DFT study on ruthenium-catalyzed N-methylbenzamide-directed 1,4-addition of the ortho C–H bond to maleimide via C–H/C–C activation

Abstract

Density functional theory has been used to investigate ruthenium-catalyzed N-methylbenzamide directed 1,4-addition of the ortho C–H bond to maleimide via C–H/C–C activation, in which the active catalyst was proved to be ionic Ru(OAc)(SbF₆)(p-pymene) and not neutral Ru(OAc)₂(p-pymene). The plausible catalytic cycles involve C–H activation, maleimide insertion and protonation, and the recovery of the catalyst and the formation of the final product. The calculations confirmed that the fragment of SbF₆ could leave the ligand field of the Ru center to form N–H⋯F hydrogen bonding when the O atom in the carbonyl group of the first reactant 1a approaches the Ru center, and it could return to the Ru coordination center in the last step to complete the recovery of the catalyst and the formation of the final product. It was deduced from the energy span model that the TOF-determining transition state (TDTS) and intermediate (TDI) are TS4 and INT1, and thus the activation free-energy barrier is 28.2 kcal mol⁻¹ at a temperature of 373 K. The effects of the solvent, the directing group and catalyst type have been addressed in this paper.