The "metathesis reaction" is a straightforward and often metal-catalyzed chemical reaction that transforms two hydrocarbon molecules to two new hydrocarbons by exchange of molecular fragments. Alkane, alkene and alkyne metathesis have become an important tool in synthetic chemistry and have provided access to complex organic structures. Since the discovery of industrial olefin metathesis in the 1960s, many modifications have been reported; thus, increasing scope and improving reaction selectivity. Olefin metathesis catalysts based on high-valent group six elements or Ru(IV) have been developed and improved through ligand modifications. In addition, significant effort was invested to realize olefin metathesis with a non-toxic, bio-compatible and one of the most abundant elements in the earth's crust; namely, iron. First evidences suggest that low-valent Fe(II) complexes are active in olefin metathesis. Although the latter has not been unambiguously established, this review summarizes the key advances in the field and aims to guide through the challenges.

ortho‐Terphenyls are of high interest for medicinal chemistry and materials science, but they are difficult to access. Herein, we demonstrate a straightforward and sustainable synthesis of highly functionalized ortho‐terphenyls via joining an organocatalyzed two‐step domino reaction (Knoevenagel/vinylogous Michael) with a DABCO/CuBr2 co‐catalyzed three‐step domino reaction (cyclization/tautomerization/aromatization) in a one‐pot process. Overcoming necessity to isolate intermediate products leads to a reduction of energy, costs and waste for a broad scope of reactions. DFT calculations have been performed to investigate the thermodynamics of this one‐pot process towards ortho‐terphenyls and to study the reaction profile of the vinylogous Michael reaction under inclusion of solvent effects. Role of London dispersion forces in this transformation has been elucidated. It is shown that reaction kinetics and thermodynamics are slightly influenced by dispersion interactions. Furthermore, the addition of dispersion energy donors leads to small changes of reaction energies in some cases.

Olefin metathesis gives access to important petrochemicals, polymers, and pharmaceuticals. The catalysts for these transformations are often based on high‐valent metal ions e.g., Ru(IV), which have been improved through ligand modifications. An attractive, but challenging goal is to catalyze olefin metathesis with a non‐toxic, bio‐compatible, and abundant element; namely, iron. Indeed, the first pieces of evidence suggest that low‐valent Fe(II) complexes are active in olefin metathesis. This Review by K. Meyer, S. B. Tsogoeva, et al. (DOI: 10.1002/chem.202201414) summarizes the key advances and challenges in this endeavor.