Mechanism of the rhodium(III)-catalyzed alkenylation reaction of N-phenoxyacetamide with styrene or N-tosylhydrazone: a computational study

A systematic density functional theory study has been conducted to examine the mechanisms involved in the rhodium(III)-catalyzed alkenylation of N-phenoxyacetamide with two different substrates (i.e., styrene and N-tosylhydrazone). The density functional theory calculations indicated that the reaction of the N-tosylhydrazone substrate resulted in the formation of a Rh(V)–nitrene intermediate via the cleavage of the O–N bond of N-phenoxyacetamide, whereas the styrene substrate resulted in an Rh(I) species through consecutive β-H elimination and H migration steps to the internal oxidant. The differences observed between the N-tosylhydrazone and styrene systems were attributed to differences in the reactivity of their Rh(V)–nitrene intermediates. For example, the N-tosylhydrazone formed a five-membered Rh(V)–nitrene intermediate, which was readily reduced to a Rh(III) species by tautomerization, whereas this pathway was energetically unfavorable for the styrene substrate.