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Electrocatalytic Proton Reduction by a Cobalt Complex Containing a Proton‐Responsive Bis(alkylimdazole)methane Ligand: Involvement of a C−H Bond in H 2 Formation
Author(s) -
Ghosh Pradip,
Vos Sander,
Lutz Martin,
Gloaguen Frederic,
Schollhammer Philippe,
Moret MarcEtienne,
Klein Gebbink Robertus J. M.
Publication year - 2020
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.201905746
Subject(s) - chemistry , deprotonation , heterolysis , protonation , ligand (biochemistry) , medicinal chemistry , intramolecular force , acetic acid , moiety , methylene , catalysis , acetonitrile , photochemistry , stereochemistry , organic chemistry , ion , biochemistry , receptor
Homogeneous electrocatalytic proton reduction is reported using cobalt complex [ 1 ](BF 4 ) 2 . This complex comprises two bis(1‐methyl‐4,5‐diphenyl‐1 H ‐imidazol‐2‐yl)methane (HBMIMPh2) ligands that contain an acidic methylene moiety in their backbone. Upon reduction of [ 1 ](BF 4 ) 2 by either electrochemical or chemical means, one of its HBMIMPh2ligands undergoes deprotonation under the formation of dihydrogen. Addition of a mild proton source (acetic acid) to deprotonated complex [ 2 ](BF 4 ) regenerates protonated complex [ 1 ](BF 4 ) 2 . In presence of acetic acid in acetonitrile solvent [ 1 ](BF 4 ) 2 shows electrocatalytic proton reduction with a k obs of ≈200 s −1 at an overpotential of 590 mV. Mechanistic investigations supported by DFT (BP86) suggest that dihydrogen formation takes place in an intramolecular fashion through the participation of a methylene C−H bond of the HBMIMPh2ligand and a Co II −H bond through formal heterolytic splitting of the latter. These findings are of interest to the development of responsive ligands for molecular (base)metal (electro)catalysis.