Exploration of Organometallic Cobalt Intermediates in an Aminoquinoline-Directed Dehydrogenative Dimerization Reaction

This communication describes structure and reactivity studies of cyclometalated cobalt complexes formed during the dehydrogenative dimerization of 2,3,4,5-tetrafluoro-N-(quinolin-8-yl)benzamide. This substrate undergoes cyclometalation at Co(OAc)2 to form an NNC cobalt(II) pincer complex. Single-electron oxidation with AgOAc results in a cobalt(III) intermediate that undergoes a second directed C(sp2)–H activation to yield a bis-cyclometalated octahedral cobalt(III) product. This cobalt(III) species is inert to thermal carbon–carbon bond-forming reductive elimination upon heating at 160 °C for 48 h. However, treatment with ferrocenium oxidants at room temperature results in oxidatively induced carbon–carbon coupling via a putative cobalt(IV) intermediate.