Twin Porphyrins and Phthalocyanines: Breaking Limits in Molecular CO₂ Electrocatalysis with Metal-Metal Cooperation

• Applicant: Professor Dr. Franc Meyer
• Subject Area: Inorganic Molecular Chemistry - Synthesis and Characterisation
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 568819569

Electrochemical CO₂ reduction (CO₂RR) presents a promising route to convert CO₂ into valuable fuels and chemical feedstocks, facilitating renewable energy storage and promoting a carbon-neutral economy. Over the past decade, significant progress has been achieved in selectively producing C1 compounds (e.g., CO, formate) through a 2e⁻/2H⁺ reduction process. However, advancing beyond these products to generate super-reduced C1 species (e.g., methanol, methane) or multicarbon (C2+) compounds (e.g., ethylene, ethanol, propanol) is crucial for achieving higher energy density in the products, maximizing CO₂ utilization efficiency, and enhancing environmental benefits. Most molecular CO₂RR catalysts are mononuclear metal complexes, limiting CO₂ interaction to a single active site. This hinders the tandem strategy, i.e., the simultaneous reduction and coupling of CO₂ molecules essential for C–C bond formation or the generation of a nearby metal hydride to reduce a M-CO intermediate further. To overcome these limitations, this project aims to develop efficient catalysts capable of selectively producing super-reduced or C2+ products by designing homo- and heterodinuclear complexes that exploit metal-metal cooperativity. Specifically, we will build on the well-established mononuclear porphyrin- and phthalocyanine-based CO₂RR catalyst motifs, focusing on their "Siamese twin" counterparts, a challenging yet promising strategy. These ligands, based on pyrazole-expanded porphyrins or phthalocyanines, provide two adjacent cavities, each featuring an {N4} coordination environment. This unique design should provide a robust bimetallic scaffold and enable control over the orientation and distance between the two cooperating metal centers to achieve optimal production of highly reduced C1 and C2+ compounds. Through rational modifications of the macrocyclic ligand framework, a detailed structure-activity relationship study, and mechanistic investigation, we will identify key parameters for achieving high efficiency and selectivity toward super-reduced CO₂ products and C2+ compounds. Additionally, to enhance sustainability and catalyst stability, we will immobilize the most promising catalysts onto carbon nanotube (CNT) materials, creating heterogeneous CO₂RR systems that operate in aqueous solutions. This ambitious project builds upon the combined expertise of the two research groups. The German partner has synthesized and characterized some first dinuclear Siamese twin complexes, though they remain untested in catalysis. Meanwhile, the French partner has developed a unique heterodinuclear NiFe molecular catalyst that successfully applies a tandem mechanism to produce methane as the sole carbon-based product. By integrating these complementary approaches, we aim to pioneer new catalytic strategies for CO₂ conversion, enhancing the potential of this method to deliver more sustainable environmental solutions and significantly reduce the carbon footprint.

• DFG Programme: Research Grants
• International Connection: France
• Cooperation Partners: Dr. Carole Duboc; Dr. Noemie Lalaoui