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Title: Evaluation of the coordination preferences and catalytic pathways of heteroaxial cobalt oximes towards hydrogen generation

Abstract

Three new heteroaxial cobalt oxime catalysts, namely [Co III(prdioxH)( 4tBupy)(Cl)]PF 6 (1), [Co III(prdioxH)( 4Pyrpy)(Cl)]PF 6 (2), and [Co III(prdioxH)( 4Bzpy)(Cl)]PF 6 (3) have been studied. These species contain chloro and substituted tert-butyl/pyrrolidine/benzoyl-pyridino ligands axially coordinated to a trivalent cobalt ion bound to the N 4-oxime macrocycle (2 E,2' E,3 E,3' E)-3,3'-(propane-1,3-diylbis(azanylylidene))bis(butan-2-one)dioxime, abbreviated (prdioxH)– in its monoprotonated form. Emphasis was given to the spectroscopic investigation of the coordination preferences and spin configurations among the different 3d 6 Co III, 3d 7 Co II, and 3d 8 Co I oxidation states of the metal, and to the catalytic proton reduction with an evaluation of the pathways for the generation of H 2 via Co III–H or Co II–H intermediates by mono and bimetallic routes. The strong field imposed by the (prdioxH)– ligand precludes the existence of high-spin configurations, and 6-coordinate geometry is favored by the LSCo III species. Species 1 and 3 show a split Co III/Co II electrochemical wave associated with partial chemical conversion to a [Co III(prdioxH)Cl 2] species, whereas 2 shows a single event. The reduction of these Co III complexes yields LSCo II and LSCo I species in which the pyridine acts as the dominantmore » axial ligand. In the presence of protons, the catalytically active Co I species generates a Co III–H hydride species that reacts heterolytically with another proton to generate dihydrogen. The intermediacy of a trifluoroacetate-bound Co III/Co II couple in the catalytic mechanism is proposed. Finally, these results allow for a generalization of the behavior of heteroaxial cobalt macrocycles and serve as guidelines for the development of new catalysts based on macrocyclic frameworks.« less

Authors:
 [1];  [1];  [2];  [1];  [1];  [1];  [3];  [2];  [1];  [1]
  1. Wayne State Univ., Detroit, MI (United States)
  2. Argonne National Lab. (ANL), Argonne, IL (United States)
  3. Michigan State Univ., East Lansing, MI (United States)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); Chemical Sciences; Geosciences; and Biosciences Division
OSTI Identifier:
1351546
Grant/Contract Number:  
AC02-06CH11357
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Chemical Science
Additional Journal Information:
Journal Volume: 7; Journal Issue: 5; Journal ID: ISSN 2041-6520
Publisher:
Royal Society of Chemistry
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Basu, Debashis, Mazumder, Shivnath, Niklas, Jens, Baydoun, Habib, Wanniarachchi, Dakshika, Shi, Xuetao, Staples, Richard J., Poluektov, Oleg, Schlegel, H. Bernhard, and Verani, Cláudio N. Evaluation of the coordination preferences and catalytic pathways of heteroaxial cobalt oximes towards hydrogen generation. United States: N. p., 2016. Web. doi:10.1039/c5sc04214c.
Basu, Debashis, Mazumder, Shivnath, Niklas, Jens, Baydoun, Habib, Wanniarachchi, Dakshika, Shi, Xuetao, Staples, Richard J., Poluektov, Oleg, Schlegel, H. Bernhard, & Verani, Cláudio N. Evaluation of the coordination preferences and catalytic pathways of heteroaxial cobalt oximes towards hydrogen generation. United States. doi:10.1039/c5sc04214c.
Basu, Debashis, Mazumder, Shivnath, Niklas, Jens, Baydoun, Habib, Wanniarachchi, Dakshika, Shi, Xuetao, Staples, Richard J., Poluektov, Oleg, Schlegel, H. Bernhard, and Verani, Cláudio N. Tue . "Evaluation of the coordination preferences and catalytic pathways of heteroaxial cobalt oximes towards hydrogen generation". United States. doi:10.1039/c5sc04214c. https://www.osti.gov/servlets/purl/1351546.
@article{osti_1351546,
title = {Evaluation of the coordination preferences and catalytic pathways of heteroaxial cobalt oximes towards hydrogen generation},
author = {Basu, Debashis and Mazumder, Shivnath and Niklas, Jens and Baydoun, Habib and Wanniarachchi, Dakshika and Shi, Xuetao and Staples, Richard J. and Poluektov, Oleg and Schlegel, H. Bernhard and Verani, Cláudio N.},
abstractNote = {Three new heteroaxial cobalt oxime catalysts, namely [CoIII(prdioxH)(4tBupy)(Cl)]PF6 (1), [CoIII(prdioxH)(4Pyrpy)(Cl)]PF6 (2), and [CoIII(prdioxH)(4Bzpy)(Cl)]PF6 (3) have been studied. These species contain chloro and substituted tert-butyl/pyrrolidine/benzoyl-pyridino ligands axially coordinated to a trivalent cobalt ion bound to the N4-oxime macrocycle (2E,2'E,3E,3'E)-3,3'-(propane-1,3-diylbis(azanylylidene))bis(butan-2-one)dioxime, abbreviated (prdioxH)– in its monoprotonated form. Emphasis was given to the spectroscopic investigation of the coordination preferences and spin configurations among the different 3d6 CoIII, 3d7 CoII, and 3d8 CoI oxidation states of the metal, and to the catalytic proton reduction with an evaluation of the pathways for the generation of H2via CoIII–H– or CoII–H– intermediates by mono and bimetallic routes. The strong field imposed by the (prdioxH)– ligand precludes the existence of high-spin configurations, and 6-coordinate geometry is favored by the LSCoIII species. Species 1 and 3 show a split CoIII/CoII electrochemical wave associated with partial chemical conversion to a [CoIII(prdioxH)Cl2] species, whereas 2 shows a single event. The reduction of these CoIII complexes yields LSCoII and LSCoI species in which the pyridine acts as the dominant axial ligand. In the presence of protons, the catalytically active CoI species generates a CoIII–H– hydride species that reacts heterolytically with another proton to generate dihydrogen. The intermediacy of a trifluoroacetate-bound CoIII/CoII couple in the catalytic mechanism is proposed. Finally, these results allow for a generalization of the behavior of heteroaxial cobalt macrocycles and serve as guidelines for the development of new catalysts based on macrocyclic frameworks.},
doi = {10.1039/c5sc04214c},
journal = {Chemical Science},
number = 5,
volume = 7,
place = {United States},
year = {Tue Feb 02 00:00:00 EST 2016},
month = {Tue Feb 02 00:00:00 EST 2016}
}

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