New ruthenium complexes containing N- or/and S-donor type of ligands as catalysts for nitrile hydration

Abstract

In this work, we present the synthesis and characterization of new ruthenium complexes with the idea of studying their coordination chemistry, as well as their performance in nitrile hydration reactions. We describe the synthesis and the spectroscopy and redox characterization of new ruthenium compounds, Ru-Cl and Ru-DMSO. These complexes contain the neutral 1,4,7– trithiacyclononane (9S3) and the non-symmetric didentate 2-(3-pyrazolyl)pyridine (pypz- H) ligands. Firstly, we have synthesized the complex [RuIICl2(DMSO)4] [1] and [RuIICl2(9S3)(DMSO)] [2]. Both have been used as starting material for the synthesis of chlorido complex [RuIICl(pypz-H)(9S3)]Cl [3]. Moreover, complex [RuII(9S3)(pypz)(DMSO)](PF6)2 [4] have been also synthesized from complex [3] by replacing chlorido ligand (Cl) by dimethyl sulfoxide ligand (DMSO). The new complexes have been characterized in solid state through elemental analysis and infrared spectroscopy (IR) and in solution through spectroscopic techniques as nuclear magnetic resonance (NMR), ultraviolet visible (UV-Vis) and cyclic voltammetry (CV). The chemical behavior in aqueous solution has been tested for the two complexes Ru-Cl [3] and Ru-DMSO [4] through UV-Vis. In both cases, substitution of chlorido and DMSO ligands for aqua ligand has been observed and consequently we have studied the kinetics of aquation for both complexes. We also have studied the pH-dependent redox properties for the resulting aqua ruthenium complex through a Pourbaix diagram. Finally, the catalytic activity of the complexes in nitrile hydration reaction is evaluated in water using nitriles like benzonitrile and acrylonitrile as substrates. All compounds have shown moderate conversions and high selectivities values towards the corresponding amides