Tuning of Ionic Second Coordination Sphere in Evolved Rhenium Catalyst for Efficient Visible‐Light‐Driven CO₂ Reduction

Abstract

DedicatedtoProfessor Mingyuan He on the occasion of his 80th birthday. Developing an efficient and easy-to-handle strategy in designing catalysts for CO 2 reduction into CO by harnessing sunlight is ap romising project. Here, af acile strategy was developed to design aR ec atalyst modified with an ionic secondaryc oordination sphere for photoreduction of CO 2 to CO by visible light. By adding ionic liquids or tuning ad ifferent ionic secondary coordination sphere, it was discovered that an outstanding optical property,o ther than CO 2 absorption ability or the ability to dissociation of chloride anion,i st he prerequisite for catalyst design.A ccordingly,an ovel Re catalyst, {Re[BpyMe(tris(2-hydroxyethyl)amine)](CO) 3 Cl}Br (Re-THEA), was designed, screened, and resulted in ar elative high quantum yield (up to 34 %) for visible-light-induced CO 2 reduction with as ingle-molecule system.D FT calculations, combined with experimental outcomes, suggested the pendant ionic tris(2-hydroxyethyl)amino (THEA) group on Re-THEA can enhance visible-light absorption, stabilize reaction intermediates, and suppress the Re-Re dimer formation. The increasing concentration of CO 2 in the atmosphere has caused plentyo fc limatei ssues and attracted increasing interest among governments and scientists. [1] Conversion of CO 2 into valuablep roducts, or even into fuels, is an appealing access strategy to relieve energy shortages and realize carbon cycling. [2] However,f urthere nergy input is necessary in most CO 2 conversionsb ecause of the high thermodynamic and kinetic stability of CO 2. [3] One attractive approacht oa ddress this problem is to apply sunlight, aclean, renewable, and abundant energy source, for the reduction of CO 2 to CO because CO can be easily transformed into liquid fuels throughF ischer-Tropsch synthesis. [4] Photocatalytic CO 2 reduction reaction(CO 2 RR) is a proton-coupled electron-transfer (PCET) process and typically accomplished by as ystem composed of three parts:p hotosen-[a] Dr.

Pendent trifluoroethanol reveals solvation dependent mechanisms of electrocatalytic CO2 reduction by rhenium(I) bipyridine fac-tricarbonyl

“…This ECE mechanism may be due to the alcohol facilitating the partial dissociation of the axial chloride upon 1 ereduction of the complex. 20,21,26,29,45,46 The observation of dimer formation following the first reduction of 2 supports this assignment. The chemical step following the first electrochemical reduction may also be attributable to reductive deprotonation of the alcohol that would result in loss of the chloride from the resulting dianionic species.…”

“…The second reduction of 2 is observed at 120 mV more positive than 3 and displays attenuated current indicative of an ECE process associated with the first reduction likely involving loss of the chloride ligand or perhaps reductive deprotonation of the alcohol. 20,21,26,29,32,33,[45][46][47] 2 displays additional cathodic features at -2.14 V and -2.34 V vs. Fc +/0 , the second of which is attributed to a second reduction of the bipyridine ligand. 12,14,40 Exchange of chloride for MeCN in 1-OTf and 2-OTf results in an anodic shift of the first reduction.…”

“…11,16 A number of groups have explored the effect of pendent proton donors and hydrogen-bond acceptors on the catalytic activity of these catalysts. [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] However, there have been only a few reports which provide experimental evidence for the protonation-first pathway. 19,24,29,35 In particular, the report by Rochford and coworkers detailed the electrocatalytic activity of a manganese catalyst employing a modified bipyridine ligand containing four pendent orthomethoxy phenyl groups at the 6, 6ʹ positions.…”

Ionic Liquid-Modified Porous Organometallic Polymers as Efficient and Selective Photocatalysts for Visible-Light-Driven CO 2 Reduction

“…For CO 2 photoreduction to CO, rhenium complexes of fac -[Re I (N^N)(CO) 3 X] (N^N=diimine, X=Cl, Br) as photocatalysts have gained long-term attention because of their excellent performance [ 8 – 16 ]. However, the notorious instability of fac -[Re I (N^N)(CO) 3 X] deriving form bimetallic decomposition greatly limits their application.…”

“…For facilitated CO 2 absorption, IL has been directly added into the photocatalytic CO 2 systems, which are proven to accelerate the process of CO 2 to CO conversion and inhibits H 2 generation [ 34 , 35 ]. In addition, the ionic group on the second coordination sphere, i.e., ionic second coordination sphere, has been proven to be promoting CO 2 photoreduction [ 16 ]. Therefore, we speculate ILs as regulators that can be covalently introduced into porous materials to enhance their photocatalytic performance.…”