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Title: Ligand Noninnocence in Nickel Porphyrins: Nickel Isobacteriochlorin Formation under Hydrogen Evolution Conditions

Abstract

Here, an electron-deficient nickel porphyrin complex undergoes facile ring reduction to form a nickel isobacteriochlorin complex under hydrogen evolution conditions. Spectroscopic experiments indicate that the reduced nickel porphyrin undergoes subsequent reduction and protonation to form a phlorin anion rather than a metal hydride, demonstrating that the key initial proton-coupled electron transfer step is directed toward the ligand versus the metal. The phlorin anion facilely converts to the isobacteriochlorin in the presence of two-electron and three-proton equivalents. Cyclic voltammetry (CV) and spectroscopic experiments reveal that the four-electron, four-proton electrochemical reduction of nickel porphyrin to isobacteriochlorin occurs promptly in the presence of the strong proton donor tosic acid, followed by hydrogen evolution reaction (HER) catalysis at slightly more negative potentials. CVs of independently synthesized Ni isobacteriochlorin show a catalytic HER at the same potentials as those observed for the HER in CVs of the Ni porphyrin. We discover that, under strongly acidic conditions, the HER catalysis arises from conversion of the Ni isobacteriochlorin into a nickel-containing, catalytically active electrode-adsorbed species. These results show that Ni porphyrin converts to Ni isobacteriochlorin under HER catalysis conditions via a ligand-based PCET process and that it is the isobacteriochlorin complex which gives rise to an activemore » HER catalysis.« less

Authors:
 [1];  [1]; ORCiD logo [1]
  1. Harvard Univ., Cambridge, MA (United States)
Publication Date:
Research Org.:
Harvard Univ., Cambridge, MA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division
OSTI Identifier:
1597839
Grant/Contract Number:  
SC0017619
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Inorganic Chemistry
Additional Journal Information:
Journal Volume: 58; Journal Issue: 12; Journal ID: ISSN 0020-1669
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Maher, Andrew G., Liu, Mengran, and Nocera, Daniel G. Ligand Noninnocence in Nickel Porphyrins: Nickel Isobacteriochlorin Formation under Hydrogen Evolution Conditions. United States: N. p., 2019. Web. doi:10.1021/acs.inorgchem.9b00717.
Maher, Andrew G., Liu, Mengran, & Nocera, Daniel G. Ligand Noninnocence in Nickel Porphyrins: Nickel Isobacteriochlorin Formation under Hydrogen Evolution Conditions. United States. https://doi.org/10.1021/acs.inorgchem.9b00717
Maher, Andrew G., Liu, Mengran, and Nocera, Daniel G. Thu . "Ligand Noninnocence in Nickel Porphyrins: Nickel Isobacteriochlorin Formation under Hydrogen Evolution Conditions". United States. https://doi.org/10.1021/acs.inorgchem.9b00717. https://www.osti.gov/servlets/purl/1597839.
@article{osti_1597839,
title = {Ligand Noninnocence in Nickel Porphyrins: Nickel Isobacteriochlorin Formation under Hydrogen Evolution Conditions},
author = {Maher, Andrew G. and Liu, Mengran and Nocera, Daniel G.},
abstractNote = {Here, an electron-deficient nickel porphyrin complex undergoes facile ring reduction to form a nickel isobacteriochlorin complex under hydrogen evolution conditions. Spectroscopic experiments indicate that the reduced nickel porphyrin undergoes subsequent reduction and protonation to form a phlorin anion rather than a metal hydride, demonstrating that the key initial proton-coupled electron transfer step is directed toward the ligand versus the metal. The phlorin anion facilely converts to the isobacteriochlorin in the presence of two-electron and three-proton equivalents. Cyclic voltammetry (CV) and spectroscopic experiments reveal that the four-electron, four-proton electrochemical reduction of nickel porphyrin to isobacteriochlorin occurs promptly in the presence of the strong proton donor tosic acid, followed by hydrogen evolution reaction (HER) catalysis at slightly more negative potentials. CVs of independently synthesized Ni isobacteriochlorin show a catalytic HER at the same potentials as those observed for the HER in CVs of the Ni porphyrin. We discover that, under strongly acidic conditions, the HER catalysis arises from conversion of the Ni isobacteriochlorin into a nickel-containing, catalytically active electrode-adsorbed species. These results show that Ni porphyrin converts to Ni isobacteriochlorin under HER catalysis conditions via a ligand-based PCET process and that it is the isobacteriochlorin complex which gives rise to an active HER catalysis.},
doi = {10.1021/acs.inorgchem.9b00717},
url = {https://www.osti.gov/biblio/1597839}, journal = {Inorganic Chemistry},
issn = {0020-1669},
number = 12,
volume = 58,
place = {United States},
year = {2019},
month = {5}
}

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Works referencing / citing this record:

Boosting hydrogen evolution by using covalent frameworks of fluorinated cobalt porphyrins supported on carbon nanotubes
journal, January 2019