Reaction Mechanisms on Unusual 1,2‐Migrations of N‐Heterocyclic Carbene‐Ligated Transition Metal Complexes

Unusual 1,2‐migration reactions of N‐heterocyclic carbene (NHC) on transition metals were investigated using density functional theory calculations. Our results reveal that the electronic properties, ring strain of the four‐membered ring, and aromaticity of NHC play crucial roles in the thermodynamics of such a 1,2‐migration. Further studies show that changing the methylene on the metal center in the reactant with a more electronegative group (NH or O) will lead to the formation of products with nitrogen coordinating to the metal center, whereas other groups (BH, CF 2 , and SiH 2 ) will make such a 1,2‐migration reverse. In addition, the reversed rearrangement of 1,2‐boron, silyl migration could be thermodynamically and kinetically favorable.