(1,2-Azole)bis(bipyridyl)ruthenium(II) Complexes: Electrochemistry, Luminescent Properties, And Electro- And Photocatalysts for CO₂ Reduction

Abstract

New cis-(1,2-azole)-aquo bis­(2,2′-bipyridyl)­ruthenium­(II) (1,2-azole (az*H) = pzH (pyrazole), dmpzH (3,5-dimethylpyrazole), and indzH (indazole)) complexes are synthesized via chlorido abstraction from cis-[Ru­(bipy)2Cl­(az*H)]­OTf. The latter are obtained from cis-[Ru­(bipy)2Cl2] after the subsequent coordination of the 1,2-azole. All the compounds are characterized by 1H, 13C, 15N NMR spectroscopy as well as IR spectroscopy. Two chlorido complexes (pzH and indzH) and two aquo complexes (indzH and dmpzH) are also characterized by X-ray diffraction. Photophysical and electrochemical studies were carried out on all the complexes. The photophysical data support the phosphorescence of the complexes. The electrochemical behavior of all the complexes in an Ar atmosphere indicate that the oxidation processes assigned to Ru­(II) → Ru­(III) occurs at higher potentials in the aquo complexes. The reduction processes under Ar lead to several waves, indicating that the complexes undergo successive electron-transfer reductions that are centered in the bipy ligands. The first electron reduction is reversible. The electrochemical behavior in CO2 media is consistent with CO2 electrocatalyzed reduction, where the values of the catalytic activity [i cat(CO2)/i p(Ar)] ranged from 2.9 to 10.8. Controlled potential electrolysis of the chlorido and aquo complexes affords CO and formic acid, with the latter as the major product after 2 h. Photocatalytic experiments in MeCN with [Ru­(bipy)3]­Cl2 as the photosensitizer and TEOA as the electron donor, which were irradiated with >300 nm light for 24 h, led to CO and HCOOH as the main reduction products, achieving a combined turnover number (TONCO+HCOO– ) as high as 107 for 2c after 24 h of irradiation.

Noble metal-free bis-tridentate benzimidazole zinc(ii) and iron(ii) complexes for selective CO2photoreduction

“…Molecular transition metal complexes have been widely used in CO 2 photoreduction due to their versatile catalytic performances and adjustable chemical structures. 5 For example, noble metal complexes such as Re, 6–8 Ru, 9–11 and Ir 12 used as catalysts for CO 2 photoreduction have been investigated extensively, but the high cost of noble metals is often not conducive to large-scale industrial applications. Therefore, in recent years, more and more noble metal-free complexes such as Fe, 13–16 Co, 17–20 Ni, 21–24 Mn, 25,26 Zn 27,28 and Cu 29,30 have been also employed for CO 2 reduction.…”

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

“…A similar behavior was observed for complexes 1 when the chlorido ligand was replaced by an aquo ligand to generate complexes 2 . 39 The MLCT band can be easily shifted or tuned depending on the 1,2-azolylamidino substituents, as can be easily concluded from the values collected in Table 2 . For example, a comparison of the lower energy bands between complexes derived from the same nitrile leads to the same secuence: indz ( c ) > pz ( a ) > dmpz ( b ) for both complexes 3 (obtained from MeCN) and 4 (obtained from PhCN).…”

“…Chlorido–1,2-azole complexes 1 lead to 1,2-azolylamidino complexes 3 , after the chlorido ligand is removed with silver triflate in the presence of MeCN. The 1,2-azolylamidino complexes derived from PhCN are better obtained after removal of the chlorido ligand from 1 in the presence of H 2 O to generate the aquo complexes 2 , 39 which lead to the 1,2-azolylamidino complexes 4 after addition of PhCN. A catalytic amount of NaOH(aq) was added in order to obtain the 1,2-azolylamidino complexes with pz ( 4a ) and dmpz ( 4c ), whereas no base was needed in order to obtain the indazolylamidino complex ( 4b ).…”

“…The absorption and emission spectral data for all of the complexes herein reported are collected in Tables 2 and 3 . The data for the previously described complexes 1 ( 39 ) are also included in both tables for comparison purposes. The absorption and emission spectra ( Figure 3 ) and the wavelength maxima observed at 298 K in different deaerated solvents are summarized in Figure S19 in the Supporting Information.…”

“…Complexes 1 and 2 were obtained as previously described by us. 39 The rest of the reagents were purchased from the usual commercial suppliers and used as received. Infrared spectra were recorded with a Bruker Tensor 27 FTIR instrument.…”