Mechanistic understanding of the acceptorless dehydrogenation reaction catalyzed by low valent Co(I) complex

Coordination complexes based on the first-row transition metal play pivotal role in homogenous catalysis. However, the variable oxidation states and complicated electronic configurations of first-row transition metal centers result in the ambiguous mechanism. Herein, focusing on a typical Co(I)-PNP pincer catalyst developed by Madsen et al. (Chemcatchem, 11 (2019) 2707-2712.), the diversity of mechanistic scenarios caused by low valent cobalt complex is displayed and the competition of each plausible reaction pathways were investigated based on density functional theory (DFT) calculation. The calculated results suggest that the MLC mechanism mediated by Co(I) center prevails in different stage among all possible reaction pathways. Further analysis using the activation strain model elucidates the dual active sites in MLC mechanism leads to a higher interaction energy compared with the Co(I/III) mechanism, in which the reaction basically occurs on the metal center. However, in the high spin state, the metal and the ligand cooperate to provide more interaction energy in the activation of chemical bonds, thereby reducing the activation energy barrier. These theoretical findings are anticipated to enhance current understanding of homogeneous catalysis based on 3d low valent metal centers.