Metal bipyridine/terpyridine-containing

CREATIVE EXPLORATIONS OF TOPOLOGY FROM METAL BIPYRIDINE- AND TERPYRIDINE-CONTAINING DENDRIMERS TO OFF-CENTER FERROCENES... 

The intercalation of platinum complexes containing bidentate or tridentate aromatic amines was first proposed for binding to tRNA and then to DNA [53]. The structures of the relevant complexes of palladium and platinum are shown in Figure 1.5 and a requisite is the presence of planar ligands such as bipyridine, terpyridine, or o-phenanthroline, which are coplanar with the coordination plane formed by the four ligand donor atoms and the metal ion. The similar pyridine derivative, [Pt(en)py2], where the pyridine Ugands are forced by nonbonded steric constraints to be out of the coordination plane, does not intercalate. 

Schubert US, Eschbaumer C Angew Chem Int Ed (2002) 41 2892-2926 Macromolecules containing bipyridine and terpyridine metal complexes towards metallo-supramolecular polymers... 

Pyridine-based ligands which have been used for dendrimers are 2,2-bipyridine (bpy) 17,2,3-bis(2-pyridyl)pyrazine (2,3-dpp) 18 and its monomethylated salt 19, and 2,2 6, 2"-terpyridine 20. Their transition metal complexes possessing dendritic structures were first reported in the collaborative work of Denti, Campagne, and Balzani whose divergent synthetic strategy has led to systems containing 22 ruthenium centers. - The core unit is [Ru(2,3-dpp)3] 21 which contains three... 

Fluorescent redox switches based on compounds with electron acceptors and fluorophores have been also reported. For instance, by making use of the quinone/ hydroquinone redox couple a redox-responsive fluorescence switch can be established with molecule 19 containing a ruthenium tris(bpy) (bpy = 2,2 -bipyridine) complex.29 Within molecule 19, the excited state of the ruthenium center, that is, the triplet metal-to-ligand charge transfer (MLCT) state, is effectively quenched by electron transfer to the quinone group. When the quinone is reduced to the hydroquinone either chemically or electrochemically, luminescence is emitted from the ruthenium center in molecule 19. Similarly, molecule 20, a ruthenium (II) complex withhydroquinone-functionalized 2,2 6, 2"-terpyridine (tpy) and (4 -phenylethynyl-2,2 6, 2"- terpyridine) as ligands, also works as a redox fluorescence switch.30... 

Despite the extensive application of ruthenium complexes in DSSC, transition metal containing polymers have received relatively little attention in the fabrication of polymeric photovoltaic cells. Most of the early works on ruthenium containing polymers were focused on the light-emitting properties.58-60 Several examples of ruthenium terpyridine/bipyridine containing conjugated polymers and their photoconducting/electroluminescent properties were reported.61,62... 

It should be noted that a number of SPC polymers which contain other heterocycles have been prepared, motivated by their promising optical or electrical properties. Examples include pyridine (65) [123], pyrrole (66) [124], oxadiazole (67) [125], selenophene (68) [126], benzo[2,l,3]thiadiazole (69) [127], benzo[2,l,3]selenadiazole (70) [126], perylene bisimide (71) [128], 1,4-diketo- pyrrolo[3,4-c]pyrrole-l,4-dione (72 and 73) [127,129], and triphenyleamine (74) [127] as part of the polymer backbone by SPC (Figure 19c). Specifically for metal complexation, porphyrin [130], difluoroboraindacene [131], bipyridine [132], phenanthroHne [113], terpyridine [133, 134], and the like [123] were embedded in the backbone. In this context, an interesting report was submitted by Rehahn et al., in which l,l -ferrocenyl units were incorporated into a PPP (Figure 22.20). Due to a low-energy barrier for rotation around the Cp-Fe-Cp axes (Cp = cyclopentadienyl), the obtained polymer 75 was assumed to take randomly coiled conformations [135]. 

U. S. Schubert and C. Eschbaumer, Macromolecules containing bipyridine and terpyridine metal complexes towards metaUosupramolecular polymers, Angew. Chem. Int. Ed, 41, 2892—2926 (2002). 

Three generations of dendritic molecules constructed around an Fe(II) bis-terpyri-dine core were synthesized by Chow et al., and it was found that the Fe(II/III) redox process became more (electrochem-ically) irreversible as the generation of the dendrimer increased [39]. Ruthenium bis-terpyridine ([Ru(tpy)2] ) [40] and ruthenium tris-bipyridine ([Ru(bpy)3]+ ) moieties [41, 42] have also been used as central anchor points around which hyper-branched macromolecules may be created. In studies of the [Ru(bpy)3]+ -containing compounds, the metal-localized oxidation process (Ru(II/III)) became more electro-chemically irreversible as the size of the dendritic sheath increased [42]. 

Figure 18 Schematic representation of the formation of supramolecular coordination polymers of main-chain or side-chain type from iigands containing bidentate and/or tridentate complexation subunits (such as bipyridine and terpyridine) binding metal ions of tetra-, penta-, or hexa-coordination, and of the constituting subunits. Dynamic diversity may be generated by scrambling of different ligand monomers.

Review Schubert, U.S. and Eschbaumer, C. (2002) Macromolecules containing bipyridine and terpyridine metal complexes Towards metaUosupramolecular polymers. Angewandte Chemie-International Edition, 41,2893. 

---