﻿Selective Photocatalytic Conversion of CO2 to Formate by Dimeric Cu(II) Complexes

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Selective Photocatalytic Conversion of CO₂ to Formate by Dimeric Cu(II) Complexes

https://doi.org/10.21203/rs.3.rs-4226361/v1

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Efficient and selective molecular catalysts for visible-light-driven CO₂ conversion to liquid or solid fuels are highly desired to achieve carbon neutralization. Although catalysts utilizing earth-abundant metals have shown some progress for CO and formate production, their conversion efficiency and product selectivity are still quite lacking for practical applications. In this study, we report binuclear Cu complexes of bridging ligands containing two pyridyltriazole units developed during the study of the active sites of related metalloenzymes. Surprisingly, the dimeric complexes with a flexible cavity between two coppers exhibit high activity in catalytic CO₂ reduction, converting CO₂ to formate with high selectivity and efficiency under visible light irradiation. The turnover number and formate selectivity were 43000 and >99%, respectively. The results of the study suggest that a deep understanding of the effect of the ligand environment and structural factors of metal compounds on catalytic activity when used as a catalyst will be helpful.

Physical sciences/Chemistry/Catalysis/Photocatalysis

Physical sciences/Energy science and technology/Renewable energy/Solar energy/Artificial photosynthesis

The rapid growth of global industries and excessive use of fossil fuels have led to serious climate changes, making the efficient conversion of carbon dioxide to useful chemicals and fuels a topic of considerable interest.^1-3 Carbon monoxide and formate are the most common carbon products that can be generated from CO₂, and they have the highest conversion rates in electrochemical and photochemical reactions. Among these products, selective photocatalytic conversion of CO₂ to formic acid has garnered significant attention as a means of carbon capture and light energy storage. This is because formate and formic acid can be stored in solid and liquid forms, and can serve as raw materials for various chemical products in industries.⁴ Formic acid has recently gained attention as a hydrogen storage medium used in fuel cells and as a food source for bacteria that produce alcohol.⁵

Heavy transition metal compounds, such as Ru, Ir, and Re, have been used as CO₂ conversion catalysts for a long time and have shown high reactivity.^6-10

However, scientists in the field have been continuously interested in developing catalysts that use earth-abundant transition metals of Mn, Fe, Co, Ni, and Cu for more environmentally friendly and practical purposes.^11-15 Interestingly, heterobimetallic Mo-Cu and Fe-Ni active sites have been found in a class of CO-dehydrogenase (CODH) known to catalyze the conversion between CO and CO₂.^16-19 Scientists have been trying to find clues as to why Fe-Ni CODH performs reversible conversion of CO and CO₂, while Mo-Cu CODH performs only one-way oxidation of CO. Despite the different reaction characteristics of the two CODHs, it has been found that the metals in the active site of both enzymes play a cooperative role in the binding and activation of CO and CO₂, resulting in high selectivity. Therefore, scientists have synthesized homo- and heterobimetallic compounds to study their reactivity and mechanism for a better understanding of the specificity of the enzyme’s active site and for the development of effective catalysts for artificial photosynthesis.

There are not many biomimetic bimetallic complexes that have been developed for electrochemical and photochemical CO₂ reduction. Recently, a binuclear cobalt cryptate complex was reported to photochemically produce CO at a rate of 17000 turnover number (TON) with a small amount of H₂.^20-21 It has also been reported that the reactivity increases by almost four times when Co-Zn is used instead of Co-Co with the same ligand, demonstrating that the two metals cooperate in the reactivity and selectivity for CO production. In another example, a dinuclear Co complex using a ligand with two qpy (qpy = 2,2′:6′,2′′:6′′,2′′′-quaterpyridine) connected by xanthene showed that CO₂ binds between the two metals, and under reaction conditions, CO, formate, and H₂ were obtained with a total TON of less than 1100, demonstrating varying selectivity toward CO and formate.²²

Copper compounds are less commonly developed for photochemical CO₂ reduction. A mononuclear Cu complex with qpy ligand showed 97 % selectivity and produced 12400 TON of CO.²³ A Cu-Cu complex with qpy ligand and xanthene bridge produced formate and CO in a ratio of almost 2:1 with 766 TON under visible light energy.²⁴ Although hydride formation between the two Cu atoms was proposed in this study, the detailed mechanism of the two product formations remains to be elucidated. Therefore, more research on dinuclear metal complexes is needed for a better understanding of the high reactivity and detailed mechanism.

We has also been studying mononuclear and dinuclear metal complexes to understand the reactivity of the active sites of metalloenzymes and to develop efficient practical catalysts. Recently, we reported the production of formate with high selectivity of 14000 TON in a visible light active CO₂ conversion reaction using a Ni complex with a S-rich ligand environment.¹⁴ During this process, we became interested in a ligand called m-xpt containing two pyridyltriazole units connected with m-xylylene group as a spacer. Using m-xpt, researchers synthesized dinuclear Cu(II) complexes.²⁵ These complexes, [Cu₂(m-xpt)₂X₂]ⁿ⁺ (X = H₂O (1), Clˉ (2)), were then employed in the chemical reduction of CO₂ using ascorbate.^25-26 To the best of our knowledge, no electrochemical and photochemical H₂production and CO₂ reduction have been reported with any Cu₂(m-xpt)₂ complexes until now. In this study, the reactivity and reaction mechanism of complex 1, 2, and complexes containing dioxane were investigated. Surprisingly, complex 1 generated formate with high selectivity and conversion in the CO₂ photoreduction. This was the highest TON for formate among molecular catalysts using low transition metals known to date. The detailed reaction mechanism is also presented along with these results.

Crystal structures and spectroscopic properties of Cu(II) complexes with dioxane. We have obtained single crystals of [Cu₂(m-xpt)₂X₂(dioxane)]ⁿ⁺ (X = H₂O (1_do), Clˉ (2_do)) by incorporating 1,4-dioxane into complexes 1 and 2. The X-ray analyses of 1_do and 2_do showed that the two copper(II) centers had distorted octahedral geometries and P21/n and C2/c symmetries, respectively (Fig. 1, Table S1-S6). The Cu-Cu distances were 7.692 and 7.935 Å for 1_do and 2_do, respectively, which were longer than those of complexes 1 and 2 (7.244 and 7.615 Å, respectively).²⁵ These results indicated that dioxane enlarged the cavities and increased the Cu-Cu lengths. The Cu-Cu distance of 2_do with the stronger ligand Clˉ was longer than that of 1_do with water. As further evidence, the Cu-Cu distance (5.421 Å) in [Cu₂(m-xpt)₂(oxalate)]²⁺, where oxalate bridged bidentately to each Cu(II),²⁴ was much shorter than those of 1_do and 2_do, suggesting that the size and weak coordination of dioxane affect the Cu-Cu distances and the size of the cavity can vary greatly depending on the additives that go into the cavity. The Cu-O_dioxane distances of 1_do and 2_do were 2.55 and 2.67 Å, respectively. The Cu(II)-O_H2O distance of 2.23 Å in 1_do was also longer than that of complex 1 and other Cu(II)-OH₂ complexes (1.86–1.93 Å).^27–28 The Cu(II)-Cl distance of 2.50 Å in 2_do was also unusually longer than that of other Cu(II)-Cl complexes (2.28–2.37 Å) with octahedral structures.^29–30 These data implied that H₂O and Clˉ were weakly bound to Cu(II) and could be easily replaced by other external reagents.

Complexes 1–2 were used for most following photochemical experiments, unless otherwise stated. The absorption spectra of complexes 1 and 2 exhibit Cu(II) d-d bands at λ_max = 686 nm (ε = 92.7 M^− 1 cm^− 1) and 683 (ε = 90.3), respectively, in DMF/EtOH (see Fig. 2a and Supplementary Fig S1). The absorption bands of complexes 1_do and 2_do shifted slightly to 688 and 684, respectively (Fig S2). The ¹H-NMR spectra of complexes 1, 2, 1_do, and 2_do had all the proton peaks in the paramagnetic region, as typical for Cu(II) complexes (Fig. 2b and Fig S3). These results suggest that the two Cu centers of each complex are weakly coupled, as expected from the unconjugated bridging ligand and the large distances between the coppers.

Photocatalytic CO₂ conversion with complexes 1 and 2. We tested the photocatalytic reactions of complexes 1 and 2 with eosin Y (EY) and triethanolamine (TEOA) under a Xe lamp/420-nm cut-off filter under 1 atm CO₂ in buffer (pH = 10.7). We measured the products by GC and HPLC analyses of the gas and solution after the photolyses. Remarkably, complexes 1 and 2 converted CO₂ to formate very efficiently, with turnover numbers (TONs) of 43000 and 38000 at 40 h, respectively (Fig. 3a and Fig S4). We did not detect any other carbon products, such as CO and oxalate, or H₂ in any of the reactions. Adding Hg did not change the formate production with 1, which implies that complex 1 was a molecular catalyst for the photocatalytic CO₂ reduction (Fig S5). These results show that the photochemical CO₂ reduction with 1 and 2 is highly selective for formate and that the TON of formate based on complex 1 is the highest among those reported with earth-abundant metal complexes.^11–14 These results suggest that Cu(II) complexes related to complexes 1 and 2 could be promising catalysts for the photochemical CO₂ conversion in artificial photosynthetic systems.

We examined the effect of dioxane in the cavity of complex 1 on the CO₂ photoreduction. Complex 1_do showed slightly higher reactivity than 1 in the 8 h reaction (Fig S6). The data show that complex 1_do has a similar high reactivity to complex 1 and that the dioxane in the cavity does not interfere with the interaction between the reactive Cu intermediate and the CO₂ substrate. The slightly higher reactivity of 1_do suggests the need for further studies to undersand the additive effects of the cavity on the CO₂ reactivity of the Cu dimers. We will address this topic in a separate publication.

Electrochemical properties of complexes 1 and 2. We studied the electrochemical properties of complex 1 by cyclic voltammetry (CV) to gain more insight into the photocatalytic CO₂ reduction. The reduction current of complex 1 increased significantly under CO₂ (Fig. 3c). We only observed the catalytic current under CO₂, which implies that CO₂ reacted effectively with a reactive Cu intermediate in the electrochemical process. The onset potential of the catalytic current was about − 1.1 V (vs SCE), which suggests that photochemically formed EY* (E^o_ox= -1.11 V vs SCE) could reduce 1 to generate Cu(II)-H species as a reactive intermediates.³¹ We confirmed this by quenching EY* with complex 1 (Fig. S7), which showed an electron-transfer process from EY* to 1. We also measured the cyclic voltammograms of complex 1 with increasing amounts of acetic acid (Fig. 3d). The acid addition produced catalytic reduction waves with an onset potential of -1.1 V. The catalytic current (i_c) had a linear correlation with the acid concentration at a scan rate of 100 mV·s^− 1, which indicates the second-order dependence of protons and the generation of Cu(II)-H species. The catalytic peak current was proportional to the square root of the scan rate, which means that the catalytic process was diffusion-limited (Fig S8). Other low transition metal complexes had similar electrochemical data and interpretations.^12–14

Photochemical H₂ photoproduction with complexes 1 and 2. We investigated the H₂ production by the photolysis of Cu complexes with EY and TEOA at pH 10.7 under CO₂ and Ar to gain further insight into the CO₂ photoreduction mechanism. Complexes 1 and 2 produced 510 and 420 TON of H₂, respectively, for 8 h under Ar, but the H₂ photoproduction was almost completely inhibited under CO₂ (Fig. 3b and S9). These data indicate that the proton and CO₂ reduction steps share the same reactive intermediate and that the CO₂ reaction prevails over the proton reduction. Interestingly, complex 1_do also produced more hydrogen than 1 (Fig S10), as we observed in the CO₂ photoreduction above. The H₂ photoproduction with 1_do was also completely suppressed under CO₂. However, this observation suggests that the reaction intermediate of complex 1_do remains accessible to CO₂ even in the presence of dioxane.

Further mechanistic studies for photocatalytic CO₂ reduction. The reduction of complex 1 was studied with sodium ascorbate as a reducing agent. Upon addition of ascorbate, the blue Cu(II) complex 1 immediately changed to yellow due to the formation of Cu(I) species in DMF/H₂O (Fig. 2c), as reported in DMF.²⁵ The reduction of Cu(II) to Cu(I) was also evidenced by the EPR study. The Cu(I) intermediates (1a) generated from complex 1 with ascorbate appeared EPR-silent (Fig. 2d). Then, the yellow solution of 1a changed back to blue upon exposed to CO₂, showing a band of product 1b at 705 nm (Fig. 2a). The EPR spectrum of the stable 1b indicates a Cu(II) species and its NMR spectrum shows paramagnetic peaks similar to 1 (Fig. 2b, 2d). Complex 1b is supposed to be Cu(II)-formate coordinated by formate produced by CO₂ reduction. Complex 1b can be reduced back to 1a by ascorbate for another catalytic cycle (Fig. 2c). In addition, intermediate 1a was progressively converted to a light green species under Ar under the same conditions and the conversion was faster upon treatment of acid. The EPR of the light green species (λ_max = 701 nm) also showed Cu(II) which is obviously different from 1b (Fig S11). Furthermore, the catalytic cycle including 1a and 1b was evidenced by observing the formate production after reaction of 1 with 200 equiv ascorbate under CO₂ for 3 h. The formate production was measured as 25 TON indicating the presence of the catalytic cycle. Such conversion of 1_do to a yellow Cu(I) species was similarly observed (Fig S12).

In the catalytic cycle for CO₂ photoconversion with complex 1, Cu(II)-H intermdiates (1c) were expected to be generated (Scheme 1). The presence of 1c was confirmed by the catalytic currents in the presence of acid under Ar (Fig. 3d). It was previously reported that the catalytic currents resulted from the catalytic reactions of metal-H species with protons for other metal complexes.^11–15 The generation of such Cu(II)-H intermediates in the CO₂ photoreduction was also supported by the catalytic current observed with the similar onset potential (Fig. 2d). 10-Methylacridinium (Acr⁺) salts, which trap hydrides from metal-hydrides, were used to investigate their impact on the expected Cu(II)-H intermediates in the photocatalytic hydrogen generation reaction (Fig S13).^32–33 It was observed that the concentration of Acr⁺ directly influenced the rate of hydrogen production, suggesting the indirect presence of Cu(II)-H intermediates. A further evidence for the generation of 1c was provided by kinetic isotope effect (KIE) measurements of photochemical CO₂ conversion with 1 in DMF/H₂O (or D₂O). An inverse KIE of 0.74 was observed with complex 1, suggesting an insertion of CO₂ into Cu(II)-H species (Fig S14a). Such inverse KIEs were also observed for olefin or CO₂ insertion reactions with other transition metal-hydride intermediates,^14,34–35 and the conversion of CO₂ to CO using Fe and Co complexes showed normal KIE values.^36–37

To study the changes of complex 1 in the photocatalytic cycle for CO₂ reduction, ¹H-NMR spectra were recorded before and after CO₂ photoreduction. The NMR spectrum of a solution after the photocatalytic reaction of complex 1 with EY and TEOA under CO₂ for 12 h showed paramagnetic peaks similar to those of 1b generated with ascorbate above (Fig. 2b). The paramagnetically shifted protons of 1 were also observed after the photoreaction (Fig. 2b), indicating the recovery of the catalyst. However, the shift of the peak at 17.5 ppm to 14.2 after the photoreaction was attributed to the coordination of formate. Indeed, the spectrum of 1 obtained in the presence of 20 equiv formate also showed such a shifted paramagnetic peak (Fig S15). These NMR data also showed that complex 1 was still remained active after several turnovers in the photocatalytic CO₂ reaction, corresponding to the observation of high TONs for the formate production. All paramagnetic peaks of 1 were converted to diamagnetic ones in 1a due to the reduction to Cu(I) intermediates (Fig. 2b). Moreover, the addition of ascorbate to complex 1 in the presence of formate also led to complete conversion to diamagnetic Cu(I) species, indicating that the Cu complex after photoreaction was still active even in the presence of formate as the reaction product. The yellow Cu(I) intermediate is converted back to Cu(II) upon reaction with HBF₄ (Fig S16).

We propose a mechanism for visible light-driven CO₂ reduction based on the observations described above using dimeric Cu(II) complexes 1 and 2 (Scheme 1). The Cu(II) centers are reduced to Cu(I) intermediates by receiving electrons from photoexcited EY (EY*), as confirmed by absorption, EPR, and NMR studies with ascorbate. Then, the Cu(I) centers are further converted to Cu(II)-H intermediates by receiving more electrons from EY* with proton coupling. The formation of Cu(II)-H species is supported by the proton-dependent catalytic currents, proton photoreduction and its normal kinetic isotope effect (KIE = 1.8) for H₂ (Fig S14b). Then, the CO₂ insertion into Cu(II)-H intermediates occurs, which was evidenced by an inverse kinetic isotope effect. Finally, the Cu(II)-formate complex releases formate and returns to the Cu(I) state by getting another electron from EY*, completing and continuing the catalytic cycle.

Dimeric Cu(II) complexes that use m-xpt as a bridging ligand have demonstrated interesting reactivity for CO₂ reduction, producing formate selectively as a highly efficient photocatalytic system. One of the catalysts provided the highest turnover conversion compared to other earth-abundant metal molecular catalysts ever reported. The results, including absorption, EPR, NMR, CV, and kinetic isotope studies, provide insight into the mechanism of photocatalytic CO₂ conversion via Cu(II)-H intermediates. The consecutive electron transfers from the photoexcited EY to Cu centers produce Cu(II)-H intermediates through Cu(I) species, which are responsible for CO₂ photoreduction. However, it has not been demonstrated that the catalytic process is controlled by the two Cu atoms acting synergistically. It is reasonably understood that two Cu centers are too far apart, and the bridging ligands are not conjugated electronically. However, our studies demonstrate that dimeric Cu(II) complexes coordinated by a flexible bridging ligand provide high reactivity and selectivity for CO₂ photoconversion.

The future research plan includes the following: (i) What is the reason for the high reactivity and selectivity of dinuclear Cu complexes with flexible bridging ligands that bind to metals in a bidentate mode? (ii) What is the relationship between the two Cu atoms for their high reactivity and selectivity? (iii) What role do the non-coordinated N atoms of m-xpt in dinuclear Cu complexes play for their reactivities? (iv) What reactivity will dinuclear Co complexes with the same structure exhibit? We will strive to find answers to these questions. We hope that our research results will contribute to a better understanding of metalloenzymes that exhibit unique reactivity and to the development of practical catalysts that show superior reactivity for artificial photosynthesis.

Materials and methods. Reagents purchased from Aldrich were used without further purification, unless otherwise specified. We purified water using a MilliQ purification system. Crystallographic analyses were conducted at the Crystallographic Laboratory of Ewha Womans University using a SMART APEX CCD equipped with a Mo X-ray tube. UV-vis absorption spectra were recorded on a Hewlett Packard 8453 spectrophotometer. NMR measurements were performed using a Bruker Co. AVANCE III 3000 FT-NMR (300 MHz) at the National Research Facilities and Equipment Center (NanoBio & Energy Materials Center) at Ewha Womans University. Emission spectra were collected on a Perkin-Elmer LS 55 luminescence spectrophotometer. Electrospray ionization mass spectra (ESI-MS) were obtained using a Thermo Finnigan LCQTM Advantage MAX quadrupole ion trap instrument located in San Jose, CA, USA. Samples were infused directly into the source at 25 µL/min with a syringe pump. The spray voltage was set at 4.7 kV and the capillary temperature was maintained at 70°C. Elemental analyses for carbon, nitrogen, and hydrogen were carried out using a Flash EA 1112 elemental analyzer (thermo) at the Organic Chemistry Research Center of Sogang University, Korea.

Preparation of complexes 1 and 2. Complexes 1 and 2 were prepared by using a literature procedure.²⁵

Preparation of [Cu₂(m-xpt)₂(dioxane)(H₂O)₂]·(NO₃)₄(1_do). Complex 1_do was synthesized according to the literature containing the procedure of complex 1.²⁵ To a stirred solution of Cu(NO₃)₂·3H₂O (0.10 mmol) in dry acetonitrile (5.0 mL), m-xpt (0.1 mmol) dissolved in chloroform (5.0 mL) was added dropwise and the mixture was stirred at ambient temperature for 6 h. Green precipitates were then filtered and washed several times with acetonitrile and chloroform. The solid was dried to afford a green powder as a product in 69% yield. After slow evaporation of a solution of water/dioxane containing complex 1, blue colored diffraction quality single crystals of 1_do were obtained. ESI-MS: m/z 457.13 [Cu₂(m-xpt)₂]²⁺ (calcd 457.11), 519.17 [Cu₂(m-xpt)₂(NO₃)₂]²⁺ (calcd 519.18) (Fig S17a). Calculated (Calcd) for [Cu₂ (m-xpt)₂ (dioxane) (H₂O)₂]·(NO₃)₄: C 44.76, H 3.76, N 21.75. Found C44.60, H 3.62, N 21.95.

Preparation of [Cu₂(m-xpt)₂(dioxane)Cl₂]·Cl₂(2_do). Complex 2_do was synthesized in a similar manner to 1_do. The only difference was that CuCl₂·2H₂O (0.10 mmol) was used instead of Cu(NO₃)₂·3H₂O. After washing the precipitate with acetonitrile and chloroform, the crude product was dried under vacuum to give a green powder in 75% yield. X-ray quality crystals were grown by diffusing diethyl ether into an acetonitrile solution of 2_do in the presence of dioxane at room temperature. ESI-MS: m/z 457.13 [Cu₂(m-xpt)₂]²⁺ (calcd 457.11), 492.08 [Cu₂(m-xpt)₂Cl₂]²⁺ (calcd 492.06) (Fig S17b). Calcd for [Cu₂(m-xpt)₂(dioxane)Cl₂]·Cl₂: C 50.31, H 3.87, N 19.56. Found: C 50.16, H 3.74, N 19.74.

Electrochemical measurements. Cyclic voltammetry (CV) and linear sweep voltammetry experiments were performed using a CH instrument galvanostat/potentiostat (CHI630C). The reference electrode was Ag/AgCl, the working electrode glassy carbon, and the counter electrode platinum wire. All experiments were conducted in a DMF/EtOH (9:1) solvent with 0.1 M NBu₄PF₆ as the supporting electrolyte. The solutions were purged with Ar or CO₂ for 15 min before the corresponding experiments.

Photocatalytic CO₂ reduction. To perform a typical photochemical CO₂ reaction, a solution of 5.0 µM 1, 400 mM TEOA, and 2 mM EY in EtOH/ H₂O was prepared in a quartz cuvette cell with a capacity of 24 mL. The cell was sealed with a septum, and the solutions were purged with CO₂ for 15 min. The solution was then irradiated using a 450W Xe lamp of Arc Light Source Instrument (Ind. Newport corporation, Oriel product line M-69920) with a 420 nm cut-off filter. The product formate was detected and quantitated using HPLC (YL 9100, Youngin Inc., Korea) on a column Agilent Hi-plex H. Formic acid was quantitated based on a calibration curve (Fig S4) and the turnover number (TON) of formic acid was calculated based on (mol of formate)/(mol of complex 1). In addition, the TON to formate generated after the photochemical reaction was verified by comparing H-NMR integration with that of standard formate.

Measurements of hydrogen photoproduction. In a typical experiment of photocatalytic reactions, each sample was prepared in a 28 mL glass cell with volume of 2 mL of deaerated phthalic acid buffer (50 mM, pH 4.5) and MeCN (1:1 v/v) sample solution. The cell was sealed with a septum and degassed by bubbling argon through the solution for 7 min at room temperature. The samples were irradiated by a 450 W Xenon Arc Light Source Instrument (Ind. Newport corporation, Oriel product line M-69920) with a 420 nm cut-off filter. The amounts of hydrogen produced were determined by gas chromatography using a DS6200 Gas chromatograph (Donam Instrument Inc., Korea) with a Carbosphere 80/100 Mesh, 6ft x 1/8” OD SS Column (Alltech, Part No.5682PC). The headspace gas of the cell was analyzed using a GC instrument, and H₂ was quantitated based on a calibration curve.

Competing financial interests. The authors declare no competing financial interests.

Dalle, K. E. et al. Electro- and solar-driven fuel synthesis with first row transition metal complexes. Chem. Rev. 119, 2752−2875 (2019).
Aresta, M., Dibenedetto, A. & Angelini, A. Catalysis for the valorization of exhaust carbon: from CO₂ to chemicals, materials, and fuels. technological use of CO₂. Chem. Rev. 114, 1709−1742 (2014).
Morris, A. J., Meyer, G. J. & Fujita, E. Molecular approaches to the photocatalytic reduction of carbon dioxide for solar fuels. Acc. Chem. Res. 42, 1983−1994 (2009).
Mellmann, D., Sponholz, P., Junge, H. & Beller, M. Formic acid as a hydrogen storage material development of homogeneous catalysts for selective hydrogen release. Chem. Soc. Rev. 45, 3954−3988 (2016).
Yu, X. & Pickup, P. G. Recent advances in direct formic acid fuel cells (DFAFC). J. Power Sources 182, 124−132 (2008).
Morimoto, T. et al. CO₂ capture by a rhenium (I) complex with the aid of triethanolamine. J. Am. Chem. Soc. 135, 16825−16828 (2013).
Reithmeier, R. O., Meister, S., Siebel, A. & Rieger, B. Synthesis and characterization of a trinuclear iridium(III) based catalyst for the photocatalytic reduction of CO₂. Dalton Trans. 44, 6466−6472 (2015).
Sato, S., Morikawa, T., Kajino, T. & Ishitani, O. A highly efficient mononuclear iridium complex photocatalyst for CO₂ reduction under visible light. Angew. Chem. Int. Ed. 52, 988–992 (2013).
Mouchfiq, A., Todorova, T. K., Dey, S., Fontecave, M. & Mougel, V. A bioinspired molybdenum–copper molecular catalyst for CO₂ electroreduction. Chem. Sci. 11, 5503–5510 (2020).
Tamaki, Y., Morimoto, T., Koike, K. & Ishitani, O. Photocatalytic CO₂ reduction with high turnover frequency and selectivity of formic acid formation using Ru(II) multinuclear complexes. Proc. Natl. Acad. Sci. U. S. A. 109, 15673−15678 (2012).
Khalil, M., Gunlazuardi, J., Ivandini, T. A. & Umar, A. Photocatalytic conversion of CO₂ using earth-abundant catalysts: A review on mechanism and catalytic performance. Renew. Sust. Energ. Rev. 113, 109246 (2019).
Boutin, E. et al. Molecular catalysis of CO₂ reduction: recent advances and perspectives in electrochemical and light-driven processes with selected Fe, Ni and Co aza macrocyclic and polypyridine complexes. Chem. Soc. Rev. 49, 5772−5809 (2020).
Kojima, T. Photocatalytic carbon dioxide reduction using nickel complexes as catalysts. ChemPhotoChem 5, 512−520 (2021).
Lee, S. E. et al. Visible-light photocatalytic conversion of carbon dioxide by Ni(II) complexes with N₄S₂ coordination: highly efficient and selective production of formate. J. Am. Chem. Soc. 142, 19142−19149 (2020).
Wang, Y., Liu, T., Chen, L. & Chao, D. Water-assisted highly efficient photocatalytic reduction of CO₂ to CO with noble metal-free bis(terpyridine)iron(II) complexes and an organic photosensitizer. Inorg. Chem. 60, 5590–5597 (2021).
Jeoung, J.-H. & Dobbek, H. Carbon dioxide activation at the Ni,Fe-cluster of anaerobic carbon monoxide dehydrogenase. Science 318, 1461−1464 (2007).
Appel, A. M. et al. Frontiers, opportunities, and challenges in biochemical and chemical catalysis of CO₂ fixation. Chem. Rev. 113, 6621−6658 (2013).
Mondal, B., Song, J., Neese, F. & Ye, S. Bio-inspired mechanistic insights into CO₂ reduction. Curr. Opin. Chem. Biol. 25, 103−109 (2015).
Dobbek, H., Gremer, L., Kiefersauer, R., Huber, R. & Meyer, O. Catalysis at a dinuclear [CuSMo(O)OH] cluster in a CO dehydrogenase resolved at 1.1-Å resolution. Proc. Natl. Acad. Sci. U. S. A. 99, 15971−15976 (2002).
Ouyang, T., Huang, H.-H., Wang, J.-W., Zhong, D.-C. & Lu, T.-B. A Dinuclear Cobalt Cryptate as a Homogeneous Photocatalyst for Highly Selective and Efficient Visible-Light Driven CO₂ Reduction to CO in CH₃CN/H₂O Solution. Angew. Chem. Int. Ed. 60, 756 –761 (2017).
Ouyang, T. et al. Dinuclear metal synergistic catalysis boosts photochemical CO₂-to-CO conversion. Angew. Chem. Int. Ed. 57, 16480−16485 (2018).
Guo, Z. et al. Selectivity control of CO versus HCOO⁻ production in the visible-light-driven catalytic reduction of CO₂ with two cooperative metal sites. Nat. Catal. 2, 801−808 (2019).
Guo, Z. et al. Photocatalytic conversion of CO₂ to CO by a Copper(II) quaterpyridine complex. ChemSusChem 10, 4009–4013 (2017).
Bharti, J. et al. Visible-light-driven CO₂ reduction with homobimetallic complexes. cooperativity between metals and activation of different pathways. J. Am. Chem. Soc. 145, 25195−25202 (2023).
Pokharel, U. R., Fronczek, F. R. & Maverick, A. W. Reduction of carbon dioxide to oxalate by a binuclear copper complex. Nat. Commun. 5, 1−5 (2014).
Khamespanah, F. et al. Oxalate production via oxidation of ascorbate rather than reduction of carbon dioxide. Nat. Commun. 12, 1997 (2021).
Simmons, C. J. et al. temperature dependence of the crystal structure and g-values of trans-diaquabis(methoxyacetato)Copper(II): evidence for a thermal equilibrium between complexes with tetragonally elongated and compressed geometries. Inorg. Chem. 50, 4900–4916 (2011).
Clegg, W., Holcroft, J. M. & Martin, N. C. Copper pyromellitates: a complex story. CrystEngComm 17, 2857–2871 (2015).
Brotherton, W. S. et al. Tridentate complexes of 2,6-bis(4-substituted-1,2,3-triazol-1-ylmethyl)pyridine and its organic azide precursors: an application of the copper(II) acetate-accelerated azide–alkyne cycloaddition. Dalton Trans. 40, 3655−3665 (2011).
Starosta, W. & Leciejewicz, J. Catenated molecular pattern in the crystal structure of a copper(II) complex with pyrazine-2,6-dicarboxylic acid and chloride ligands. J. Chem. Crystallogr. 35, 861−864 (2005).
Srivastava, V. & Singh, P. P. Eosin Y catalysed photoredox synthesis: a review. RSC Adv. 7, 31377−31392 (2017).
Liu, J. et al. New class of hydrido Iron(II) compounds with cis-reactive sites: combination of iron and diphosphinodithio ligand. Chem. Asian J. 11, 2271–227 (2016).
Zhu, X.-Q. et al. Thermodynamics and kinetics of the hydride-transfer cycles for1-aryl-1,4-dihydronicotinamide and its 1,2-dihydroisomer. Chem. Eur. J. 9, 3937–3945 (2003).
Sullvan, B. P. & Meyer, T. J. Kinetics and mechanism of carbon dioxide insertion into a metal-hydride bond. A large solvent effect and an inverse kinetic isotope effect. Organometallics 5, 1500−1502 (1986).
Doherty, N. M. & Bercaw, J. E. Kinetics and mechanism of the insertion of olefins into transition metal-hydride bonds. J. Am. Chem. Soc. 107, 2670−2682 (1985).
Ahmed, M. E., Rana, A., Saha, R., Dey, S. & Dey, A. Homogeneous electrochemical reduction of CO₂ to CO by a cobalt pyridine thiolate complex. Inorg. Chem. 59, 5292−5302 (2020).
Wang, Y., Liu, T., Chen, L. & Chao, D. Water-assisted highly efficient photocatalytic reduction of CO₂ to CO with noble metal-free bis(terpyridine)iron(II) complexes and an organic photosensitizer. Inorg. Chem.60, 5590−5597 (2021).

Scheme 1 is available in the Supplementary Files section.

There is NO Competing Interest.

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Scheme1.png
Scheme. 1 | Proposed mechanism for photochemical CO₂ conversion using complex 1, with EY* representing the photoexcited state of EY.

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Selective Photocatalytic Conversion of CO₂ to Formate by Dimeric Cu(II) Complexes

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