Luminescent cis-Bis(bipyridyl)ruthenium(II) Complexes with 1,2-Azolylamidino Ligands: Photophysical, Electrochemical Studies, and Photocatalytic Oxidation of Thioethers

New 1,2-azolylamidino complexes cis-[Ru(bipy)(2)(NH-C(R)az*-kappa N-2,N)](OTf)(2) (R = Me, Ph; az* = pz, indz, dmpz) are synthesized via chloride abstraction after a subsequent base-catalyzed coupling of a nitrile with the previously coordinated 1,2-azole. The synthetic procedure allows the easy obtainment of complexes having different electronic and steric 1,2-azoylamidino ligands. All of the compounds have been characterized by H-1, C-13, and N-15 NMR and IR spectroscopy and by monocrystal X-ray diffraction. Photophysical studies support their phosphorescence, whereas their electrochemistry reveals reversible Ru-II/Ru-III oxidations between +1.13 and +1.25 V (vs SCE). The complexes have been successfully used as catalysts in the photooxidation of different thioethers, the complex cis-[Ru(bipy)(2)(NH-C(Me)dmpz-kappa N-2,N)](2+) showing better catalytic performance in comparison to that of [Ru(bipy)(3)](2+). Moreover, the significant catalytic performance of the dimethylpyrazolylamidino complex is applied to the preparation of the drug modafinil, which is obtained using ambient oxygen as an oxidant. Finally, mechanistic assays suggest that the oxidation reaction follows a photoredox route via oxygen radical anion formation.

Automated summary

In this study, a series of new 1,2-azolylamidino complexes were synthesized and characterized using NMR, IR spectroscopy, and X-ray diffraction. Photophysical and electrochemical studies showed that these complexes exhibit good phosphorescence and reversible oxidation properties. Furthermore, the complexes were successfully used as catalysts in the photooxidation of different thioethers, with one of the complexes showing superior catalytic performance compared to a standard ruthenium complex.