Synthesis and Characterization of Multiferrocenyl-Substituted Group 4 Metallocene Complexes

The reaction of different metallocene fragments [Cp2M] (Cp=eta(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 [Cp2Ti(eta(2)-FcC(2)Fc)] (1) and [Cp2Ti(eta(4)-FcC(4)Fc)] (2) (Fc=[Fe(eta(5)-C5H4)(eta(5)-C5H5)]) by addition of the appropriate alkyne or diyne to Cp2Ti. Zirconocene precursors react with diferrocenyl- and ferrocenylphenylacetylene under C-C bond coupling to yield the metallacyclopentadienes [Cp2Zr-(C(4)Fc(4))] (3) and [Cp2Zr(C(4)Fc(2)Ph(2))] (5), respectively. The exchange of the zirconocene unit in 3 by hydrogen atoms opens the route to the super-crowded ferrocenyl-substituted compound tetra-ferrocenylbutadiene (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 [{Cp2Zr(mu-eta(1):eta(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.