Luminescent Rhenium(I)tricarbonyl Complexes Containing Different Pyrazoles and Their Successive Deprotonation Products: CO₂ Reduction Electrocatalysts

Abstract

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.

Investigation of Cyclam Based Re‐Complexes as Potential Electrocatalysts for the CO2 Reduction Reaction

“…[23,24] In order to further understand the electrocatalytic CO 2 RR performance of complex 1 a broad variety of modulations of the bpy ligand and furthermore substitutions of bpy for comparable ligand platforms (e. g. pyNHC, pypz, pyiz) were investigated. [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] Among the large number of modified rhenium complexes and within the most studied class, the 4,4'substituted bpy rhenium complexes, the t Bu-derivative Re-(bpy-t Bu)(CO) 3 Cl (bpy-t Bu = 4,4'-di-tert-butyl-2,2'-bipyridine) is particularly noteworthy.…”

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

“…We have shown how a systematic control of the electronic and steric properties of other metal transition complexes containing 1,2-azoles and their derivatives that allows to tune properties of interest, such as their selectivity toward anions, 50 their luminescent properties, 51,52 or their activity as electrocatalysts in CO 2 reduction. 53 Herein we report the synthesis and a thorough characterization of new (1,2-azole)-aquo bis(bipyridyl)ruthenium(II) complexes. The complete characterization of the (1,2-azole)chlorido precursors is also described.…”

“…In addition, the use of 1,2-azole ligands will favor the future tunability of the complexes in both ground and excited states. We have shown how a systematic control of the electronic and steric properties of other metal transition complexes containing 1,2-azoles and their derivatives that allows to tune properties of interest, such as their selectivity toward anions, their luminescent properties, , or their activity as electrocatalysts in CO 2 reduction …”

Scope of Tetrazolo[1,5-a]quinoxalines in CuAAC reactions for the Synthesis of Triazoloquinoxalines, Imidazoloquinoxalines, and Rhenium-complexes thereof

“…Therefore, the obtained triazole and TIQ products were employed to act as ligands in rhenium tricarbonyl complexes. These are especially used as CO2 reduction catalysts [38][39][40] and noninvasive imaging probes [26,41]; examples for the application in organic light-emitting diodes [35] and as photoactive CO-releasing molecule [42,43] have been reported as well.…”