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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.

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


Authors

Akkharadet Piyasaengthong

Luke J. Williams

Dmitry S. Yufit



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 Mar 28, 2024
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
Related Public URLs https://pubs.rsc.org/en/content/articlelanding/2021/dt/d1dt03240b

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