Building a Simple Metal Complex

We are now ready to begin with the tutorial lessons. We will start by building and optimizing a simple metal complex. 

Once an alkyne moiety is introduced into a peptide, e.g., as propargyl glycine (Pgl) in place of a simple glycine in Enk, it can of course be used directly for complexation to a metal complex. Along those lines, we have reacted Co2(CO)g with the peptide Ac-Tyr-Gly-Pgl-Phe-Leu-NH2, to yield the Co2(CO)6 complexed to the Pgl alkyne side chain [32]. In a real SPPS scheme with a pre-formed metal-alkyne complex, the amino acid building block [Tp WI(CO)(ri2-Fmoc-Pgl-OH)] was incorporated to yield the side-chain substituted Enk derivative H-Tyr-Gly-[Tp W(I)(CO)(r 2-Pgl)]-Phe-Leu-OH (Tp tris(3,5-dimethylpyrazolyl)-borate) [44]. 

In the structures, introduced so far, an O4 rhomb or O5 patterns turned out to be ideal building blocks for carbohydrate-metal complexes. The most important monosaccharide, D-glucose, in any of its hemiacetal forms does not exceed the simple 02 diol pattern ( a consequence is the epimerization reaction of glucose to 8-mannofuranose in the presence of trivalent metal ions). 

Tschierske and coworkers reported on new complex liquid crystalline phases of polyphilic block molecules or their metal complex [91-93]. These triblock rod-coil molecules consist of a rod-like p-terphenylene unit, and two hydrophobic alkyl chains at both ends of the rod, and oligo(ethylene glycol) with a terminal carbohydrate unit at a lateral position of the rod [94]. Depending on the size of the hydrophilic and hydrophobic segments, a series of unusual liquid crystalline phases were detected (Fig. 18). When the carbohydrate unit is directly conjugated to the rod building block, a simple smectic (Sa) phase was observed. In this liquid crystalline phase, the molecules are... 

In this context, however, asymmetric transformations with chiral metal complexes or enzymes are particularly important. The demand for enantiopure building blocks in the fine chemical and pharmaceutical industries is still hampered by simple asymmetric processes which can be scaled up, as well as by the stability, recyclability, and hence the price of most chiral catalysts (refer also to the chapter by K.-U. Schoning in this volume). Immobilization of effective and robust catalytic systems and their application in continuous flow reactors is regarded as a key for success in this field. 

Like all simple triazolopyridines, bitriazolopyridines 76 react with electrophiles to produce 2,2 -bipyridines 118 (Scheme 24). With these reactions a general route to 2,2 -bipyridines has been discovered with a variety of substituents in the 6 and 6 positions (97T8257). These compounds have use in supramolecular chemistry because of their great complexing power for metal ions and, in particular, 2,2 -disubstituted-6,6 -bipyridines are useful building blocks for oligobipyridines, which spontaneously form helical metal complexes (92T8451). 

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