2,2 :6, 2"-Terpyridine, ligand structure

It has been mentioned previously that the formation of 2 1 Co 02 -peroxodimers is generally believed responsible for the irreversible coordination of dioxygen. In apparent contrast with this affirmation, the mixed bipyridine/terpyridine ligands complex [ Co(terpy)(bipy) 2 (fi-02)]4 +, the molecular structure of which is shown in Figure 16, constitutes an example of reversible coordination of the peroxo group.22... 

We selected two types of molecular wires to form desired structures for the electrode. The first has a linear structure with a bis-terpyridine moiety (Lp azobenzene-bridged bis-terpyridine ligand, L2 phenylene-bridged bis-terpyridine ligand), as illustrated in Figure 2. This type of wire can form a linear structure such as a bead curtain. The second has a triangular structure with three terpyridine... 

Mention is made here to a member of a series of dimeric terpyridine plati-num(Il) complexes, [(tpy)Pt( -pz)Pt(tpy)](C104)3, 226. These complexes were used to study the effect of the Pt Pt separation on absorption and emission spectra (170, 171). The X-ray crystal structure of Complex 226 was determined A single pyrazolate ligand bridges two Pt centers. The square planar coordination around each metal is completed by a tridentate terpyridine ligand (170). 

Figure 14 Synthesis of tritopic terpyridine ligands 52—54 using the Sonogashira coupling and their self-assembly into cage structures 55—57 under thermodynamic control with IVl = Zn". Energy minimized structures and dimensions and 2D DOSY NMR spectra of 55 (left), 56 (middle), and 57 (right). Adapted with permission from Ref. 14JA10499. Copyright 2014 American Chemical Society.

Fig. 2 Structures of the polytopic ligand molecules based on terpyridine (1,7,8), pyrazolypyiidine (2-4), pyridine-2,6-dicarboxylic acid (5), Schiff base (6), and phenanthroline (9) ligands. Note, that 1-6 and 9 are ditopic ligands (bisligands), and that 7 and 8 are three-head ligands. Structures 4 and 5 are flexible and water-soluble, and the others are all rigid. In molecule 5, when m = 3, it is denoted as L2EO4...

Kwong and Lee [39] prepared various chiral 2,2 6, 2"-terpyridines and tested them as copper ligands for the cyclopropanation of alkenes. High enantioselectivities were obtained, the presence of bulky alkyl groups at the 8-position of the tetrahydroquinoline ring being crucial (structure 29 in Scheme 17). Thus when = Bu, up to 90% ee for the trans and 94% for the cis isomer were obtained by performing the reaction at 0 °C (transIds = 69/31). 

In contrast to 6-substituted-bipyridine systems such as 49, attachment of a five-membered heterocycle to the 2-position of 1,10-phenanthroline, which is a structural modification similar to the replacement of one of the terminal rings of terpyridine, does generally bring the ligand field into the crossover region and spin transitions have been observed for such systems when the heterocycle is thiazole 51 [74], imidazoline [75], triazole [76], pyrazole [77] and oxadiazole [78]. 

In most cases, metal ion coordination by a dendrimer takes place by units that are present along the dendrimer branches (e.g., amine, imine, or amide groups) or appended at the dendrimer periphery (e.g., terpyridine, cathecolamide ligands). When multiple identical coordinating units are present, dendrimers give rise to metal complexes of variable stoichiometry and unknown structures. Luminescent dendrimers with a well defined metal-coordinating site have been reported so far [16, 17], and the most used coordination site is 1,4,8,11-tetraazacyclotetradecane (cyclam). 

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