The new chiral ligands (R)-/(S)-N-((1-phenylethyl)carbamothioyl)benzamide (L1/L2), (R)-/(S)-N-((1-phenylethyl)carbamothioyl)thiophene-2-carboxamide (L3/L4), and (R)-/(S)-N-((1-phenylethyl)carbamothioyl)furan-2-carboxamide (L5/L6) were synthesized, characterized, and used to prepare novel chiral Ru(II) complexes. The chiral Ru(II) complexes 1–6 were obtained from reactions between the chiral ligands L1–L6 and [RuCl2(p-cymene)2]2. The complexes were characterized by analytical and spectroscopic (NMR, FT-IR, electronic) techniques. The solid-state structures of the ligands L1 and L3 and complexes 1, 4, and 6 were determined by single-crystal X-ray diffraction methods. In all of the complexes, the ligand is bound to the Ru(II) center only via the sulfur donor atom. This monodentate coordination of the acylthiourea ligands was observed for the first time with ruthenium. The Ru(II) complexes 1–6 all act as efficient catalysts for the asymmetric transfer hydrogenation of aromatic ketones in the presence of 2-propanol and KOH to produce chiral alcohols. All of the catalysts showed excellent conversions of up to 99% and enantiomeric excesses of up to 99%.

The reactions of [RuCl 2 (η 6 -C 6 H 6 )] 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, 1 H NMR and 13 C NMR) studies. The molecular structure of the ligands (L2 and L4) and the complexes (2, 4 and 5) was 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 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 analogues p-cymene complexes. Such enhanced efficiency and the product selectivity for Ru-benzene complexes compared to Ru-p-cymene complexes were rationalized by the computational study.Electronic supplementary information (ESI) available: A table of the X-ray crystallographic data, atomic coordinates in CIF format, the molecular structure of ligands L2 & L4, 1 H NMR and 13 C NMR spectra of all the ligands and complexes, GC and HPLC data are included. Cartesian coordinates, energies, and vibrational frequencies for all the reported structures, and optimized geometries and activation free energies for high energy TSs.

A series of novel N-dibenzosuberene appended aroyl/acylthiourea ligands (L1-L4) and their Ru(II)-benzene complexes (1-4), [RuCl 2 (h 6 -benzene)L] (L = monodentate aroyl/acylthiourea ligand) was synthesized and well characterized. The coordination mode of aroyl/acylthiourea ligand with Ru ion through S (neutral monodentate) donor atom was determined by single crystal X-ray diffraction analysis. In vitro Calf thymus DNA (CT-DNA) and Bovine serum albumin (BSA) interaction of the complexes were investigated by UV-Visible, fluorescence spectroscopic and hydrodynamic methods. The results showed the intercalative mode of binding (in the order of 1 > 4 > 3 > 2) of the Ru(II)-benzene complexes with CT-DNA. The DNA (pUC19) cleavage study showed that the complexes cleaved DNA through a hydrolytic pathway. All the complexes have been thoroughly screened for their cytotoxicity against human liver carcinoma (HepG-2) and lung cancer (A549) cells under in vitro conditions. Complex 1 exhibited significant cytotoxic activity (IC 50 = 46.1 mM) towards HepG-2 cancer cell line. In addition to this, the prepared complexes have been utilized as catalyst precursors for transfer hydrogenation (TH) of ketones, aldehydes and nitro compounds using 2-propanol as a hydrogen source. The TH reactions proceeded with exceptional conversions (up to 99%) and the present catalytic system was extended to substituted aromatic/heterocyclic carbonyl and nitro compounds.

The chiral Ru(ii)-p-cymene complexes are efficient catalysts for the enantioselective reduction of ketones to chiral alcohols.

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