Half-sandwich Ru(η6-C6H6) complexes with chiral aroylthioureas for enhanced asymmetric transfer hydrogenation of ketones – experimental and theoretical studies

Mary Sheeba, M., Preethi, S., Nijamudheen, A., Muthu Tamizh, M., Datta, A., Farrugia, L. J. and Karvembu, R. (2015) Half-sandwich Ru(η6-C6H6) complexes with chiral aroylthioureas for enhanced asymmetric transfer hydrogenation of ketones – experimental and theoretical studies. Catalysis Science and Technology, 5(10), pp. 4790-4799. (doi: 10.1039/c5cy00774g)

Abstract

The reactions of [RuCl2(η6-C6H6)]2 with chiral aroylthiourea ligands yielded pseudo-octahedral half-sandwich “piano-stool” complexes. All the Ru(II) complexes were characterized by analytical and spectral (UV-visible, FT-IR, 1H NMR and 13C NMR) studies. The molecular structures of the ligands (L2 and L4) and the complexes (2, 4 and 5) were confirmed by single crystal XRD. All the complexes were successfully screened as catalysts for the asymmetric transfer hydrogenation (ATH) of ketones using 2-propanol as the hydrogen source in the presence of KOH. The ATH reactions proceeded with excellent yields (up to 99%) and very good enantioselectivity (up to 99% ee). The scope of the present catalytic system was extended to substituted aromatic ketones and few hetero-aromatic ketones. Density functional theory (DFT) calculations predicted non-classical, concerted transition states for the ATH reactions. The catalytic activity of Ru–benzene complexes toward asymmetric reduction of ketones was significantly higher compared to that of p-cymene complex analogues. Such enhanced efficiency and product selectivity of Ru–benzene complexes compared to those of Ru–p-cymene complexes were rationalized by the computational study.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Farrugia, Dr Louis
• Authors: Mary Sheeba, M., Preethi, S., Nijamudheen, A., Muthu Tamizh, M., Datta, A., Farrugia, L. J., and Karvembu, R.
• College/School: College of Science and Engineering > School of Chemistry
• Journal Name: Catalysis Science and Technology
• Publisher: Royal Society of Chemistry
• ISSN: 2044-4753
• ISSN (Online): 2044-4761
• Published Online: 03 July 2015