STABILIZED IRON CATALYSTS FOR C-C CROSS-COUPLING – SIROCCO

Iron catalysts are an inexpensive and non-toxic alternative to the noble-metal-based systems used in organometallic catalysis. This is particularly true in the field of C—C bond formation by cross-coupling reactions, which is mainly dominated by palladium catalysis. The incredible breakthrough which was brought by palladium chemistry in the field of organic synthesis was acknowledged by the Nobel Prize in 2010, awarded to Heck, Suzuki and Negishi. However, one of the main drawbacks of such methods remains the toxicity and the cost of the catalysts. The field of iron-catalyzed C—C bond formation, which was discovered by Kochi in the 1970s, is still in its infancy, and witnessed recent improvements thanks to the work of Fürstner, Nakamura and Bedford during the two last decades. Nevertheless, only a few systems leading to efficient cross-coupling reactions catalyzed by iron complexes are reported so far. These methods mainly involve highly reactive nucleophilic partners such as organolithium, organozinc or Grignard reagents, and, more rarely, softer partners such as organoboranes. The mechanistic understanding of these transformations is complex, due to the possible involvement of multiple low-valent iron species. Moreover, delineating the nature of the catalytic active species is difficult to tackle, since the iron complexes involved in these systems are often very sensitive, reactive, and prompt to undergo ligand scrambling or disproportionation processes leading to complex mixtures. Therefore, numerous mechanistic features of iron-catalyzed C—C cross-coupling reactions are still unknown. The first goal of this project is the investigation of the mechanistic features of simple ligand-free systems catalytically active in Kochi-type C—C cross-coupling reactions. On the basis of these results, new families of iron(I) complexes will be synthesized and investigated by means of EPR and Mössbauer spectroscopies and molecular electrochemistry, in order to rationalize the stereo-electronic effects governing their reactivity patterns. Additional theoretical studies, involving DFT and post Hartree-Fock calculations, will support these results. A focus will be made on the synthesis of arene-stabilized iron(I) complexes, since preliminary results revealed the role of such species in ligand-free catalytic reactions. The second goal of the SIROCCO project is the development of new and efficient C—C bond formation reactions catalyzed by the aforementioned iron(I)-based systems, with a particular focus on the development of cross-coupling processes involving mild (and therefore challenging) nucleophiles, such as trifluoroarylborates, enolates, and organosilanes, so far not used in iron catalysis.