Cycloaddition reactions of metalloaromatic complexes of iridium and rhodium: a mechanistic DFT investigation

The mechanistic details of 1,2- and 1,4-cycloaddition reactions of acetone, CO(2), and CS(2) to isostructural iridiabenzene, iridiapyrylium, and iridiathiabenzene complexes, as well as their rhodium analogues, were elucidated by density functional theory (DFT) at the PCM/mPW1K/SDB-cc-pVDZ//mPW1K/SDD level of theory. The calculated reaction profiles concur with reported experimental observations. It was found that the first complex reacts via a concerted reaction mechanism, while the latter two react by a stepwise mechanism. Several factors affecting the reaction mechanisms and outcome were identified. They include the composition and size of the metal-aromatic ring, the length of the substrate C=X (X = O, S) bond, the geometry of the product, the symmetry of the frontier molecular orbitals, and the type of reaction mechanism involved.