Synthesis of Low-Spin Fe(II) NHC Complexes and Their Computational Evaluations in the Context of Olefin Metathesis

The development of Fe-based olefin metathesis has been a long-standing goal for several decades. Research from both experimental and theoretical groups has indicated that suitable Fe alkylidenes should be low-spin complexes with a high bond dissociation energy (BDE) for the Fe═C bond. In this study, we synthesized a series of low-spin Fe complexes featuring IMes (IMes = 1,3-dimesitylimidazol-2-ylidene), CN, and CO ligands, which have potential applications in the synthesis of Fe alkylidenes. We computationally investigated the corresponding Fe benzylidenes in the context of olefin metathesis. Although some of these complexes favor low-spin states and demonstrate high BDE, competing side reactions─such as cyclopropanation and carbene insertions─could impede their effectiveness in olefin metathesis.