Altering the Catalytic Activity of a Monomeric Cu-Porphyrin Using Self-Assembly To Preorganize a Cubic Architecture.

Coordination-driven self-assembly is an efficient strategy for designing polynuclear structures with preorganized catalytic sites. Here, we explore the electrocatalytic behavior of a self-assembled copper porphyrin cube featuring iron nodes (Fe-Cu) using the carbon dioxide reduction reaction (CO2RR) and hydrogen evolution reaction (HER) as model transformations. Ultraviolet-visible (UV-vis) spectroscopy, cyclic voltammetry, spectroelectrochemical experiments, and XPS data revealed that Fe-Cu decompose to regenerate Cu-TAPP under catalytic conditions. The CO2RR versus HER activity of Fe-Cu was tested under heterogeneous conditions to preserve the preorganized cubic arrangement of porphyrins. Upon scission of the Fe-imine nodes, the catalytic activity of the constructed Fe-Cu differs from Cu-TAPP and physical mixtures of Fe(II) and Cu-TAPP. Like free Fe(II) salts, the Fe-Cu-based materials were more selective for the hydrogen evolution reaction (HER), whereas Cu-TAPP generated a mixture of CO2RR products. Spectroscopic methods were used to establish that the Fe-Cu releases Cu-TAPP under reducing conditions, making the shift in selectivity particularly notable since the same active species is present in both systems. This study illustrates the use of self-assembly to preorganize catalytic sites and exploits the limited molecular movement under heterogeneous conditions to preserve a polynuclear microenvironment despite operating under conditions where the assembly does not remain intact.