Heterobi- and Heterotrimetallic Transition Metal Complexes with Carbon-Rich Bridging Units

Abstract

The syntheses of heterobi- and heterotrimetallic complexes based on (2,2‘-bipyridine-5-ylethynyl)ferrocene (3) are described. Complex 3 is accessible by the Pd(II)/Cu(I)-catalyzed Sonogashira cross-coupling of FcC⋮CH (1) (Fc = (η5-C5H4)(η5-C5H5)Fe) with 5-bromo-2,2‘-bipyridine (2). The complexation behavior of 3 was investigated. Treatment of 3 with (nbd)Mo(CO)4 (4a) (nbd = norbornadiene) at 25 °C, or refluxing 3 with Mn(CO)5Br (4b), (Me2S)2PtCl2 (4c), and Ru(bipy)2Cl2·2H2O (4d) (bipy = 2,2‘-bipyridine), respectively, gave the respective heterobimetallic complexes FcC⋮C-bipy(MLn) (5: MLn = Mo(CO)4, 6: MLn = Mn(CO)3Br, 7: MLn = PtCl2, 8: MLn = [Ru(bipy)2](PF6)2). Heterotrimetallic FcC⋮C-bipy{[Pt(μ-σ,π-C⋮CSiMe3)2]CuFBF3} (12) can be obtained by the subsequent reaction of 7 with Me3SiC⋮CH (9) and [Cu(N⋮CMe)4]BF4 (11), while [FcC⋮C-bipy{[Ti](μ-σ,π-C⋮CSiMe3)2}M]X (14a: M = Cu, X = PF6; 14b: M = Ag, X = ClO4; [Ti] = (η5-C5H4SiMe3)2Ti) were formed by combining 3 with {[Ti](μ-σ,π-C⋮CSiMe3)2}MX (13a: MX = Cu(N⋮CMe)PF6, 13b: MX = AgOClO3). The identity of 3, 10, and 14a was confirmed by single-crystal X-ray structural studies. The main characteristic features of 3 and 10 are the almost eclipsed conformation of the ferrocene cyclopentadienyl rings, the linear CCp−C⋮C−Cbipy moieties, and the coplanarity of both the pyridine and the C5H4 rings. The latter structural motif allows an optimal overlap between the π-orbitals of the cyclopentadienyl, ethynyl, and pyridyl rings. However, in 14a the bipy ligand is tilted by 96.9° toward the η5-C5H4 unit, which most likely is attributable to cell-packing effects. The platinum atom in 10 is held in a somewhat distorted square-planar surrounding. The chelated copper(I) ion in 14a possesses a pseudotetrahedral coordination geometry. Mononuclear 3 exhibits redox peaks in its cyclic voltammogram (E0 = 0.10 V, ΔEp = 194 mV) for the Fe2+/Fe3+ redox couple of the Fc unit and for the bipy ligand (E0.1 = −2.36 V, ΔEp = 200 mV; E0.2 = −2.76 V, ΔEp = 430 mV). Compounds 10, 12, 14a, and 14b additionally show electrode potentials attributed to the respective MLn building blocks.