2,2 :6 ,2"-Terpyridine, formation

From the dimensions of the lattice of W-6 Raney nickel, it seems that the formation of 2,2 6, 2"-terpyridine would be expected when one molecule of 2,2 -bipyridine and one molecule of pyridine are... 

A general strategy developed for the synthesis of supramolecular block copolymers involves the preparation of macromolecular chains end-capped with a 2,2 6/,2//-terpyridine ligand which can be selectively complexed with RUCI3. Under these conditions only the mono-complex between the ter-pyridine group and Ru(III) is formed. Subsequent reaction with another 2,2 6/,2"-terpyridine terminated polymer under reductive conditions for the transformation of Ru(III) to Ru(II) leads to the formation of supramolecular block copolymers. Using this methodology the copolymer with PEO and PS blocks was prepared (Scheme 42) [ 107]. 

Several approaches have been undertaken to construct redox active polymermodified electrodes containing such rhodium complexes as mediators. Beley [70] and Cosnier [71] used the electropolymerization of pyrrole-linked rhodium complexes for their fixation at the electrode surface. An effective system for the formation of 1,4-NADH from NAD+ applied a poly-Rh(terpy-py)2 + (terpy = terpyridine py = pyrrole) modified reticulated vitreous carbon electrode [70]. In the presence of liver alcohol dehydrogenase as production enzyme, cyclohexanone was transformed to cyclohexanol with a turnover number of 113 in 31 h. However, the current efficiency was rather small. The films which are obtained by electropolymerization of the pyrrole-linked rhodium complexes do not swell. Therefore, the reaction between the substrate, for example NAD+, and the reduced redox catalyst mostly takes place at the film/solution interface. To obtain a water-swellable film, which allows the easy penetration of the substrate into the film and thus renders the reaction layer larger, we used a different approach. Water-soluble copolymers of substituted vinylbipyridine rhodium complexes with N-vinylpyrrolidone, like 11 and 12, were synthesized chemically and then fixed to the surface of a graphite electrode by /-irradiation. The polymer films obtained swell very well in aqueous... 

Terpyridine ligands are known to form mono- and Ins-complexes with a wide variety of transition metal ions [321]. The stability constants and the kinetics of formation of these different complexes strongly depend on the nature of the used metal ions [322], In this respect, Rum is known to form a very stable mono-complex with one terpyridine ligand, while Ru11 only forms a stable bzs-complex with two terpyridine ligands [323]. 

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... 

The most important synthesis of 4,4 -bipyridine involves the reaction of sodium on pyridine. This reaction was discovered as long ago as 1870, although the product was not deduced to be 4,4 -bipyridine until later. " 4,4 -Bipyridine is the predominant isomer formed, although varying amounts of other isomeric bipyridines, especially 2,2 -bipyridine and 2,4 -bipyridine, may be formed, depending on the reaction conditions. The reaction involves formation of the sodium derivative of pyridine, which is formulated as the radical 67. It then couples predominantly in the 4 positions to afford 68, which with water hydrolyzes to l,T,4,4 -tetrahydro-4,4 -bipyridine. Facile oxidation then gives 4,4 -bipyridine. ° If the reaction is carried out at the temperature of boiling pyridine (IIS C) instead of at lower temperatures, the proportion of bipyridines other than 4,4 -bipyridine increases, and some terpyridines may be formed as vvell. Oxidants... 

Dale Margerum Ralph Wilkins has mentioned the interesting effect of terpyridine on the subsequent substitution reaction of the nickel complex. I would like to discuss this point—namely the effect of coordination of other ligands on the rate of substitution of the remaining coordinated water. However, before proceeding we should first focus attention on the main point of this paper-which is that a tremendous amount of kinetic data for the rate of formation of all kinds of metal complexes can be correlated with the rate of water substitution of the simple aquo metal ion. This also means that dissociation rate constants of metal complexes can be predicted from the stability constants of the complexes and the rate constant of water exchange. The data from the paper are so convincing that we can proceed to other points of discussion. 

Marcus theory (15) has been applied to the study of the reductions of the jU,2-superoxo complexes [Co2(NH3)8(/u.2-02)(/i2-NH2)]4+ and [Co2(NH3)10(ju.2-O2)]6+ with the well-characterized outer-sphere reagents [Co(bipy)3]2+, [Co(phen)3]2+, and [Co(terpy)2]2+, where bipy = 2,2 -bipyridine, phen = 1,10-phenanthroline, and terpy = 2,2 6, 2"-terpyridine (16a). The kinetics of these reactions could be adequately described using a simple outer-sphere pathway, as predicted by Marcus theory. However, the differences in reactivity between the mono-bridged and di-bridged systems do not appear to be explicable in purely structural terms. Rather, the reactivity differences appear to be caused by charge-dependent effects during the formation of the precursor complex. Some of the values for reduction potentials reported earlier for these species (16a) have been revised and corrected by later work (16b). 

The present approach to terpyridine is a two-step procedure based on a variation of the Potts strategy.11 In this sequence, the 1,5-enedione formation is accompanied by the loss of dimethyl amine and the ring closure gives terpyridine directly, thus avoiding both drawbacks of the Potts method. The synthesis of the intermediate enaminone (1) has been previously reported.12... 

Dimethylaminomethylene derivatives, usually obtained by condensation of the dimethyl acetal or diethyl acetal of dimethylformamide with an active methylene group, can react with carbanions. This results in various heterocyclization reactions including formation of the pyridine ring (91TL1999 95S557). Thus, enamine 176 and the 2-acetylpyridone anion give 2,2 6, 2"-terpyridine (177) (91TL1999). 

We fabricated the modified ITO electrodes4 by a combination of SAM formation with a terpyridine derivative and stepwise metal-terpyridine coordination reactions in a similar manner as that described in the previous section (Fig. II).11,13 A cleaned ITO was immersed in a 0.1 M solution of 4-[2,2 6, 2"-terpyridin]-4 -yl-benzoic acid (tpy-BzA) in chloroform for 12 h to anchor the carboxyl group to ITO. Subsequently, the modified ITO was immersed in an aqueous solution of 0.1 M CoCl2, Fe(BF4)2 or Zn(BF4)2 for 2—3 h to form metal-terpyridine coordination reactions. Finally, the metal-coordinated ITO was immersed in a 0.1 M acetonitrile solution of a terpyridine-functionalized porphyrin, tpy-ZnTPP, providing the target molecular wires, [M-ZnTPP], on electrodes (Fig. 11). In addition, a cleaned ITO was immersed in a 0.1 M ethanol solution of carboxylate-functionalized porphyrin, C10ZnTPP, to afford a modified ITO as a reference. 

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