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.
Cationic fac-[Re(CO) 3 (pz*H)(pypzH)]OTf (pz*H = pyrazole, pzH; 3,5-dimethylpyrazole, dmpzH; indazole, indzH; 3-(2-pyridyl)pyrazole, pypzH) were obtained from fac-[ReBr(CO) 3 (pypzH)] by halide abstraction with AgOTf and subsequent addition of the corresponding pyrazole. Successive deprotonation with Na 2 CO 3 and NaOH gave neutral fac-[Re(CO) 3 (pz*H)(pypz)] and anionic Na{fac-[Re(CO) 3 (pz*)-(pypz)]} complexes, respectively. Cationic fac-[Re(CO) 3and fac-[Re(CO) 3 (pypz) 2 Na] were subjected to photophysical and electrochemical studies. They exhibit phosphorescent decays from a prevalently 3 MLCT excited state with quantum yields (Φ) in the range between 0.03 and 0.58 and long lifetimes (τ from 220 to 869 ns). The electrochemical behavior in Ar atmosphere of cationic and neutral complexes indicates that the oxidation processes assigned to Re I → Re II occurs at lower potentials for the neutral complex compared to cationic complex. The reduction processes occur at the ligands and do not depend on the charge of the complexes. The electrochemical behavior in CO 2 saturated media is consistent with CO 2 electrocatalyzed reduction, where the values of the catalytic activity [i cat (CO 2 )/i cat (Ar)] ranged from 2.7 to 11.5 (compared to 8.1 for fac-[Re(CO) 3 Cl(bipy)] studied as a reference). Controlled potential electrolysis for the pyrazole cationic (3a) and neutral (4a) complexes after 1 h affords CO in faraday yields of 61 and 89%, respectively. These values are higher for indazole complexes and may be related to the acidity of the coordinated pyrazole.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.