Exploration\nof Organometallic Cobalt Intermediates\nin an Aminoquinoline-Directed Dehydrogenative Dimerization Reaction

This communication describes structure and reactivity\nstudies of\ncyclometalated cobalt complexes formed during the dehydrogenative\ndimerization of 2,3,4,5-tetrafluoro-<i>N</i>-(quinolin-8-yl)benzamide.\nThis substrate undergoes cyclometalation at Co(OAc)<sub>2</sub> to\nform an NNC cobalt(II) pincer complex. Single-electron oxidation with\nAgOAc results in a cobalt(III) intermediate that undergoes a second\ndirected C(sp<sup>2</sup>)–H activation to yield a bis-cyclometalated\noctahedral cobalt(III) product. This cobalt(III) species is inert\nto thermal carbon–carbon bond-forming reductive elimination\nupon heating at 160 °C for 48 h. However, treatment with ferrocenium\noxidants at room temperature results in oxidatively induced carbon–carbon\ncoupling via a putative cobalt(IV) intermediate.