Synthesis and characterization of multiferrocenyl-substituted group 4 metallocene complexes

摘要

The reaction of different metallocene fragments [Cp _2M] (Cp=?· ~5-cyclopentadienyl, M=Ti, Zr) with diferrocenylacetylene and 1,4-diferrocenylbuta-1,3-diyne is described. The titanocene complexes form the highly strained three- and five-membered ring systems [Cp _2Ti(?· ~2-FcC _2Fc)] (1) and [Cp _2Ti(?· ~4-FcC _4Fc)] (2) (Fc=[Fe(?· ~5-C _5H _4) (?· ~5-C _5H _5)]) by addition of the appropriate alkyne or diyne to Cp _2Ti. Zirconocene precursors react with diferrocenyl- and ferrocenylphenylacetylene under C-C bond coupling to yield the metallacyclopentadienes [Cp _2Zr(C _4Fc _4)] (3) and [Cp _2Zr(C _4Fc _2Ph _2)] (5), respectively. The exchange of the zirconocene unit in 3 by hydrogen atoms opens the route to the super-crowded ferrocenyl-substituted compound tetraferrocenylbutadiene (4). On the other hand, the reaction of 1,4-diferrocenylbuta-1,3-diyne with zirconocene complexes afforded a cleavage of the central C-C bond, and thus, dinuclear [{Cp _2Zr(μ- ?· ~1:?· ~2-C≡CFc)} _2] (6) that consists of two zirconocene acetylide groups was formed. Most of the complexes were characterized by single-crystal X-ray crystallography, showing attractive multinuclear molecules. The redox properties of 3, 5, and 6 were studied by cyclic voltammetry. Upon oxidation to 3 ~(n+), 5 ~(n+), and 6 ~(n+) (n=1-3), decomposition occured with in situ formation of new species. The follow-up products from 3 and 5 possess two or four reversible redox events pointing to butadiene-based molecules. However, the dinuclear complex 6 afforded ethynylferrocene under the measurement conditions. Super-crowded metallocenes: The reaction of diferrocenylacetylene and 1,4-diferrocenylbuta-1,3-diyne with Group 4 metallocene compounds yields attractive multiferrocenyl complexes. Depending on the metal, different products were obtained by complexation, coupling, or C-C bond cleavage of the ligand (see scheme). Their electrochemical properties were studied in detail. The oxidation of the metallacycle induces decomposition of the complexes.