Synthesis and Characterization of Multiferrocenyl‐Substituted Group 4 Metallocene Complexes

The reaction of different metallocene fragments [Cp 2 M] (Cp=η 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 2 Ti(η 2 ‐FcC 2 Fc)] ( 1 ) and [Cp 2 Ti(η 4 ‐FcC 4 Fc)] ( 2 ) (Fc=[Fe(η 5 ‐C 5 H 4 )(η 5 ‐C 5 H 5 )]) by addition of the appropriate alkyne or diyne to Cp 2 Ti. Zirconocene precursors react with diferrocenyl‐ and ferrocenylphenylacetylene under CC bond coupling to yield the metallacyclopentadienes [Cp 2 Zr(C 4 Fc 4 )] ( 3 ) and [Cp 2 Zr(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 tetraferrocenylbutadiene ( 4 ). On the other hand, the reaction of 1,4‐diferrocenylbuta‐1,3‐diyne with zirconocene complexes afforded a cleavage of the central CC bond, and thus, dinuclear [{Cp 2 Zr(μ‐η 1 :η 2 ‐CCFc)} 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.