Binuclear Iron Complexes for challenging CATalytic reactions – BICCCAT

The common feature of these catalysts is the presence of diiron sites supported by macrocyclic (phthalocyanine, porphyrin) or non-heme ligands which form catalytically active high-valent diiron species. They have been evidenced by advanced spectroscopic methods and characterized by DFT calculations by project partners. We have shown the superiority of the diiron systems over their mononuclear counterparts. However, many bottlenecks still remain (reaction scope and selectivity, catalysts life span, operating conditions, ...). In-depth investigation of these systems is thus necessary to get a deeper insight into the reactions and further improvements of the catalysts for challenging reactions.

1.Demonstration of catalytic activity of µ-oxo, µ-nitrido and µ-carbido complexes in the reactions of carbene transfer (cyclopropanation of olefins, insertion to N-H bonds). Application of binuclear diiron macrocyclic complexes for these reactions has been shown for the first time.
2. Demonstration of catalytic activity of macrocyclic carbenic complexes for nitrene transfer reactions.

Novel heme and non-heme diiron catalysts will be developed on the basis of our present knowledge of oxygen and nitrene transfer to C-H bonds. Improving the efficiency of these reactions in mild and green conditions is the objective. For halogenation and dehalogenation reactions we will pursue the search for efficient catalysts and operation conditions. (ii) A new generation of catalysts will be designed by using a nitrido bridge to team up mixed assemblies of iron porphyrin-like macrocycles and non-heme iron systems. Benefiting from the robustness of the former and the versatility of the latter, such systems are likely to provide interesting advances and improvements. The optimization of the catalytic systems and the development of practical applications will be based on new fundamental knowledge of the mechanisms using state-of-the-art spectroscopic and computational studies. Consequently, we believe that successful project development will provide new fundamental insights in this highly competitive field and the scientific basis for innovative chemistry to lead to efficient and energy saving industrial processes based on iron, a cheap, non toxic and earth-abundant metal.

1. C. Colomban, A. B. Sorokin. Comparison of µ-nitrido diiron phthalocyanine – H2O2 and Fenton system in transformation of poly- and perfluorinated aromatics does not support the involvement of hydroxyl radicals. J. Coord. Chem. 2018, DOI : 10.1080/00958972.2018.1467009.
2. A. P. Kroitor, L. P. Cailler, A. G. Martynov, A. G. Gorbunova, A. Yu. Tsivadze, A. B. Sorokin. Unexpected formation of µ-carbido diruthenium(IV) complex during metalation of phthalocyanine with Ru3(CO)12 and its catalytic activity in the carbene transfer reactions. Dalton Trans. 2017, 46, 15651-15655.
3. C. Colomban, E. V. Kudrik, A. B. Sorokin. Heteroleptic µ-nitrido diiron complexes supported by phthalocyanine and octapropylpo-rphyrazine ligands: formation of oxo species and their reactivity with fluorinated compounds. J. Porphyrins Phthalocyanines 2017, 21, 345-353.
4. A. B. Sorokin. µ-Nitrido diiron phthalocyanine and porphyrin complexes : unusual structures with interesting catalytic properties. In Advances in Inorganic Chemistry, Ed. R. van Eldik, Elsevier, 2017, vol. 70, pp. 107-165.

This project is devoted to design robust and efficient catalysts for performing challenging reactions under clean and mild conditions yet unavailable in chemical industry. We will develop an approach inspired by Nature which performs under physiological conditions difficult processes (e.g. methane oxidation, sMMO) or highly selective ones (e.g. hydroxylations by cytochromes P450 and halogenations by non-heme iron enzymes. Cytochromes P450 are able also to catalyze nitrene transfers, reactions conceptually analogous to hydroxylations.
We have recently developed a novel concept based on combining the structures of the two most efficient enzymes in oxidation by assembling two iron atoms (as in sMMO) within macrocycling ligands (as in P450). This concept was validated by our discovery of remarkable catalytic properties of N-bridged diiron phthalocyanine and porphyrin complexes (PFeIII(µ-N)FeIVP) for the mild oxidation of methane C-H bond by H2O2 in water with turnover numbers up to 500. Aromatic C-F bonds can also be activated in oxidative conditions provided by these diiron complexes and H2O2, enabling high defluorination of a wide range of poly- and perfluorinated aromatics which are among the most stable organic molecules. Oxidative defluorination thus appears as a fundamentally new type of the activation of C-F bonds. The Fe(µN)Fe structural feature is essential for this outstanding reactivity.
Non-heme diiron complexes have been less studied and their potential has not yet been fully revealed. Indeed, we recently showed that non-heme diiron sites show remarkable activity in nitrene transfer reactions which are of utmost importance for the synthesis of biologically and pharmacologically active amines. Nitrene transfer can be activated by oxo transfer reagents, which opens the way to catalyze the transfer reactions of different groups.
The common feature of these catalysts is the presence of diiron sites supported by macrocyclic (phthalocyanine, porphyrin) or non-heme ligands which form catalytically active high-valent diiron species. They have been evidenced by advanced spectroscopic methods and characterized by DFT calculations by project partners. We have shown the superiority of the diiron systems over their mononuclear counterparts in catalysis. However, many bottlenecks still remain (reaction scope and selectivity, catalysts life span, operating conditions, ...). In-depth investigation of these systems is thus necessary to get a deeper insight into the reactions and further improvements of the catalysts for challenging reactions: oxidation of methane, transformation of fluorinated aromatic compounds in oxidative conditions, selective halogenations of organic compounds, preparation of nitrogen compounds by transformation of C-H bonds to C-N bonds.
Novel heme and non-heme diiron catalysts will be developed on the basis of our present knowledge of oxygen and nitrene transfer to C-H bonds. Improving the efficiency of these reactions in mild and green conditions is the objective. For halogenation and dehalogenation reactions we will pursue the search for efficient catalysts and operation conditions. (ii) A new generation of catalysts will be designed by using a nitrido bridge to team up mixed assemblies of iron porphyrin-like macrocycles and non-heme iron systems. Benefiting from the robustness of the former and the versatility of the latter, such systems are likely to provide interesting advances and improvements. The optimization of the catalytic systems and the development of practical applications will be based on new fundamental knowledge of the mechanisms using state-of-the-art spectroscopic and computational studies. Consequently, we believe that successful project development will provide new fundamental insights in this highly competitive field and the scientific basis for innovative chemistry to lead to efficient and energy saving industrial processes based on iron, a cheap, non toxic and earth-abundant metal.