Investigations into the ligand steric and electronic effects of Ru-catalyzed C–H bond arylation directed by 8-aminoquinoline as a bidentate-directing group

Abstract

In this study, we report an investigation into the steric (cone angle, θ) and electronic properties of ligands in Ru-catalyzed C–H arylation of aromatic benzamides bearing 8-aminoquinoline as an N,N’-bidentate-directing group. The study employs [RuCl2( p-cymene)]2 as a precatalyst, and a ligand, under study, as a cocatalyst. Various electronically and sterically different monodentate and bidentate phosphine ligands were examined. Other ligands such as phosphites and amines were also tested. The study reveals that while bidentate phosphines, phosphites, and aryl and alkyl amines were found to be ineffective, monodentate triarylphosphines represented by triphenylphosphine were found to be the most effective ligands in the Ru-catalyzed C–H arylation under the conditions specified. In addition, the study reveals that there is a correlation between the steric effects, cone angle (θ) and the reaction efficiency. Thus, for symmetrical phosphine ligands, as the cone angle increases, the yield of the CH arylation product gradually decreased. Moreover, the electronic properties of triarylphosphine ligands influenced the reaction as demonstrated by the decreased ability of electron-poor ligands to promote the reaction. The study also reveals a correlation between the electronic parameter, υCO, of the triarylphosphine ligand and the reaction efficiency. As the carbonyl stretching frequency increases, the reaction yield gradually decreased.