Facile O-atom insertion into C—C and C—H bonds by a trinuclear copper complex designed to harness a singlet oxene

摘要

Two trinuclear copper [Cu~ⅠCu~ⅠCu~Ⅰ(L)]~(1+) complexes have been prepared with the multidentate ligands (L) 3,3'-(1,4-diazepane-1,4-diyl)bis(1-((2-(dimethylamino)ethyl)(methyl)amino)propan-2-ol) (7-Me) and (3,3'-(1,4-diazepane-1,4-diyl)bis(1-((2-(diethylamino) ethyl)(ethyl) amino)propan-2-ol) (7-Et) as models for the active site of the particulate methane monooxygenase (pMMO). The ligands were designed to form the proper spatial and electronic geometry to harness a "singlet oxene," according to the mechanism previously suggested by our laboratory. Consistent with the design strategy, both [Cu~ⅠCu~ⅠCu~Ⅰ(L)]~(1+) reacted with dioxygen to form a putative bis(μ3-oxo)Cu~ⅡCu~ⅡCu~Ⅲ species, capable of facile O-atom insertion across the central C—C bond of benzil and 2,3-butane-dione at ambient temperature and pressure. These complexes also catalyze facile O-atom transfer to the C—H bond of CH_3CN to form glycolonitrile. These results, together with our recent biochemical studies on pMMO, provide support for our hypothesis that the hydroxylation site of pMMO contains a trinuclear copper cluster that mediates C—H bond activation by a singlet oxene mechanism.