A DFT study on the mechanism of Wolff Rearrangement in a fivemember Iridacycle

The reaction mechanism of the Wolff-like ring contraction in a five-membered iridacycle (A, diazoalkane compound) at room temperature was studied by density functional theory (DFT). The calculation indicates an exothermic reaction favored by −31.5 kcal/mol with a barrier of 26.4 kcal/mol in free energy and a concerted mechanism, in which the extrusion of N2 and the 1,3-shift rearrangement in the diazo complex (A) occurs simultaneously. The facilitation of Ir(III) lowers the barrier for the rearrange undergoing at room temperature without the need of the activation by heat or light in the conventional organic version. Furthermore, the frontier molecular oribital analysis shows that LUMO+3, which is largely localized on the central metal and the coordinating CO, in A is able to strongly interact with the “carbenoid” carbon atom when N2 is released. The corresponding addition of the carbenoid carbon to this carbonyl is located as an alternative reaction path. The calculated barrier is 5.5 kcal/mol higher in free energy than that for the major product as found in the experiment. This study not only points out the orbital interactions in the active intermeidate but also provides an alternative reaction path to develop further applications for this iridium complex