Synthesis of the new RU(II) complexes containing DMSO and N-dondor ligands as catalysts for nitrile hydration

Abstract

Thanks to the experience of the research group in the synthesis of ruthenium complexes with dmso and N-donor ligands and their application in catalysis, in this work we have developed new ruthenium complexes using N-donor ligands that have been subsequently evaluated as catalysts for the nitrile hydrolysis reaction. First, two new ruthenium complexes ([2] and [3]) with one or two pzph-OH ligand have been synthesized, together with a ruthenium complex ([4]) with the terpyridine ligand, in all cases with dmso and Cl ligands. The complexes have been characterized using different spectroscopic and electrochemical techniques. With respect to structural characterization, the formation of a single isomer for [2] and [3] complexes has been shown. It should be noted that in the case of complex [2] the crystal structure has been obtained that has been solved by X-ray diffraction analysis. The characterization of complex [4] has also been carried out for one of the isomers that has been obtained in pure form. It should be mentioned that in this case, it is observed the formation of a second isomer for longer reaction times. UV-Vis spectra have been performed in methanol for complexes [2] and [3] and dichlormetane for the [4] complex, where the presence of MLCT and intraligand π-π * bands it evidenced in the three cases, and the corresponding extinction coefficients could be calculated. For complexes [2] and [3] a wavelength shift along the time is observed, possibly due to exchange of one ligand by methanol. Subsequently, the electrochemical properties of the three complexes have been studied by cyclic voltammetry (CV). For complex [2], a reversible wave corresponding to the Ru(III/II) redox pair has been observed. On the contrary, complex [3] exhibits an irreversible wave due to a Ru-dmso bond isomerization process. To demonstrate this fact, an electrochemical study of the two mentioned complexes has been carried out, which has cofirmed that the isomerization process is shown only by complex [3]. Moreover, we also registered the CVs for complex [4], which exhibits a reversible wave; a second wave was observed for longer reaction times evidencing once again the formation of a second isomer. Finally, the catalytic activity in the hydrolysis of nitriles of the complex [3] and [4] has been evaluated using two different substrates, obtaining moderate to high conversions and excellent selectivity for the amide product