A theoretical research on the regioselectivity for ortho C−H activation of aromatic ketone in Murai reaction

Abstract

RuH2(CO)(PPh3) is an important catalyst for Murai reaction, which brings a very high regioselectivity in ortho C-H activation of aromatic ketone. In this work, we studied the mechanism of ruthenium complexes catalyzed aromatic ketone ortho C-H activation reaction by density functional method (DFT) method, and explained the regioselectivity by designing three different reaction processes, path a, path b and path c. Calculated results show that the barrier for C–H activation is 1.1 kcal/mol, which explains well the regioselectivity. In the comparison of path a and path b, it is found that the C=C double bond is easier to insert to the Ru–H bond than the Ru–C bond. In addition, the process of C–C bond formation (C–C activation) is the rate determining step in the reaction cycle no matter it appears in the olefin insertion step in path a or in the reductive elimination step in path b. The comparison of the path c with path a and path b suggests that the steric hindrance in the formation of C–C bond in path c is much bigger than that in path a and path b, which results in a higher energy barrier in this step.