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

Homogeneous electrocatalytic proton reduction is reported using cobalt complex [1](BF(4))(2). This complex comprises two bis(1‐methyl‐4,5‐diphenyl‐1H‐imidazol‐2‐yl)methane (HBMIM [Formula: see text] ) 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 HBMIM [Formula: see text] ligands 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 HBMIM [Formula: see text] ligand 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.