Novel ruthenium complexes bearing bipyridine-based and N-heterocyclic carbene-supported pyridine (NCN) ligands: the influence of ligands on catalytic transfer hydrogenation of ketones

Piyasaengthong, Akkharadet; Williams, Luke J.; Yufit, Dmitry S.; Walton, James W.

Abstract

Transfer hydrogenation (TH) is a powerful synthetic tool in the production of secondary alcohols from ketones by using a non-H2 hydrogen source along with metal catalysts. Among homogeneous catalysts, Ru(II) complexes are the most efficient catalysts. In our research, six novel ruthenium(II) complexes bearing bipyridine-based ligands [Ru(L1)Cl2] (1), [Ru(L1)(PPh3)Cl]Cl (2) and [Ru(L2)Cl2] (3) and N-heterocyclic carbene-supported pyridine (NCN) ligands [RuCp(L3)]PF6 (4), [RuCp*(L3)]PF6 (5), and [Ru(p-cymene)(L3)Cl]PF6 (6) (where L1 = 6,6′-bis(aminomethyl)-2,2′-bipyridine, L2 = 6,6′-bis(dimethylaminomethyl)-2,2′-bipyridine and L3 = 1,3-bis(2-methylpyridyl)imidazolium bromide) were synthesised and characterised by NMR spectroscopy, HRMS, and X-ray crystallography. The catalytic transfer hydrogenation of 28 ketones in 2-propanol at 80 °C in the presence of KOtBu (5 mol%) was demonstrated and the effect of ligands is highlighted. The results show that catalyst 1 exhibits improved TH efficiency compared to the commercially available Milstein catalyst and displays higher catalytic activity than 2 due to the steric effect from PPh3. From a combination of kinetic data and Eyring analysis, a zero-order dependence on the acetophenone substrate is observed, implying a rate-limiting hydride transfer step, leading to the proposed inner-sphere hydride transfer mechanism.

Citation

Piyasaengthong, A., Williams, L. J., Yufit, D. S., & Walton, J. W. (2022). Novel ruthenium complexes bearing bipyridine-based and N-heterocyclic carbene-supported pyridine (NCN) ligands: the influence of ligands on catalytic transfer hydrogenation of ketones. Dalton Transactions, 51(1), 340-351. https://doi.org/10.1039/d1dt03240b

• Journal Article Type: Article
• Acceptance Date: Nov 23, 2021
• Online Publication Date: Nov 30, 2021
• Publication Date: Jan 7, 2022
• Deposit Date: Jan 13, 2022
• Publicly Available Date: Nov 30, 2022
• Journal: Dalton Transactions
• Print ISSN: 1477-9226
• Electronic ISSN: 1477-9234
• Publisher: Royal Society of Chemistry
• Peer Reviewed: Peer Reviewed
• Volume: 51
• Issue: 1
• Pages: 340-351
• DOI: https://doi.org/10.1039/d1dt03240b
• Public URL: https://durham-repository.worktribe.com/output/1217178
• Related Public URLs: https://pubs.rsc.org/en/content/articlelanding/2021/dt/d1dt03240b