide) based on H-1 NMR, gas chromatography/mass spectrometry (MS), and electrospray ionization (ESI)/MS data. Low product yields (<1%) are determined for C-H activation substrates (e.g, toluene, ethylbenzene), which we attribute to competitive ligand oxidation. The combined stopped-flow UV/visible, electron paramagnetic resonance, ESI/MS, H-1 NMR, and density functional theory (DFT) results for reaction of 1 with O-2 are consistent with transient peroxo- and di(oxo)-bridged intermediates. DFT calculations elucidate a concerted proton-coupled electron transfer from toluene to the di(mu-oxo) intermediate and subsequent radical rebound as the C-H activation mechanism. Our results support a multicopper oxidase-like mechanism for O-2 activation by 1, traversing species similar to the coplanar Cu3O2 unit in the peroxy and native intermediates.