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

Abstract

New 1,2-azolylamidino complexes cis -[Ru(bipy) 2 (NH=C(R)az*-κ 2 N , 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 1 H, 13 C, and 15 N 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-κ 2 N , 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.

Aquabis(2,2′-bipyridine-κ2 N,N′)(isonicotinamide-κN)ruthenium(II) bis(trifluoromethanesulfonate)

“…Over the last three years, a lot of effort has been directed into studying ruthenium(II) bis(bipyridine) complexes due to their catalytic properties (Griffin et al, 2021), luminescence (Cue ´llar et al, 2021) and biological activity (Al-Wahaib et al, 2021;Allison et al, 2021). Last year, bipyridine ruthenium(II) complexes with halogen-substituted salicylates showed promising in vitro antiproliferative activity against MCF-7 (breast cancer) and U-118 MG (human glioma) cell lines (Schoeller et al, 2023).…”

1,2-Azolylamidino ruthenium(ii) complexes with DMSO ligands: electro- and photocatalysts for CO2 reduction

“…In particular, the electrochemical and luminescence properties of Re( i ) tricarbonyl and cis -bis(bipyridyl)Ru( ii ) complexes containing 1,2-azolylamidino ligands, as well as the photocatalytic behaviour of the latter, have been reported. 11 The same reaction using a nucleobase such as 1-methylcytosine instead of the 1,2-azole has been revealed to be a new method to incorporate biologically relevant substrates into Re( i ) tricarbonyl complexes. 12…”