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Electrocatalytic Proton Reduction by a Cobalt Complex Containing a Proton-Responsive Bis(alkylimdazole)methane
Pradip Ghosh1,2, Sander de Vos1, Martin Lutz3
1Organic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG, Utrecht, The Netherlands.
Abstract:
Homogeneous electrocatalytic proton reduction is reported using cobalt complex [1](BF4 )2 . This complex comprises two bis(1-methyl-4,5-diphenyl-1H-imidazol-2-yl)methane (HBMIM ) ligands that contain an acidic methylene moiety in their backbone. Upon reduction of [1](BF4 )2 by either electrochemical or chemical means, one of its HBMIM ligands undergoes deprotonation under the formation of dihydrogen. Addition of a mild proton source (acetic acid) to deprotonated complex [2](BF4 ) regenerates protonated complex [1](BF4 )2 . In presence of acetic acid in acetonitrile solvent [1](BF4 )2 shows electrocatalytic proton reduction with a kobs 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 HBMIM ligand and a CoII -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.
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