Tren-based cryptands

Severin and coworkers reported (146) the reaction of tris(2-aminoethyl)amine and 4-formylphenylboronic acid with penta-erythritol to give, via multicomponent assembly, the boronic acid based macrobicyclic cage 35 (Fig. 25). The cage has the form of an ellipsoid with a diameter of 20.5 A and binds two Cud) ions in a fashion similar to the smaller tren-based cryptands. The reversible formation of boronic esters has also been employed to build other hollow structures such as nanotubes (147) and porous covalent organic frameworks (148,149). 

Synthesis of [Cu2L(CI04)4] L is a Schiff Base Cryptand Derived from the Direct 2+3 Cyclocondensation of fr/s(2-aminoethyl)amine (tren) and 2,6-b/s[formylphenoxymethyl]pyridine (bfpp) [130f]... 

Among macrocyclic tren-based reduced forms of Schiff bases, the polyamine-/amide-based cryptands represent an interesting class of ligands for anion binding as they can efficiently form ditopic and tritopic cascade complexes on binding of halide ions. Octaaminocryptands, derived from Schiff base condensations between amines and aromatic or heterocyclic dialdehydes, followed by simple reductions of the resulting imines to amines, can also form... 

Bowman-James and co-workers have designed polyamide cryptand-type systems based on triamines, such as tren (e.g. 14) and trpn (e.g. 15), and shown that they bind anions [23]. The crystal structure of the hydrochloric acid and fluoride complexes of 14 reveal that the anions are encapsulated within the cavity of the amidocryptand and boxmd to the six-amide NH groups. In contrast the hydrochloric acid structure of the expanded trpn-based amidocryptand 15 shows the encapsulation of two chloride anions within the cryptand, bridged by a water molecule. Each chloride is boimd to the water molecule as well as a protonated bridgehead amine and two hydrogen bonds from the amides groups. 

Successful anion complexation was also achieved with larger macrobicyclic ligands. Thus, the macrobicycle 17 (Fig. 17). SI binds halide anions and the linear triatomic azide anion with a very high stability constant. The x-ray structure revealed an efficient shape and size complementarity between N3 and the cavity. A whole series of polyazacryptands was obtained in high yields by a simple Schiff base [2 + 3] condensation between the triaminotriethylamine (tren) and various dicarboxalde-hydes. The hexaimine macrobicycles prepared by this way lead, after reduction, to the polyaza cryptands, which in... 

The large cavity of cryptand 17 allows another approach to anion coordination, the "cascade anion binding. " In a first step, the ligand binds by its tren subunits two Cu(II) cations. In a secorui step, the axial vacant hollow between the two alrecufy bound Cu(IT) cations will allow the binding of cn anion. An early example was based on computer analysis of potentiometric titrations data, and the efficientbinding of the chloride anion by the dicopper complex of 1 was postulated. Many other bis-tren-type figands were studied, and the cascade binding of anions such as Br, OH, N3, WCO. etc. was demonstrated. Many x-ray structures confirm the location of the anions between the various meted cations. ... 

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