Piano-stool Ru(II)-benzene complexes bearing D/L-alanine derived chiral aroylthiourea ligands for asymmetric transfer hydrogenation of ketones in water

Abstract

The new water soluble chiral Ru(II)-benzene complexes of the type [RuCl 2 (η 6-C 6 H 6)L] were obtained from the reactions between [RuCl 2 (η 6-C 6 H 6)] 2 and the chiral aroylthiourea ligands (L) derived from unprotected D/L-alanine and characterized. The solid-state structure of representative complexes was confirmed by single crystal X-ray diffraction technique. The Ru(II)-benzene complexes catalyzed the asymmetric transfer hydrogenation (ATH) of aromatic ketones to their enantiopure secondary alcohols. The reactions were carried out in the presence of formic acid-triethylamine mixture in water, and the product alcohols were obtained with excellent conversions (up to 99%) and enantiomeric excesses (up to 99%). The scope of the catalytic system was extended to various aromatic ketones. The catalytic activity of the present water-soluble Ru-benzene complexes toward enantioselective reduction of ketones was considerably higher than that of p-cymene analogues in water.

Recent trends in chemistry, structure, and various applications of 1-acyl-3-substituted thioureas: a detailed review

“…Sheeba et al 59 prepared novel water-soluble half-sandwich chiral Ru( ii )-benzene complexes 81(a, b) and 82(a–d) using chiral aroyl thiourea ligands 79, 80 derived d / l -alanine and [RuCl 2 (η 6 -C 6 H 6 )] 2 78 in toluene as shown in Scheme 25 . These complexes were characterized, and their solid-state structures were confirmed.…”

“…Octahedral diamagnetic complexes 69a-j of substituted thiourea ligands and cobalt metal were synthesized by Barnard et al 54 The synthesis of complexes 69a-j involves the reaction between ligand 68 and CoCl 2 $6H 2 O in ethanol at room temperature Scheme 20. These complexes were completely characterized by using 1 H, 13 C and 59 Co NMR into congurational isomers, and the research group also reported the crystal structures of some of the isolated forms.…”