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Title: Push or Pull? Proton Responsive Ligand Effects in Rhenium Tricarbonyl CO 2 Reduction Catalysts

Proton responsive ligands offer control of catalytic reactions through modulation of pH-dependent properties, second coordination sphere stabilization of transition states, or by providing a local proton source for multi-proton, multi-electron reactions. Two fac-[ReI(α-diimine)(CO)₃Cl] complexes with α-diimine = 4,4'- (or 6,6'-) dihydroxy-2,2'-bipyridine (4DHBP and 6DHBP) have been prepared and analyzed as electrocatalysts for reduction of carbon dioxide. Consecutive electrochemical reduction of these complexes yields species identical to those obtained by chemical deprotonation. An energetically feasible mechanism for reductive deprotonation is proposed in which the bpy anion is protonated followed by loss of H₂ and 2H⁺. Cyclic voltammetry reveals a two-electron, three-wave system owing to competing EEC and ECE pathways. The chemical step of the ECE pathway might be attributed to the reductive deprotonation. but cannot be distinguished from chloride dissociation. The rate obtained by digital simulation is approximately 8 s⁻¹. Under CO₂, these competing reactions generate a two-slope catalytic waveform with onset potential of –1.65 V vs Ag/AgCl. Reduction of CO₂ to CO by the [ReI (4DHBP–2H⁺)(CO)₃]⁻ suggests the interaction of CO₂ with the deprotonated species or a third reduction followed by catalysis. Conversely, the reduced form of [Re(6DHBP)(CO)₃Cl] converts CO₂ to CO with a single turnover.
Authors:
 [1] ;  [1] ;  [2] ;  [3] ;  [1]
  1. Brookhaven National Lab. (BNL), Upton, NY (United States). Dept. of Chemistry
  2. Brookhaven National Lab. (BNL), Upton, NY (United States). Dept. of Chemistry; City Univ. (CUNY), NY (United States). Buruch College. Dept. of Natural Science
  3. National Inst. of Advanced Industrial Science and Technology (AIST), Tsukuba (Japan); Japan Science and Technology Agency (JST), Saitama (Japan)
Publication Date:
OSTI Identifier:
1182537
Report Number(s):
BNL--107638-2015-JA
Journal ID: ISSN 1520-6106; R&D Project: CO026; KC0304030
Grant/Contract Number:
SC00112704
Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry
Additional Journal Information:
Journal Volume: 119; Journal Issue: 24; Journal ID: ISSN 1520-6106
Publisher:
American Chemical Society
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY Proton responsive ligands; chemical deprotonation; chloride dissociation; catalytic reactions