Using the Alkynyl-Substituted Rhenium(I) Complex (4,4′-Bisphenyl-Ethynyl-2,2′-Bipyridyl)Re(CO)3Cl as Catalyst for CO2 Reduction—Synthesis, Characterization, and Application

Abstract

The synthesis, structure, photophysics, and spectroscopic characterization of an organometallic rhenium multichromophore compound carrying a central 2,2′-bipyridyl acceptor moiety with additional phenylethynyl substituents conjugated at the 4,4′-positions of the acceptor ligands and its effect on the electron density of the central rhenium atom as metal center for CO 2 reduction is reported. The results were compared to fac-(2,2′-bipyridyl)Re(CO) 3 Cl and fac-(5,5′-bisphenylethynyl-2,2′-bipyridyl)Re(CO) 3 Cl. Cyclovoltammetric studies and rotating disk electrochemistry were performed for electrochemical characterization. Ultraviolet and visible (UV-vis) absorption, Fourier transform infrared (FTIR), and luminescence measurements were carried out for a spectroscopic characterization and compared to theoretical calculations at the density functional theory (DFT) level. In addition, the rhenium complex fac-(4,4′-bisphenyl-ethynyl-2,2′-bipyridyl)-Re(CO) 3 Cl was used as a novel catalyst for the electrochemical reduction of CO 2 in homogeneous solution. Results showed an 11-fold increase in the current density under CO 2 saturation and a catalytic second-order rate constant for CO formation of about 560 M −1 s −1 on a Pt working electrode. For further characterization of the CO 2 reduction capabilities, bulk controlled potential electrolysis experiments were performed using a CO 2 -saturated acetonitrile electrolyte solution. The headspace product gas analysis yields CO as main reduction product with faradaic efficiencies of about 12 % over 5-h electrolysis time.

Solvent and Ligand Substitution Effects on the Electrocatalytic Reduction of CO2 with [Mo(CO)4(x,x′‐dimethyl‐2,2′‐bipyridine)] (x=4–6) Enhanced at a Gold Cathodic Surface

“…Despite this, continuing research efforts to produce commercially viable functionalization of CO 2 remains some distance away . Currently, much of the literature regarding molecular electrochemical activation of CO 2 still continues to explore the catalytic properties of the heavier members of Group‐7 (Re), Group‐8 (Ru and Os) and Group‐9 (Rh, and Ir) triads. These “first‐generation” electrocatalysts must be phased out; encouragingly, cheaper alternatives exist within the same groups – Mn substituting Re, Fe substituting Ru and Os, and Co substituting Rh and Ir .…”

Living Long and Prosperous: Productive Intraligand Charge-Transfer States from a Rhenium(I) Terpyridine Photosensitizer with Enhanced Light Absorption

“…1A); in these cases, the absorption is red-shifted due to a stabilization of the ligand-centred π * orbitals (typically the LUMO). 22 While the effects of substitution in the vicinity of the metal centre have been previously described for Re(I) tricarbonyl complexes, [23][24][25][26] further understanding of the effects of substitution far away from the metal centre (Fig. 1B) is needed, and constitutes a promising alternative to fine tune the properties of these complexes.…”

Organic, Organometallic and Bioorganic Catalysts for Electrochemical Reduction of CO2

“…Portenkirchner et al made ac omparatives tudy and investigated the differences in catalytic activity arising from the same group substituted at different positions (compounds 6 and 7, Figure7). [29] The authors once again showed the effect of extended p-conjugation on the absorption characteristics ( Figure 8) noting that this can have an impact on photocatalytic properties. Rotating-disce lectrode measurements in this study showed that the diffusion coefficient of 7 was 2.5 10 À6 cm 2 s À1 ,w hich was in good agreementw ith earlierl iterature values.…”

“…alytic rate dropped drastically to 30 m À1 s À1 .T his difference was attributed to the availability of activated protons on the Pt electrode. [29] Althoughv ariousm olecular catalysts (porphyrins, corroles, cyclams,n aphthyridines, and so forth) with metal centers such as Pd, Ru, Fe, Co, and Ni were investigated, [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49] in the years after the discovery of Lehn'sc atalyst, most research has been focusedo nR e-containing complexes. With an estimated average concentration of 1ppb, Re, together with other noble metals,i so ne of the rarest elements in Earth's crust.…”