A Mechanistic Study of the Cobalt(I)-Catalyzed Amination of Aryl Halides: Effects of Metal and Ligand.

Abstract

Transition-metal-catalyzed amination of aryl halides is a useful approach for the synthesis of medicinal compounds, organic functional materials, and agrochemical compounds. A systematic DFT study has been performed to investigate the mechanism of the Co(I)-catalyzed amination of aryl halides by LiN(SiMe3)2 using (PPh3)3CoCl as the precatalyst. Our computational results suggest that the most favorable dissociative concerted C-I activation pathway in a triplet state consists of (a) dissociation of one PPh3 ligand, (b) concerted oxidative addition (OA) of the C-I bond, (c) transmetalation, (d) (optional) dissociation of the second PPh3 ligand, (e) C-N bond-forming reductive elimination (RE), and (f) ligand exchange to regenerate the active species. Comparatively, the associative concerted OA, radical, SH2/SN2, single electron transfer (SET), and σ-bond metathesis pathways should be less favorable due to their higher barriers or unfavorable reaction free energies. The effects of different metals (Rh and Ir) as centers in the catalyst were further examined and found to require higher reaction barriers, due to unfavorable dissociation of their stronger M-PPh3 bonds. These results highlight an advantage of the earth-abundant Co catalysts for the dissociative pathway(s). Overall, our study offers deeper mechanistic insights for the transition-metal-catalyzed amination and guides the design for efficient Co-based catalysts.