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 C-C 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 C-C bond, and thus, dinuclear [{Cp(2)Zr(µ-η(1):η(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.

Reactions of group 4 metallocene alkyne complexes with carbodiimides: experimental and theoretical studies of the structure and bonding of five-membered hetero-metallacycloallenes.

The reaction of the low-valent metallocene(II) sources Cp(2)Ti(η(2)-Me(3)SiC(2)SiMe(3)) (7) and Cp(2)Zr(py)(η(2)-Me(3)SiC(2)SiMe(3)) (11, Cp = η(5)-cyclopentadienyl, py = pyridine) with carbodiimides RN═C═NR (R = Cy, i-Pr, p-Tol) leads to the formation of five membered hetero-metallacycloallenes Cp(2)M{Me(3)SiC═C═C[N(SiMe(3))(R)]-N(R)} (9M-R) (M = Ti, R = i-Pr; M = Zr, R = Cy, i-Pr, p-Tol). Elimination of the alkyne (as the hitherto known reactivity of titanocene and zirconocene alkyne complexes would suggest) was not observed. The molecular structures of the obtained complexes were confirmed by X-ray studies. Moreover, the structure and bonding of the complexes 9Zr-Cy and 9Zr-p-Tol was investigated by DFT calculations.

(tert-Butyl-imido)bis-(η-cyclo-penta-dien-yl)pyridine-zirconium(IV).

The title compound, [Zr(C(5)H(5))(2)(C(4)H(9)N)(C(5)H(5)N)], was obtained from the reaction of (C(5)H(5))(2)Zr(py)(η(2)-Me(3)SiC(2)SiMe(3)) (py is pyridine) and (t)BuN=C=N(t)Bu alongside the formation of (C(5)H(5))(2)Zr(CN(t)Bu)(η(2)-Me(3)SiC(2)SiMe(3)). The zirconium atom is coordinated in a distorted tetra-hedral geometry by two cyclo-penta-dienyl ligands, a pyridine ligand, and a tert-butyl-imido ligand via a Zr=N double bond. The tert-butyl group is disordered over two positions in a 0.634 (5):0.366 (5) ratio.