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.