C_sp2–H Amination Reactions Mediated by Metastable Pseudo-O_hMasked Aryl-Co^III-nitrene Species

Abstract

Cobalt-catalyzed C–H amination via M-nitrenoid species is spiking the interest of the research community. Understanding this process at a molecular level is a challenging task, and here we report a well-defined macrocyclic system featuring a pseudo- O h aryl-Co III species that reacts with aliphatic azides to effect intramolecular C sp2 –N bond formation. Strikingly, a putative aryl-Co=NR nitrenoid intermediate species is formed and is rapidly trapped by a carboxylate ligand to form a carboxylate masked-nitrene, which functions as a shortcut to stabilize and guide the reaction to productive intramolecular C sp2 –N bond formation. On one hand, several intermediate species featuring the C sp2 –N bond formed have been isolated and structurally characterized, and the essential role of the carboxylate ligand has been proven. Complementarily, a thorough density functional theory study of the C sp2 –N bond formation mechanism explains at the molecular level the key role of the carboxylate-masked nitrene species, which is essential to tame the metastability of the putative aryl-Co III =NR nitrene species to effectively yield the C sp2 –N products. The solid molecular mechanistic scheme determined for the C sp2 –N bond forming reaction is fully supported by both experimental and computation complementary studies.

Co(III) Intermediates in Cobalt-Catalyzed, Bidentate Chelation Assisted C(sp2)-H Functionalizations

“…Similar to a previous report [31], isolated cobalt intermediates 28a and 30 were used as cat-alysts, providing the desired product 29 with yields 67-87%, indicating that organometallic complexes 28a and 30 are catalytically active species. Ribas and co-workers are continuing the investigation of Co(III)-aryl complex 28 reactivity towards other transformations [33].…”

Square-planar imido complexes of cobalt: synthesis, reactivity and computational study

“…13 Cobalt, in particular, has proven promising as a focal point for further catalyst design with several systems displaying both efficiency and selectivity for C-H amination. [14][15][16][17][18][19] In this vein, recent work with a cobalt PNP pincer system by Chirik and coworkers disclosed one of the first examples of an isolable imido complex possessing a square-planar geometry (Scheme 1). 20 The compound was prepared by treatment of a cobalt(I) dinitrogen complex with mesityl azide.…”