Investigating metallocofactor dynamics with biomimetic dinuclear cobalt complexes

Abstract

Hydrogen-bond (H-bond) networks play a critical role in nature, allowing enzymatic active sites to sequester substrates; control high-energy intermediates; and maintain structure, be it flexible or rigid. This work reports a series of dinuclear cobalt complexes: [Co2(μ–OH)2(μ-OAc)(κ1-OAc)2(pyR)4][PF6] (1R) where OAc = acetate and pyR = pyridine with para-substituent R. Complexes within the series span a range of electron-donating and withdrawing R groups, and are able to serve as structural models for a wide class of oxidase enzymes that feature an M2(µ-OH)2 diamond core. Critically, complexes within the series mimic scaffolds found in nature in that they are stabilized by H-bond interactions between μ–OH donors and κ1-OAc acceptors. The mechanism of reactivity is yet unknown, but the disruption of these networks via deprotonation has been studied in organic solvents, revealing a significant correlation between the electronics of the distal pyR upon the trans H-bonding network. The optimized conditions for the synthesis of the series are reported, and by affording the complex water-solubility via counterion exchange, the interconnected nature of solution pH and the resultant strength of the H-bonding network has also been explored. Efforts to extend the synthesis of the series into the heterobimetallic regime are not yet successful, but the presented results suggest that the μ–OH pKa can be tuned in the presence of intramolecular H-bond interactions to maintain stability and serve as a model for natural motifs.