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"A New Approach to Electrocatalytic CO2 Reduction Based on Supramolecular, Dinucleating Catalysts"

Final Report Summary - CO2REDUCTDINUCLEAT (A New Approach to Electrocatalytic CO2 Reduction Based on Supramolecular, Dinucleating Catalysts)

The research program for the first year was focused on two main objectives:
- Synthesis of novel rigid ligands derived.
- Synthesis and characterization of transition metal complexes derived from the aforementioned ligands.

During the first year, we have prepared a new family of ligands as we proposed in our project. But not all of these ligands have showed proper ability for coordinating two metal centers as we expected. However, some of them have the adequate properties to generate bimetallics as 1, 2 and 3 (Scheme1) or multimetallics complexes as 4 and 5 (Scheme 1). To sum up, we have prepared bi- tri and tetranuclear complexes in good yields (Scheme 1) under mild conditions in a very straigthforward manner. We have studied their reactivity with water and carbon dioxide.
Interestingly, one of the complexes react with water to give, to the best of our knowledge, the first m4-oxo-bridged-tetracopper(I) 4. All the complexes have been fully characterized by NMR spectroscopy, X-ray crystallography, ESI-HRMS (high resolution electrospray mass spectrometry) and elemental analysis.
The first stage of this proposal has covered properly the programmed two aims mentioned above. We wish that in the second stage the next ambitious aims will be achieved succcessfully.

The research program for the second year was focused on the application of the transition metal complexes as catalysts for reduction of CO2.

During the second year we have shown that the complexes based on structure 1 react with NaH▪BR3 to provide the copper hydride 3 which react with CO2 to generate the formate derivates 4. This process can be catalytic if silane is introduced in the reaction crude, producing the silyl formate and regenerating the copper hydride 3 (Scheme 1). We have evaluated a variety of reaction conditions such as solvent, temperature, catalyst load of 3 and different silane derivatives. The best results were obtained with ethylsilane at -60 ºC, 0.1% of catalyst load and 2 bars of CO2, obtaining a remarkable yield of 95 %.
In addition, complexes 2, 5 and 6 were evaluated in the selective activation of CO2 (Scheme 1). Complex 2 showed reaction with CO2, but in a stoichiometric ratio, probably due to the fact that carbon dioxide is activated between the carbene and the metal center. In contrast, complexes 5 and 6 did not show ability to activate CO2. This lack of reactivity was ascribed to the stronger interaction between the carbene and the metal center, which avoids the activation.
In conclusion, we have generated different bimetallics complexes based on naphthyridine skeleton, main goal of the IOF project, where some of them have shown extraordinary ability to activate carbon dioxide. Furthermore, complexes 3 can have showed that can transform carbon dioxide in a catalytically way into formate derivates.