Autor/a:
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Merillas, Beatriz; Cúellar, Elena; Diez-Varga, Alberto; Torroba, Tomás; García-Herbosa, Gabriel; Fernández, Sergio; Lloret-Fillol, Julio; Martín-Alvarez, Jose M.; Miguel, Daniel; Villafañe, Fernando
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Abstract:
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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 Na2CO3 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)3(pz*H)-
(pypzH)]OTf, neutral complexes fac-[Re(CO)3(pz*H)(pypz)],
and fac-[Re(CO)3(pypz)2Na] were subjected to photophysical and
electrochemical studies. They exhibit phosphorescent decays from
a prevalently 3MLCT 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 ReI → ReII 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 CO2 saturated media is consistent with CO2 electrocatalyzed reduction, where the
values of the catalytic activity [icat(CO2)/icat(Ar)] ranged from 2.7 to 11.5 (compared to 8.1 for fac-[Re(CO)3Cl(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. |