Water-Assisted Highly Efficient Photocatalytic Reduction of CO₂ to CO with Noble Metal-Free Bis(terpyridine)iron(II) Complexes and an Organic Photosensitizer

Abstract

Photocatalytic CO 2 reduction reaction is believed to be a promising approach for CO 2 utilization. In this work, a noble metal-free photocatalytic system, composed of bis(terpyridine)iron(II) complexes and an organic thermally activated delayed fluorescence compound, has been developed for selective reduction of CO 2 to CO with a maximum turnover number up to 6320, 99.4% selectivity, and turnover frequency of 127 min −1 under visible−light irradiation in dimethylformamide/H 2 O solution. More than 0.3 mmol CO was generated using 0.05 μmol catalyst after 2 h of light irradiation. The apparent quantum yield was found to be 9.5% at 440 nm (180 mW cm −2 ). Control experiments and UV−vis−NIR spectroscopy studies further demonstrated that water strongly promoted the photocatalytic cycle and terpyridine ligands rather than Fe(II) were initially reduced during the photocatalytic process.

Noble metal-free bis-tridentate benzimidazole zinc(ii) and iron(ii) complexes for selective CO2photoreduction

“…In continuation of interest on metal complexes with tridentate ligands, 37–39 we recently found terpyridine-based iron complexes could be used for light-driven reduction of CO 2 when an organic thermally activated delayed fluorescence (TADF) compound 4CzIPN was used as the light-harvesting photosensitizer. 40–42 In similarity to 2,2′:6′,2′′-tripyridine, 2,6-bis(2-benzimidazole)pyridine has both strong σ-donor (benzimidazole unit) and π-acceptor (pyridine ring) properties, which allows them to form various metal complexes that might be also used for CO 2 photoreduction like terpyridine-based metal complexes. 43,44 Those benzimidazole-based tridentate metal complexes have been studied in numerous research fields such as sensing, 45 spin crossover, 46–48 and anticancer agents.…”

Organic Photosensitizers for Catalytic Solar Fuel Generation

“…As the majority of the solar radiation (44%) reaching the Earth’s surface is visible light, in recent years, photocatalytic CO 2 reduction was explored using organic PS which exhibited stronger absorption in the visible region (λ > 420 nm). ,− ,− In general, these PSs are more stable and give higher product yields. For instance, photocatalytic conversion of CO 2 to CO was reported using 9-cyanoanthracene ( 13 ) as the PS and [Fe­(dhTPP)­Cl] + (dhTPP = 5,10,15,20-tetrakis­(2′,6′-dihydroxyphenyl)­porphyrin) as the catalyst in acetonitrile containing TEA as the sacrificial donor .…”

“…A few of the organic PSs previously used in the photocatalytic H 2 generation were also studied in photocatalytic reduction of CO 2 . − Interestingly, these catalytic systems exhibited activities comparable to those demonstrated by metal chromophores. , For example, Eosin Y ( 1a ) was reported to efficiently promote the CO 2 photoreduction with the mononuclear nickel catalysts Ni­(pbt)­(pyS) 2 and Ni­(pbi)­(pyS) 2 (pbi = pyridylbenzimidazole, pbt = pyridylbenzothiazole, and pyS = pyridine-2- thiolate) in pH 10.7 ethanol/H 2 O (1:1) containing TEOA . HCOO – was obtained selectively (ca.…”

“…In addition, the organic dye TADF 10b , which was previously used as a PS for photocatalytic H 2 generation, was also studied in the photocatalytic CO 2 reduction using the iron mono terpyridine catalyst Fe­(ttpy)­Cl 3 (ttpy = 4′-(p-tolyl)-2,2′:6′,2″-terpyridine) and the bis- terpyridine catalyst [Fe­(Rtpy) 2 ] 2+ (Rtpy = 4-substituted 2,2′:6′,2″-terpyridine and R = NMe 2 , Cl and H). , The photocatalytic CO 2 reduction with 10b /Fe­(ttpy)­Cl 3 was performed in DMF with TEA as the sacrificial donor, and CO was obtained with selectivity greater than 99% and TON of 244 (vs cat). The CO yield (TON = 17) was lower using [Ru­(bpy) 3 ] 2+ as the PS, while no CO was obtained with the xanthene dyes 1a and 1d .…”

“…2780 and 4500) was obtained with the catalysts bearing R = Cl and H, respectively. 104 In comparison, much less CO was produced (TON = 19) when the same amount of [Ru(bpy) 3 ] 2+ was used as PS or when the reaction was performed in acetonitrile (TON = 992).…”