Ru(II) and Ru(III) complexes containing N‐acylthiourea ligands: Supramolecular structures and synthons, reduction, and reaction pathway of aromatic nitro compounds

Abstract

Four ruthenium complexes {[RuCl(CO)(PPh 3 ) 2 L 1 ], [RuCl(CO)(PPh 3 ) 2 L 2 ],[RuCl 2 (PPh 3 ) 2 L 1 ] and [RuCl 2 (PPh 3 ) 2 L 2 ]} supported with N-acylthiourea-based ligands were synthesized. The compounds prepared were characterized by 1 H NMR, 13 C NMR, elemental analysis, UV-vis, and magnetic susceptibility methods. The characterization of the molecular structure of two ruthenium complexes {[RuCl(CO)(PPh 3 ) 2 L 1 ] and [RuCl 2 (PPh 3 ) 2 L 1 ]} was also performed using the single crystal X-ray diffraction method. Single crystal X-ray analyses indicates the existence of different non-covalent interactions between different parts of the molecules, which led to the formation of three-dimensional supramolecular architectures and synthons. The magnetic susceptibility and UV-vis spectra of the prepared ruthenium complexes propose that they are of low-spin states, where Ru(II) is d 6 and Ru(III) is d 5 low spin. These ruthenium compounds functioned as catalysts for the NaBH 4 -mediated reduction of various nitro compounds. The catalytic results show that the [RuCl 2 (PPh 3 ) 2 L] type complexes exhibit higher catalytic activity than the [RuCl(CO)(PPh 3 ) 2 L] type complexes, and [RuCl 2 (PPh 3 ) 2 L 1 ] has high catalytic selectivity and efficiency in a short time (>99 yield with catalyst loading 0.01 mol in 0.5 h). Furthermore, the catalytic activity of [RuCl 2 (PPh 3 ) 2 L 1 ] was investigated using nitrobenzene as a model substrate to understand the reaction pathway, and this study proved that this nitro reduction proceeds via a direct pathway, with the formation of N-hydroxylamine as the main intermediate followed by the occurrence of aniline.