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Combined Spectroscopic and Electrochemical Detection of a Ni I ⋅⋅⋅HN Bonding Interaction with Relevance to Electrocatalytic H 2 Production
Author(s) -
Kochem Amélie,
O'Hagan Molly,
Wiedner Eric S.,
van Gastel Maurice
Publication year - 2015
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201500954
Subject(s) - electrochemistry , production (economics) , relevance (law) , chemistry , analytical chemistry (journal) , materials science , electrode , organic chemistry , political science , law , economics , macroeconomics
The [Ni(P R 2 N R′ 2 ) 2 ] 2+ family of complexes are exceptionally active catalysts for proton reduction to H 2 . In this manuscript, we explore the first protonation step of the proposed catalytic cycle by using a catalytically inactive Ni I complex possessing a sterically demanding variation of the ligand. Due to the paramagnetic nature of the Ni I oxidation state, the protonated Ni I intermediate has been characterized through a combination of cyclic voltammetry, electron nuclear double resonance (ENDOR) spectroscopy, and hyperfine sublevel correlation (HYSCORE) spectroscopy. Both the electrochemical and spectroscopic studies indicate that the Ni I complex is protonated at a pendant amine that is endo to Ni, which suggests the presence of an intramolecular Ni I ⋅⋅⋅ HN bonding interaction. Using density functional theory, the hydrogen bond was found to involve three doubly‐occupied, localized molecular orbitals: the 3d xz , 3d z 2, and 3d yz orbitals of nickel. These studies provide the first direct experimental evidence for this critical catalytic intermediate, and implications for catalytic H 2 production are discussed.