Palladium-catalysed processes for the formation of carbon-carbon bonds, i.e., coupling reactions of organic halides (R(1)X) and main-group organometallic compounds (R(2)M) are most frequently applied in synthesizing biologically and pharmaceutically important organic molecules. In this article, we provide a critical review on theoretical studies of the palladium-catalysed carbon-carbon cross-coupling reactions, and give an up-to-date summary of the current understanding of the cross-coupling reactions from a theoretical point of view (108 references).

Silver- and copper-catalyzed decarboxylation reactions of aryl carboxylic acids were investigated with the aid of density functional theory calculations. The reaction mechanism starts with a carboxylate complex of silver or copper. Decarboxylation occurs via ejecting CO(2) from the carboxylate complex followed by protodemetallation with an aryl carboxylic acid molecule to regenerate the starting complex. Our results indicated that the primary factor to affect the overall reaction barriers is the ortho steric destabilization effect on the starting carboxylate complexes for most cases. Certain ortho substituents that are capable of coordinating with the catalyst metal center without causing significant ring strain stabilize the decarboxylation transition states and reduce the overall reaction barriers. However, the coordination effect is found to be the secondary factor when compared with the ortho effect.

Decarboxylation process in a series of PdL(2)X(η(2)-OOCAr(R)) complexes 2OS(R) (L = DMSO; X = OOCCF(3)(-); R = H, OMe, NO(2), Me and CN) with substituent R at an ortho, meta or para position were investigated with the aid of density functional theory calculations. Through our study, we found that the OOCCF(3)(-) ligand is not just a spectator ligand but assists the decarboxylation process. The results indicated that electron-donating substituents have greater promotion effect than electron-withdrawing substituents on the decarboxylation process. An ortho substituent in the substrate ligands OOCAr(R)(-) is normally necessary for a successful decarboxylation. The reason behind this has been explained.