Reversibly Modulating the Selectivity of Carbon Dioxide Reduction via Ligand-Driven Spin Crossover.

Selectivity is an essential aspect in catalysis. At present, the improvement of the selectivity for complex reactions with multiple pathways/products, for example the carbon dioxide reduction reaction (CO2RR), can usually be achieved for only one pathway/product. It is still a challenge to reversibly modulate the selectivity between two reaction pathways or products of the CO2RR by one catalyst. Here, we propose the reversible modulation of selectivity between two products via spin crossover. By employing first-principles calculations, six spin crossover molecular catalysts are found among 17 kinds of transition metal embedded porphyrin derivatives (ppy_TM), where the changes in axial ligand configurations can reversibly switch the spin state of catalysts between high spin and low spin. For ppy_Os and ppy_Ru, the alteration in spin state can effectively influence the reduction of CO2 into either formic acid or carbon monoxide by changing the relative stability of the key intermediates *COOH and *HCOO.