Inclusion of Peripheral Basic Groups Activates Dormant Cobalt-Based Molecular Complexes for Catalytic H2 Evolution in Water

The protein scaffold plays a key role during the enzymatic catalysis for metalloenzymes. Here we have rationally designed an enzyme-inspired outer coordination sphere in the form of protic functionalities, such as natural amino acid derived carboxylic acid and phenolic -OH groups, on the fringe of the cobalt-salen like complexes. This inclusion has enabled electrocatalytic H-2 evolution for an otherwise inactive cobalt-salen like core. The complexes containing peripheral carboxylic acid groups exhibited unique pH-switchable catalytic H-2 production that is connected with the pK(a) of the carboxylic acid group (similar to 4.0), suggesting the crucial involvement of the carboxylate group during the catalytic activity. The one- and two-dimensional NMR results of the complexes have indicated the presence of a possible hydrogen bonding network, generated by those protic groups in aqueous solution. These results highlight that an inactive metal complex can be activated for specific small molecule activation via rational inclusion of outer coordination sphere functionalities.