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Title: X-ray Absorption Spectroscopy and Theoretical Investigation of the Reductive Protonation of Cyclopentadienyl Cobalt Compounds

Abstract

Cobalt(III) hydrides, formed via protonation of basic cobalt(I) centers, have long been recognized as key intermediates in the electrocatalytic reduction of protons to hydrogen. An understanding of the structural and electronic factors that govern their formation is key to developing more efficient and potent catalysts. A combination of Co K-edge X-ray absorption spectroscopy, extended X-ray absorption fine structure, density functional theory (DFT), and time-dependent DFT methods have been used to investigate several cyclopentadienyl (Cp) Co(III)L (L = ligand) species and their two-electron reduced Co(I) analogues. The results reveal that when L is strongly π-accepting, the reduced species demonstrates strong backbonding between the electron-rich Co(I) center and the ligand L, resulting in a weakly basic Co center that does not protonate to form a Co(III)–H. In contrast, a weakly π-accepting or σ-donating ligand system results in an electron-rich Co(I) center, which is readily protonated to form a Co(III)–H. Here, this study reveals the strength of a combined X-ray spectroscopy/theory method in understanding the role of ligands in tuning the electronic structure and subsequent reactivity of the metal center.

Authors:
ORCiD logo [1];  [2]; ORCiD logo [1]; ORCiD logo [3]
  1. Stanford Univ., CA (United States). Dept. of Chemistry
  2. Stanford Univ., CA (United States). Dept. of Chemistry; SLAC National Accelerator Lab., Menlo Park, CA (United States). Stanford Synchrotron Radiation Lightsource (SSRL)
  3. SLAC National Accelerator Lab., Menlo Park, CA (United States). Stanford Synchrotron Radiation Lightsource (SSRL)
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23); National Science Foundation (NSF); National Institutes of Health (NIH)
OSTI Identifier:
1503552
Grant/Contract Number:  
AC02-76SF00515; CHE-1565947
Resource Type:
Accepted Manuscript
Journal Name:
Inorganic Chemistry
Additional Journal Information:
Journal Volume: 58; Journal Issue: 2; 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; 36 MATERIALS SCIENCE

Citation Formats

McLoughlin, Elizabeth A., Giles, Logan J., Waymouth, Robert M., and Sarangi, Ritimukta. X-ray Absorption Spectroscopy and Theoretical Investigation of the Reductive Protonation of Cyclopentadienyl Cobalt Compounds. United States: N. p., 2019. Web. doi:10.1021/acs.inorgchem.8b02475.
McLoughlin, Elizabeth A., Giles, Logan J., Waymouth, Robert M., & Sarangi, Ritimukta. X-ray Absorption Spectroscopy and Theoretical Investigation of the Reductive Protonation of Cyclopentadienyl Cobalt Compounds. United States. doi:10.1021/acs.inorgchem.8b02475.
McLoughlin, Elizabeth A., Giles, Logan J., Waymouth, Robert M., and Sarangi, Ritimukta. Fri . "X-ray Absorption Spectroscopy and Theoretical Investigation of the Reductive Protonation of Cyclopentadienyl Cobalt Compounds". United States. doi:10.1021/acs.inorgchem.8b02475. https://www.osti.gov/servlets/purl/1503552.
@article{osti_1503552,
title = {X-ray Absorption Spectroscopy and Theoretical Investigation of the Reductive Protonation of Cyclopentadienyl Cobalt Compounds},
author = {McLoughlin, Elizabeth A. and Giles, Logan J. and Waymouth, Robert M. and Sarangi, Ritimukta},
abstractNote = {Cobalt(III) hydrides, formed via protonation of basic cobalt(I) centers, have long been recognized as key intermediates in the electrocatalytic reduction of protons to hydrogen. An understanding of the structural and electronic factors that govern their formation is key to developing more efficient and potent catalysts. A combination of Co K-edge X-ray absorption spectroscopy, extended X-ray absorption fine structure, density functional theory (DFT), and time-dependent DFT methods have been used to investigate several cyclopentadienyl (Cp) Co(III)L (L = ligand) species and their two-electron reduced Co(I) analogues. The results reveal that when L is strongly π-accepting, the reduced species demonstrates strong backbonding between the electron-rich Co(I) center and the ligand L, resulting in a weakly basic Co center that does not protonate to form a Co(III)–H. In contrast, a weakly π-accepting or σ-donating ligand system results in an electron-rich Co(I) center, which is readily protonated to form a Co(III)–H. Here, this study reveals the strength of a combined X-ray spectroscopy/theory method in understanding the role of ligands in tuning the electronic structure and subsequent reactivity of the metal center.},
doi = {10.1021/acs.inorgchem.8b02475},
journal = {Inorganic Chemistry},
number = 2,
volume = 58,
place = {United States},
year = {2019},
month = {1}
}

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Works referencing / citing this record:

CCDC 1866349: Experimental Crystal Structure Determination
dataset, January 2019

  • McLoughlin, Elizabeth A.; Giles, Logan J.; Waymouth, Robert M.
  • Cambridge Crystallographic Data Centre
  • DOI: 10.5517/ccdc.csd.cc20n2tl

CCDC 1866350: Experimental Crystal Structure Determination
dataset, January 2019

  • McLoughlin, Elizabeth A.; Giles, Logan J.; Waymouth, Robert M.
  • Cambridge Crystallographic Data Centre
  • DOI: 10.5517/ccdc.csd.cc20n2vm