Theoretical Investigation of Regioselectivity in the Rh‐Catalyzed Coupling Reaction of 3‐Phenylthiophene with Styrene

Abstract

The regioselectivity of the Rh‐catalyzed coupling reaction of 3‐phenylthiophene with styrene was investigated by quantum chemistry calculations. Previous experimental studies showed that styrene selectively couples to the phenyl moiety of the phenylthiophene in the coupling reaction. In this work, possible reaction paths for the coupling were evaluated using theoretical calculations, and the most energetically reasonable catalytic sequence was found to be the following: (1) The Rh catalyst cleaves two C–H bonds on the phenyl and thiophene moieties, leading to a five‐membered rhodacycle intermediate. (2) Styrene is inserted into the C–Rh bond on the phenyl group of the rhodacycle. (3) Then, β‐hydrogen elimination occurs to form 2′‐alkenylated 3‐phenylthiophene. Natural bond orbital analysis results suggest that the key product‐determining step, i.e., the preferential insertion of styrene to the phenyl side (2), occurs due to the difference in π‐electron density between the phenyl and thienyl groups of the five‐membered rhodacycle intermediate.