4,4 -bipyridyl linker

An interesting feature of the binding of a double-ended substrate into a cyclodextrin dimer is that the substrate is held right on top of the linker group. If that linker carries a catalytic function, one can imagine very effective catalysis of reactions at the middle of the substrate. We have examined a number of such processes, and have achieved some very large catalyses in appropriate cases. Here we will describe catalysis by a cyclodextrin dimer 30 carrying a bipyridyl linker. This linker can bind... 

Figure 1.6 Reactions in which cyclodextrins combine with metal ions in catalysis in water. Compound 10 was the first species described as an artificial enzyme in the literature. Compound 11 binds both ends of a substrate such as 12 and catalyzes its hydrolysis with a metal ion bound to the bipyridyl linker of 11.

Beer and coworkers have modified their approach by derivatizing the upper rim of calix[4]arene with two (48, Tos = tosylate) and four (49) Ru(II) tris-bipyridyl reporter sites. The amide linkers of 48 and 49 form a hydrogen-bonding cleft for anion occupation. A preliminary report [385] indicates that MLCT luminescence from the Ru(II) centers is sensitive to anion association. 

Pyridine complexes can show analogous hindered rotation to that observed with metal-aryl complexes. This has been observed for over SOyears, but recent interest in supramolecular chemistry, particularly by Fujita and Stang, wherein bipyridyls have been used as linkers has spurred renewed interest in the phenomenon. Several articles on dynamics provide leading references for applications of EXSY and other DNMR methods in these systems. BINAP complexes with picolines and methyl-substituted isoquinolines, which show syn and anti isomerism, have been investigated, for example, (48), (49), and (50). ... 

An extension of this work has resulted in the synthesis of related 6,6-disubsti-tuted (bipyridyl) ligand derivatives containing pyromellitimide spacers connected with propynyl, butynyl and propynyloxy linkers.The first of these ligands was shown to yield a chiral di-zinc(II) cationic complex of type [Zn2L2] . This species is stabilised by the presence of an aromatic guest p- or o-dimethoxybenzene) in its cavity. Related dinuclear species were also shown to form with cadmium(II) and nickel(II). 

Cu(II) ions have been used to assemble tetra- and octavalent V-acetyl galactosy-lamide dendrons (Fig. 35). The carbohydrate epitopes were first attached to a bipyridyl system using linker of different length. Tetracoordination of the Cu(II) core produced the glycodendrimers which were characterized using proton and carbon NMR, MALDI-Tof mass spectrometry, and UV-VIS spectroscopy [233],... 

The p-bu -calix[4]arene-linked mono and di-trisbipyridylruthenium° complexes 151, 152 formed by the reactions of cis-Ru (bipy)2Q2 and lower rim conjugates of p-bu -calix[4]arene and 2,2 -bipyridyl unit(s) linked at 5 -position(s) through methylene linker(s), have free OH groups acting as add-base sites. By operation of an intramolecular photoinduced electron transfer process, these complexes showed luminescent pH sensor action (94JC S(CC)185). 

Twistophanes 10 and 11 represent a new class of cyclophanes that recently emerged as the follow-up compounds to the endobasic host 9 first prepared by Baxter. The cyclic structures comprise substituted 2,2 -bipyridyl groups linked via acetylinic linkers, and they are primarily developed as sensors for metal ions. For both... 

We have used this plan - cyclodextrin binding in water solution, but catalysis by metal ions - in many subsequent studies. For example, we created a dimer 11 of cyclodextrin with a bipyridyl group in the linker, which would bind metal ions. We then examined its use with Cu + as a catalyst for hydrolyzing esters such as 12 that could doubly bind into both cyclodextrin groups in water. We saw a 220,000-fold acceleration of the hydrolysis of such a doubly binding ester. As expected, the product fi-agments could not doubly bind, so they did not inhibit the catalytic hydrolysis process. 

In our pursuit of metal-coordinating supramolecular polymers, we prepared compound 8 so that it has a bipyridyl (bipy) linker coimecting two PDl moieties. One of the consequences of having bipy is the completely flat geometry of the... 

Choe and coworkers provided the first examples of this PSM process. They demonstrated that the porphyrin-based MOF [Zn2 Zn(L ) (L )] reacts with 4,4 -bipyridyl to form [Zn2 Zn(L " ) (bpy)]. The transformation involves a decrease between layers from 21.2 to 12.8 A, consistent with the shorter length of the bpy linker. 

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