Fast Catalysis at Low Overpotential: Designing Efficient Dicationic Re(bpy 2+ )(CO) 3 I Electrocatalysts for CO 2 Reduction.

We report a series of isomeric, dicationic Re(bpy 2+ )(CO) 3 I complexes with bpy (2,2'-bipyridine) modified by two phenyl-CH 2 -(NMe 3 ) + pendants with cations located at variable distances from the active site for electrocatalytic CO 2 reduction in CH 3 CN/2.8 M H 2 O. The position of the cationic groups dramatically increases the rate of catalysis by ∼800-fold, from 1.2 to 950 s -1 , with only a minor increase in overpotential. Acceleration is due to stabilization of the initial CO 2 adduct and lowering of Δ G ‡ for C-OH bond cleavage by Coulombic stabilization of anionic charges. Performance may be enhanced by accumulation in the electrochemical double layer. Transition state stabilization in the optimized isomer unlocks the low overpotential "protonation-first" pathway, highlighting the sizable effects of subtle structural optimization.