Hochreaktive Zwischenverbindungen aus Cokondensationsreaktionen von Eisen‐, Cobalt‐ und Nickeldämpfen mit Arenen

A Simple and Highly Efficient Iron Catalyst for a [2+2+2] Cycloaddition to Form Pyridines

“…Two important steps are generally involved in [2+2+2] cycloaddition: 1) formation of a metallacycle intermediate by oxidative cyclization and 2) subsequent reductive elimination to produce pyridines (the “common mechanism”) 2. The formation of a metallacycle intermediate12, 13 from a low‐valent metal species plays a crucial role in the whole process. Inspired by an investigation by Holland and co‐workers revealing that alkynes bind more tightly than phosphines to low‐valent iron center,14 we envisioned that low‐valent iron catalysts generated in situ from an inorganic iron salt and phosphine ligands might initiate the reaction through ligand exchange, and thereby promote the oxidative cyclization between an alkyne and an alkyne or a nitrile followed by the formation of metallacycle intermediate (Scheme , Step 2).…”

CH Activated Isomers of [M(AlCp*)5] (M=Fe, Ru)

“…[8] Thus we concentrated our attention on complexes of the type [Fe(AlCp*) n ] and chose [Fe(h 6 -toluene)(h 4 -1,3-butadiene)] as the Fe 0 source for the introduction of AlCp*. [9] If a red suspension of [Fe(h 6 -toluene)(h 4 -1,3-butadiene)] and six equivalents of AlCp* in toluene is heated to 80 8C (Scheme 1), an orange solution is rapidly formed. The 1 H NMR spectroscopic data point to a mixture of two products in the ratio of 3:1, neither of which has the structure [Fe(AlCp*) 5 ]!…”

A Simple and Highly Efficient Iron Catalyst for a [2+2+2] Cycloaddition to Form Pyridines

“…To gather evidence to support one of these hypotheses, two intermolecular [2+2+2] cycloaddition reactions were carried out (Scheme 4). As expected, cyclotrimerization of monoalkynes exclusively produced the 1,2,4-trisubstituted benzene 11 in 55 % yield, and indicated that a ferracyclopentadiene intermediate [12] was formed during cycloaddition [Scheme 4, Eq. (2)].…”

“…Herein, we disclose the [2+2+2] cycloaddition of diynes and unactivated nitriles at room temperature using a simple iron salt as the catalyst precursor, thus resulting in the production of pyridines with up to 98 % yield of isolated product.Two important steps are generally involved in [2+2+2] cycloaddition: 1) formation of a metallacycle intermediate by oxidative cyclization and 2) subsequent reductive elimination to produce pyridines (the "common mechanism"). [2] The formation of a metallacycle intermediate [12,13] from a low-valent metal species plays a crucial role in the whole process. Inspired by an investigation by Holland and co-workers revealing that alkynes bind more tightly than phosphines to low-valent iron center, [14] we envisioned that low-valent iron catalysts generated in situ from an inorganic iron salt and phosphine ligands might initiate the reaction through ligand exchange, and thereby promote the oxidative cyclization between an alkyne and an alkyne or a nitrile followed by the formation of metallacycle intermediate (Scheme 1, Step 2).…”