skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Proton-Coupled, Low-Energy Pathway for Electrocatalytic CO 2 Reduction at Re(Diimine) Complexes with a Conjugated Pyrazinyl Moiety
Title: Proton-Coupled, Low-Energy Pathway for Electrocatalytic CO 2 Reduction at Re(Diimine) Complexes with a Conjugated Pyrazinyl Moiety
Large conjugated carbon framework has been incorporated as the diimine ligand for Re(α-diimine)(CO)3Cl complexes with a pyrazinyl linkage, either to increase energy efficiency or to turn them into heterogeneous catalysts for selective electrocatalytic CO2 reduction. However, there exists a nonmonotonic dependence of CO2 reduction overpotential on the conjugation size of the ligands. Understanding its origin could facilitate heterogenization of molecular catalysts with improved energy efficiency. Here, we show that the conjugated pyrazinyl moiety plays a crucial role in catalysis by enabling a proton-coupled, lower-energy pathway for CO2 reduction. With ligands of moderate size, the pathway leads to previously unknown intermediates and decreases CO2 reduction overpotential. Because the pathway hinges on the basicity of the pyrazinyl nitrogen, we propose that it imposes a limit on the conjugation size of the ligand for the pathway to be effective.  more » « less
Award ID(s):
1764264
PAR ID:
10376894
Author(s) / Creator(s):
; ; ; ; ;
Date Published:
Journal Name:
Inorganic Chemistry
ISSN:
0020-1669
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; (, Dalton Transactions)
    Heterogenized molecular catalysts have shown interesting activities in different chemical transformations. In our previous studies, a molecular catalyst, Re(bpy)(CO)3Cl where bpy is 2,2’-bipyridine, was covalently attached to silica surfaces via an amide linkage for use in photocatalytic CO2 reduction. Derivatizing the bpy ligand with electron-withdrawing amide groups led to detrimental effects on the catalytic activity of Re(bpy)(CO)3Cl. In this study, an alkyl amine linkage is utilized to attach Re(bpy)(CO)3Cl onto SiO2 in order to eliminate the detrimental effects of the amide linkage by breaking the conjugation between the bpy ligand and the amide group. However, the heterogenized Re(I) catalyst containing the alkyl amine linkage demonstrates even lower activity than the one containing the amide linkage in photocatalytic CO2 reduction. Infrared studies suggest that the presence of the basic amine group led to the formation of a photocatalytically inactive Re(I)-OH species on SiO2. Furthermore, the amine group likely contributes to the stabilization of a surface Re(I)-carboxylato species formed upon light irradiation, resulting in the low activity of the heterogenized Re(I) catalyst containing the alkyl amine linkage. 
    more » « less
  2. ; ; ; ; ; ; ; ; (, European Journal of Inorganic Chemistry)
    Abstract A new method to synthesize complexes of the type [(CNC)RuII(NN)L]n+has been introduced, where CNC is a tridentate pincer composed of two (benz)imidazole derived NHC rings and a pyridyl ring, NN is a bidentate aromatic diimine ligand, L=bromide or acetonitrile, and n=1 or 2. Following this new method a series of six new complexes has been synthesized and characterized by spectroscopic, analytic, crystallographic, and computational methods. Their electrochemical properties have been studiedviacyclic voltammetry under both N2and CO2atmospheres. Photocatalytic reduction of CO2to CO was performed using these complexes both in the presence (sensitized) and absence (self‐sensitized) of an external photosensitizer. This study evaluates the effect of different CNC, NN, and L ligands in sensitized and self‐sensitized photocatalysis. Catalysts bearing the benzimidazole derived CNC pincer show much better activity for both sensitized and self‐sensitized photocatalysis as compared to catalysts bearing the imidazole derived CNC pincer. Furthermore, self‐sensitized photocatalysis requires a diimine ligand for CO2reduction with catalyst2ACNbeing the most active catalyst in this series with TON=85 and TOF=22 h−1with an electron donating 4,4′‐dimethyl‐2,2′‐bipyridyl (dmb) ligand and a benzimidazole derived CNC pincer. 
    more » « less
  3. ; ; ; ; ; ; (, ChemCatChem)
    Abstract The reduction of dioxygen to produce selectively H2O2or H2O is crucial in various fields. While platinum‐based materials excel in 4H+/4e−oxygen reduction reaction (ORR) catalysis, cost and resource limitations drive the search for cost‐effective and abundant transition metal catalysts. It is thus of great importance to understand how the selectivity and efficiency of 3d‐metal ORR catalysts can be tuned. In this context, we report on a Co complex supported by a bisthiolate N2S2‐donor ligand acting as a homogeneous ORR catalyst in acetonitrile solutions both in the presence of a one‐electron reducing agent (selectivity for H2O of 93 % and TOFi=3 000 h−1) and under electrochemically‐assisted conditions (0.81 V <η<1.10 V, selectivity for H2O between 85 % and 95 %). Interestingly, such a predominant 4H+/4e−pathway for Co‐based ORR catalysts is rare, highlighting the key role of the thiolate donor ligand. Besides, the selectivity of this Co catalyst under chemical ORR conditions is inverse with respect to the Mn and Fe catalysts supported by the same ligand, which evidences the impact of the nature of the metal ion on the ORR selectivity. 
    more » « less
  4. ; ; ; ; (, Dalton Transactions)
    Dinuclear silver(I) complexes have recently gained attention for potential applications in visible light photochemistry. Our group has demonstrated that strong visible light absorption can occur in silver(I) dimers featuring redox-active naphthyridine diimine (NDI) ligands, resulting from a combination of close silver–silver interactions and low-lying ligand π* orbitals. A shortcoming of this previous work is that the sliver-NDI complexes displayed fluxional behavior due to rapid ligand exchange in solution; the ability to produce silver(I) dimers with targeted properties that maintain well-defined structures in solution remains an unmet challenge. Here, we describe the synthesis and characterization of a series of silver(I) dimers with naphthyridine-derived ligands, in which the ligand scaffold is systematically varied in order to determine structure/property relationships. We find that truncation of the NDI framework into an asymmetric “L-shaped” design results in a family of ligands that reliably produce structurally analogous silver(I) dimers. Ligands that maintain the π-conjugation of the iminopyridine motif consistently give silver(I) dimers with visible light absorption due to metal–metal to ligand charge transfer (MMLCT) transitions, and introduction of anionic (X-type) sites further increases stability in solution. 
    more » « less
  5. ; ; ; ; ; ; ; ; (, Journal of the American Chemical Society)
    The structural stability of nanocatalysts during electrochemical CO2 reduction (CO2RR) is crucial for practical applications. However, highly active nanocatalysts often reconstruct under reductive conditions, requiring stabilization strategies to maintain activity. Here, we demonstrate that the N-heterocyclic carbene (NHC) polymer stabilizes Au nanowire (NW) catalysts for selective CO2 reduction to CO over a broad potential range, enabling coupling with Cu NWs for one-step tandem conversion of CO2 to C2H4. By combining the hydrophobicity of the polystyrene chain and the strong binding of NHC to Au, the polymer stabilizes Au NWs and promotes CO2RR to CO with excellent selectivity (>90%) across −0.4 V to −1.0 V (vs RHE), a significantly broader range than unmodified Au NWs (−0.5 V to −0.7 V). Stable CO2RR at negative potentials yields a high jCO of 142 A/g Au at −1.0 V. In situ ATR-IR analysis indicates that the NHC polymer regulates the water microenvironment and suppresses hydrogen evolution at high overpotential. Moreover, NHC-Au NWs maintain excellent stability during 10 h of CO2RR testing, preserving the NW morphology and catalytic performance, while unmodified NWs degrade into nanoparticles with reduced activity and selectivity. NHC-Au NWs can be coupled with Cu NWs in a flow cell to catalyze CO2RR to C2H4 with 58% efficiency and a partial current density of 70 mA/cm2 (overall C2 product efficiency of 65%). This study presents an adaptable strategy to enhance the catalyst microenvironment, ensure stability, and enable efficient tandem CO2 conversion into value-added hydrocarbons. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email