A computational study on the identity of the active catalyst structure for Ru(ii) carboxylate assisted C-H activation in acetonitrile

Density Functional Theory (DFT) calculations using a consistent methodology accounting for solvation, dispersion and thermal effects have been used to study C-H activation of the simple directing group substrate 2-phenylpyridine (a-H). The computational model uses acetate (-OAc) and benzene to represent the carboxylate and arene co-ligands coordinated at a Ru organometallic complex. A variety of different mechanisms ranging from cationic to neutral, ion-paired, arene free, two substrates bound, and solvent (MeCN) coordinated have been explored. Computed results indicate that the cationic pathways from "B+", [(C6H6)Ru(OAc)(a-H)](+), and "D+ (eta(6))", [(eta(6)-a-H)Ru(OAc)(a-H)](+), involve the lowest overall barriers to C-H activation. Consideration of solvent coordination leads to a complex variety of isomers and conformers. Here a neutral pathway with either one or two acetonitriles coordinated to the Ru centre give very low barriers to C-H activation.