Ligand-Mediated Regioselective Rhodium Catalyzed Benzotriazole-Allene Coupling: Mechanistic Exploration and Quantum Chemical Analysis.

The ligand-controlled rhodium catalyzed regioselective coupling of 1,2,3-benzotriazoles and allenes was investigated by density functional theory calculations. As allylation can occur at either the N1 or N2 position of the 1,2,3-benzotriazole, the complete Gibbs free energy profiles for both pathways were computed. A kinetic preference emerged for the experimentally observed N1 allylation with the JoSPOphos ligand, while N2 allylation was favoured with DPEphos. Analysis of the regiodetermining oxidative addition step using the activation strain model in conjunction with a matching energy decomposition analysis has revealed that the unprecedented N2 reaction regioselectivity is dictated by the strength of the electrostatic interactions between the 1,2,3-benzotriazole and the rhodium catalyst. The nature of the electrostatic interaction was rationalized by analysis of the electrostatic potential maps and Hirshfeld charges: a stabilizing electrostatic interaction was found between the key atoms involved in the oxidative addition for the N2 pathway, analogous interactions are weaker in the N1 case.