Ancillary ligand effects and microwave-assisted enhancement on the catalytic performance of cationic ruthenium(II)-CNC pincer complexes for acceptorless alcohol dehydrogenation

Abstract

The application of cationic Ru(II)-CNC pincer complexes [Ru(CNC)(CO)(PPh3)Cl]PF6 (1), [Ru(CNC)(PPh3)2Cl]PF6 (2), [Ru(CNC)(η2:η2-COD)Cl]PF6 (4), and [Ru(CNC)(DMSO)2Cl]PF6 (5) in acceptorless dehydrogenation of alcohols is reported under conventional “oil-bath” and microwave heating conditions. The effect of different ancillary ligands (CO, PPh3, COD, and DMSO) have been demonstrated during catalysis. Complexes with more π-acid ligands CO and COD perform better compared with those with PPh3 and DMSO ligands. A plausible mechanism is proposed based on NMR and mass investigation during the catalysis. The catalytic performance matches with the order of trans effect among the four ancillary ligands studied in these complexes. Further, a significant reduction in reaction time, as well as reaction temperature, was observed for catalytic reactions under the microwave-assisted reaction compared with the oil-bath heating reaction. © 2022 John Wiley & Sons Ltd.