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 LtBuCo 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 LtBuCo(O2) with low‐valent Fe and Co diketiminate complexes affords isolable oxo species with M2O2 “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. Odd couple: Treatment of a side‐on dioxygen complex of cobalt with a low‐valent cobalt or iron diketiminate complex affords a homobimetallic Co/Co or a heterobimetallic Fe/Co oxo complex, respectively. C−H activation in the Co/Fe complex is three orders of magnitude faster than in the homobimetallic analogue.