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, CF2 , and SiH2 ) 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.