Isomeric complexes of [RuII(trpy)(L)Cl] (trpy=2,2':6',2''-terpyridine and HL=quinaldic acid): preference of isomeric structural form in catalytic chemoselective epoxidation process.

The present work deals with the isomericcomplexes of the molecular composition [RuII(trpy)(L)Cl] in 1 and 2 (trpy = 2,2′:6′,2′′- terpyridine, L = deprotonated form of quinaldic acid, HL). Isomericidentities of 1 and 2 have been established by their single-crystal X-ray structures, which reveal that under the meridional configuration of trpy, O− and N donors of the unsymmetrical L are in trans, cis and cis, trans configurations, respectively, with respect to the Ru−Cl bond. Compounds 1 and 2 exhibit appreciable differences in bond distances involving Ru−Cl and Ru−O1/Ru−N1 associated with L on the basis of their isomericstructural features. In relation to isomer 2, the isomericcomplex 1 exhibits a slightly lower Ru(II)−Ru(III) oxidation potential [0.35 (1), 0.38 (2) V versus SCE in CH3CN] as well as lower energy MLCT transitions [559 nm and 417 nm (1) and 533 nm and 378 nm (2)]. This has also been reflected in the DFT calculation where a lower HOMO−LUMOgap of 2.59 eV in 1 compared to 2.71 eV in 2 is fou...