Tetraimine Schiff base macrocycle

Silver(I) complexes with macrocyclic nitrogen ligands are also very numerous. Mono- or homodi-nuclear silver-containing molecular clefts can be synthesized from the cyclocondensation of functionalized alkanediamines or triamines with 2,6-diacetylpyridine, pyridine-2,6-dicarbalde-hyde, thiophene-2,5-dicarbaldehyde, furan-2,5-dicarbaldehyde, or pyrrole-2,5-dicarbaldehyde in the presence of silver(I).486 97 The clefts are derived from bibracchial tetraimine Schiff base macrocycles and have been used, via transmetallation reactions, to complex other metal centers. The incorporation of a range of functionalized triamines has provided the conformational flexibility to vary the homodinuclear intermetallic separation from ca. 3 A to an excess of 6 A, and also to incorporate anions as intermetallic spacers. Some examples of the silver(I) complexes obtained are shown in Figure 5. 

ABSTRACT. The application of tetraimine Schiff base macrocycles as ligands in the modelling of di- and trinuclear copper(I) and copper(II) biosites and dinuclear manganese(II) biosites is discussed. 

By varying the nature of the heterocyclic dicarbonyl ( head unit ) and the l,n-diamine ( lateral unit ), a wide range of dinucleating tetraimine Schiff base macrocycles can be synthesised. 

According to the structure determination results, it is presumed that the reversion from the carbinolamine form to the tetraimine one exists probably because of the optimal cation-cavity criteria and the fact that the samarium ion can be accommodated by either form of the two macrocycles. Carbinolamine, acting as the intermediate of the tetraimine Schiff base 27, is the kinetically favored product. In contrast, the latter species is the thermodynamically favored product. On dissolution and recrystallization in water, a higher temperature is reached than in the original reaction in alcohol, which facilitates completion of the reaction. Furthermore,... 

Thiophene aldehydes have been used earlier for the construction of macrocyclic Schiff bases <81CC628>. An example is the synthesis of the macrocyclic tetraimine Schiff base (479) from thiophene 2,5-dicarbaldehyde and l,3-diamino-2-hydroxypropane <87JCS(D)219>. The synthesis does not involve use of a metal template. An interesting extension is the synthesis of the macrocyclic Schiff base (481) containing four thiophene units from the dialdehyde (480) <89BCJ1346>. The condensation is achieved at room temperature in CHCI3. 

Other template cyclizations. In another Schiff-base template reaction, 1,3-diaminopropane monohydrochloride was reacted with biacetyl in methanol in the presence of Ni(n) to yield the nickel complex of the corresponding cyclic tetraimine - see [2.16] (Jackels et al., 1972). The success of the procedure illustrated is quite dependent on the reaction conditions employed. Attempts to isolate the metal-free macrocycle were unsuccessful - this once again emphasizes the stabilizing role of the metal... 

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