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.