Revisiting the Mechanism of Asymmetric Ni-Catalyzed Reductive Carbo-Carboxylation with CO 2 : The Additives Affect the Product Selectivity.

The mechanistic details of the asymmetric Ni-catalyzed reductive cyclization/carboxylation of alkenes with CO 2 have been revisited using DFT methods. Emphasis was put on the enantioselectivity and the mechanistic role of Lewis acid additives and in situ formed salts. Our results show that oxidative addition of the substrate is rate-limiting, with the formed Ni(II)-aryl intermediate preferring a triplet spin state. After reduction to Ni(I), enantioselective cyclization of the substrate occurs, followed by inner sphere carboxylation. Our proposed mechanism reproduces the experimentally observed enantiomeric excess and identifies critical C-H/O and C-H/N interactions that affect the selectivity. Further, our results highlight the beneficial effect of Lewis acids on CO 2 insertion and suggest that in situ formed salts influence if the 5-exo or 6-endo product will be formed.