The synthesis of a unique series of heteromultinuclear transition metal complexes with up to seven different metal atoms is reported by using consecutive synthesis methodologies including metathesis, dehydrohalogenation, and carbon−carbon cross-coupling reactions. In these compounds the metals Ti, Fe, Ru, Os, Re, Pt, and Cu are connected via carbon-rich bridging units comprising 1,3,5-triethynylbenzene and 2,2′-bipyridyl-5-yl. These molecules have been characterized by elemental analysis, IR and NMR spectroscopy, and ESI-TOF mass spectrometry. The main structural feature of these compounds is an unsymmetrical trans-configurated platinum(II) bis-acetylide unit. The structure of 1-(FcCC)-3-[( t Bu2bpy)(CO)3ReCC]-5-[trans-(Ph3P)2(RcCC)PtCC]C6H3 (3) and 1,3-[(Ph3P)2(η5-C5H5)OsCC]2-5-[(CO)3(Cl)Re(bpyCC)]C6H3 (18) (Fc = (η5-C5H5)(η5-C5H4)Fe; Rc = (η5-C5H5)(η5-C5H4)Ru; t Bu2bpy = 4,4′-di-tert-butyl-2,2′-bipyridyl; bpy = 2,2′-bipyridyl-5-yl) in the solid state is reported. Both compounds are characterized by the central 1,3,5-triethynylbenzene core, bridging the individual transition metal building blocks. These organometallic fragments show thereby typical structural properties. The appropriate metal acetylide moieties are, as expected, found in a linear arrangement with representative M−C and CC bond distances.

This review describes the synthesis, reaction chemistry, structures, and bonding of early-late heterodi-, heterotri-, and heterotetrametallic transition-metal complexes by applying the molecular "Tinkertoy" approach. As connecting units between the different metal atoms, π-conjugated carbon-rich organic and/ or inorganic groups can be used. The electrochemical behavior of such one-dimensional molecular wire molecules, coordination polymers, starlike structures, and dendritic oriented transition-metal species, respectively, is presented as well.

The synthesis and characterisation of a first heteromultimetallic transition metal complex with six different metal atoms (Fe, Ru, Re, Au, Cu and Ti), connected through carbon‐rich bridging units, are reported. Complex {1‐[(η2‐dppf)(η5‐C5H5)RuC≡C]‐3‐[(bipy*)(CO)3ReC≡C]‐5‐[PPh2AuC≡C‐bipy({[Ti](μ‐σ,π‐C≡CSiMe3)2}Cu)]C6H3}PF6 is accessible in a consecutive reaction sequence by applying building blocks from a ligand and coordination complex library. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

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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 crosscoupling of FcCtCH (1) (Fc ) (η 5 -C 5 H 4 )(η 5 -C 5 H 5 )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) 5 Br (4b), (Me 2 S) 2 PtCl 2 (4c), and Ru(bipy) 2 Cl 2 ‚2H 2 O (4d) (bipy ) 2,2′bipyridine), respectively, gave the respective heterobimetallic complexes FcCtC-bipy 12) can be obtained by the subsequent reaction of 7 with Me 3 SiCtCH ( 9) and [Cu(NtCMe) 4 ]BF 4 (11), while [FcCtC-bipy{[Ti](µ-σ,π-CtCSiMe 3 ) 2 }M]X (14a: M ) Cu, X ) PF 6 ; 14b: M ) Ag, X ) ClO 4 ; [Ti] ) (η 5 -C 5 H 4 SiMe 3 ) 2 Ti) were formed by combining 3 with {[Ti](µ-σ,π-CtCSiMe 3 ) 2 }MX (13a: MX ) Cu(NtCMe)PF 6 , 13b: MX ) AgOClO 3 ). 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 C Cp -CtC-C bipy moieties, and the coplanarity of both the pyridine and the C 5 H 4 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 η 5 -C 5 H 4 unit, which most likely is attributable to cell-packing effects. The platinum atom in 10 is held in a somewhat distorted squareplanar surrounding. The chelated copper(I) ion in 14a possesses a pseudotetrahedral coordination geometry. Mononuclear 3 exhibits redox peaks in its cyclic voltammogram (E 0 ) 0.10 V, ∆E p ) 194 mV) for the Fe 2+ /Fe 3+ redox couple of the Fc unit and for the bipy ligand (E 0.1 ) -2.36 V, ∆E p ) 200 mV; E 0.2 ) -2.76 V, ∆E p ) 430 mV). Compounds 10, 12, 14a, and 14b additionally show electrode potentials attributed to the respective ML n building blocks.