%0 Journal Article
%T Mechanism of the Catalytic Carboxylation of Alkylboronates with CO2 Using Ni-NHC Complexes: A DFT Study.
%A Delarmelina M
%A Marelli E
%A de M Carneiro JW
%A Nolan SP
%A Bühl M
%J Chemistry
%V 23
%N 59
%D Oct 2017 20
%M 28856746
%F 5.02
%R 10.1002/chem.201703567
%X A new mechanism is proposed for the Ni-catalyzed carboxylation of organoboronates with CO2 . DFT investigations at the PBE0-D3 level have shown that direct CO2 addition to the catalysts [Ni(NHC)(Allyl)Cl] (1NHC , NHC=IMe, IPr, SIPr and IPr*) is kinetically disfavored and formation of the Aresta-type intermediate is unlikely to occur. According to the mechanism proposed here, the carboxylation process starts with addition of the borate species to 1NHC , followed by transmetalation, CO2 cycloaddition and carboxylation. The rate-determining step was identified as being the transmetalation process, with computed relative free energy barriers of 34.8, 36.8, and 33.5 kcal mol-1 for 1IPr , 1SIPr and 1IPr* , respectively.