Rhodium-Catalyzed Sulfimidation Reactions: A Computational Study

The rhodium-catalyzed sulfimidation of thioethers using N-mesyloxycarbamates is a powerful tool to access chiral sulfilimines. 4-Dimethylaminopyridine (DMAP) and bis-(DMAP)­CH2Cl2 additives were found to be crucial to achieving high yields and selectivities. Experimental studies have suggested that the reaction mechanism would involve a rhodium/nitrenoid complex rather than a rhodium/nitrene species. A density functional theory (DFT) study to investigate rhodium-catalyzed sulfimidation reactions is reported herein. Both rhodium nitrene and rhodium nitrenoid species were proposed as key intermediates for the amination reaction. The role of additives was investigated, showing that the apical DMAP ligand was crucial to stabilize the rhodium nitrene intermediate. Furthermore, adding bis-(DMAP)­CH2Cl2 diverges the reaction mechanism from a rhodium nitrene insertion to a substitution-like reaction of the rhodium nitrenoid complex. This deviation was demonstrated to be substrate-dependent, which is in agreement with the experimental Hammett study.