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Ni-catalyzed carboxylation of the C(sp(3))-Cl bond with CO2 in the presence of MgCl2 was theoretically investigated. MgCl2 plays three crucial roles in stabilization of a Ni(I)-CO2 adduct and acceleration of the CO2 insertion as a non-innocent additive and the one-electron reduction process as one kind of reagent.

In Ni(0)-catalyzed carboxylation reaction of aryl chloride with CO2, the formation of a Ni(I) species is crucial, because the CO2 insertion into the Ni(I)-Ph bond easily occurs but that into the Ni(II)-Ph bond cannot. This is a key point of this successful carboxylation reaction.

Several ortho, meta, and para substituted benzoic acids have been studied to quantify the substituent effects by analysing subtle variations in the molecular electrostatic potential minimum (Vmin) at the response site of the carboxylic acid moiety using density functional theory. For the first time, the ortho substituent effect is separated into contributions from electronic and proximity effects. A molecular fragment approach in conjunction with a rotation experiment on the COOH moiety of benzoic acid was used to quantify the proximity effects. The quantified proximity effect is in accord with previously proposed steric parameters. The proximity effect-corrected Vmin of ortho systems showed excellent linear correlations to both Vmin of para and meta systems which enabled the computation of the meta : para, ortho : para and meta : ortho electronic effect ratios yielding respective values of 1 : 1.108, 1 : 1.042 and 1 : 1.047. The additive nature of the substituent effects was also tested using the Vmin computation on multiply-substituted benzoic acids. It is found that the total substituent effect is approximately 86.3% of the sum of the individual contributions which was in contrast to a value of 98.5% observed in aliphatic systems (Phys. Chem. Chem. Phys., 2008, 10, 6492–6499).