Visible‐Light Photocatalytic Reduction of CO₂ to Formic Acid with a Ru Catalyst Supported by N,N′‐Bis(diphenylphosphino)‐2,6‐diaminopyridine Ligands

Abstract

Visible-light photocatalytic CO 2 reduction is carried out by using aR u II complex supportedb yN,N'-bis(diphenylphosphino)-2,6-diaminopyridine( "PNP")l igands, an unprecedented molecular architecture for this reaction that breaks the longstanding domination of a-diimine ligands. These competent catalysts transform CO 2 into formic acid with high selectivity and turnover number.Aproposed mechanism, with combined electron transfer and catalytic cycles, models the experimental rate of formic acid production.Designing and assembling catalysts that can utilize the energy of visible light to overcome the barriers to reduce CO 2 is an important fundamentala nd technological challenge. Success in this endeavor requires confronting the inherent stabilitya nd low thermodynamic value of CO 2 and would transform this ubiquitous waste product into av aluable feedstock. For example, photocatalytic formation of formic acid, at wo-electron reductionp roduct of CO 2 ,w ould yield ac ommodity chemical and al iquid fuel. Furthermore, formic acid has been identified and explored as ap otential carrier of dihydrogen. [1,2] Homogeneous catalysts have been developed for CO 2 reduction under both electrochemical and photochemical conditions. [3][4][5][6] Photocatalysis is ap articularly appealing approacha s it relies on an essentially limitless and clean solar energy source.P hotocatalytic systemsc onsisto fi ntegrated components that include ap hotosensitizer (PS)f or harvesting the energy of the light, an electron donor (ED)t hat provides electrons for the reduction, and ac atalyst (CAT)t hat is as ite for the transformation of CO 2 .T oo ur knowledge,s ince their discovery in 1985, [7] all of the reported molecular photocatalysts based on Ru II have used a-diimine supporting ligandsa nd these speciesh ave fallen into two broad groups.O ne class are bis(a-diimine) speciesr epresentedb ycis-[Ru(N^N) 2 (CO) 2 ] 2 + [8][9][10][11] and the other are mono(a-diimine) catalysts represented by cis,trans-[Ru(N^N)(CO) 2 Cl 2 ]. [12][13][14] Althoughavariety of substituents on the a-diimine ligands have been productively explored to improvec atalystp erformance, given the maturity of this field, ab roader variationo fm olecular architecture is required to provide new insights and stimulate new concepts in this field. Ligand variation and discoverya re ac entral challenge in catalysis and expanding Ru-based photocatalysts beyond the restrictions of a-diimine support is certainly warranted. Support for this approachc omes from av ery recent report on the use of ap hotocatalytic phosphine-substituted Ru II terpyridine complex-trans-[Ru(tpy)(8-quinolyl(diphenyl)phosphine)-(MeCN)] 2 + -that functions as both ap hotosensitizer andacatalyst for CO 2 reduction. [15,16] Recently,p incer ligand-supported catalysts of Fe, Co, Ru, and Ir have been shown to have excellent activity and selectivity for hydrogenation of CO 2 . [17][18][19][20][21][22][23] Pincer-supported ruthenium complexes can catalyze hydrogenation of CO 2 to yield formate, as wella st he ...

Formic Acid Generation from CO2 Reduction by MOF-253 Coordinated Transition Metal Complexes: A Computational Chemistry Perspective

“…The energetics of possible intermediates during the reduction mechanism process were optimized with the hybrid B3LYP functional [20][21][22], in which elements H, C, N, and O were described by basis set of 6-31 g with diffuse functions [23], with the addition of a polarized function [24] to the heavy atoms. This hybrid function has been commonly adopted for theoretical characterizations of the formic acid generation mechanism by organometallic complexes [25][26][27][28][29][30][31][32] The transition metals were described by triple-zeta quality LANL2TZ pseudopotential basis set except Hf [33]. The van der Waals interactions were taken into account using the D3 version of Grimme's dispersion with Becke-Johnson damping [34,35].…”

Towards Sustainable Oxalic Acid from CO2and Biomass

“…Hence, the most common systems for this process are homogeneous catalysts, which have been first used by Tanaka and co‐workers in the 1980s [228] . In recent years this topic gained new interest and many new systems were studied and developed [224,229–235] . The selectivity of the homogeneous systems depends on a myriad of parameters in the process design including the solvent for CO 2 solubilization, electron and proton sources, photosensitizers for light‐harvesting, and lastly the design of the catalysts itself [224] .…”

Photochemical reduction of carbon dioxide to formic acid

“…Similar results were obtained, however a slightly lower efficiency was observed. 49 In 2020, Arikawa et al used CNC pincer complexes since they were known to incorporate CO 2 . 50 In their experiment, CO 2 was reduced in the presence of the CNC Ru catalyst [Ru (dmb) 3 ](PF 6 ) 2 (23) (dmb = 4,4′-dimethylbipyridine) as a photosensitizer, BI(OH)H as the sacrificial electron donor and DMA/ TEOA as the solvent mixture.…”