Enhancement of C-H Oxidizing Ability in Co-O₂  Complexes through an Isolated Heterobimetallic Oxo Intermediate

The characterization of intermediates formed through the reaction of transition-metal complexes with dioxygen (O₂ ) is important for understanding oxidation in biological and synthetic processes. Here, the reaction of the diketiminate-supported cobalt(I) complex L^tBu Co with O₂ gives a rare example of a side-on dioxygen complex of cobalt. Structural, spectroscopic, and computational data are most consistent with its assignment as a cobalt(III)-peroxo complex. Treatment of L^tBu Co(O₂ ) with low-valent Fe and Co diketiminate complexes affords isolable oxo species with M₂ O₂ "diamond" cores, including the first example of a crystallographically characterized heterobimetallic bis(μ-oxo) complex of two transition metals. The bimetallic species are capable of cleaving C-H bonds in the supporting ligands, and kinetic studies show that the Fe/Co heterobimetallic species activates C-H bonds much more rapidly than the Co/Co homobimetallic analogue. Thus heterobimetallic oxo intermediates provide a promising route for enhancing the rates of oxidation reactions.