A closer look at the formation of bicyclometalated and cyclometalated ruthenium carbonyl complexes

To study steric and electronic factors that affect the C–H activation of Schiff bases by the complex [Ru(PPh3)2(CO)2Cl2], systematic spectroscopic analyses were performed for a family of Ru(II) complexes of type [Ru(PPh3)2(CO)L]. Among eight Schiff bases [H2Ln (n = 1–8)], synthesized by condensation of methyl-4-formyl benzoate with 4-aminoacetophenone, 1-naphthylamine, 2-amino-5-chloropyridine, 8-aminoquinoline, semicarbazide hydrochloride, 2-aminophenol, thiosemicarbazide and 2-aminothiophenol, it was observed that the C–H activation was dependent on the kind as well as the position of the coordinating atoms. The C–H activation of the Schiff bases was most facile in the formation of a Ru-CNO configuration followed by Ru-CNS, Ru-CNN, and Ru-CNC configurations, whereas for a Ru-NC(methine) configuration the activation was the slowest. X-ray crystal structures for five cycloruthenated complexes are reported. Detailed electrochemical studies reveals the redox behavior of the complexes and DFT calculations were performed to obtain geometry optimized structure of all other complexes and to get an insight of the electronic spectral behavior.

To study the effect of steric and the electronic properties of a series of Schiff bases on the C–H activation by ruthenium(II), X-ray crystallographic and spectroscopic analyses were performed for a family of complexes of type [Ru(PPh3)2(CO)L]. It was observed that the activation was dependent on coordination environment as well as the position of the coordinating atoms witin the ligand.Figure optionsDownload as PowerPoint slideHighlights
► C–H activation of eight new Schiff base ligands by Ruthenium(II).
► Crystal structure determination of five of them.
► DFT study of the complexes to understand electronic spectra and to get geometry optimized structure.
► Effect of electronic and steric environment of ligands towards the bonding pattern as well as on the ease of C–H activation.