Schiff cryptands

Similarly, by Schiff-base condensation reactions have been used to generate free cryptands from triamines and dicarbonyls in [2+3] condensation mode. These ligands react with silver(I) compounds to give dinuclear or trinuclear macrocyclic compounds where Ag Ag interactions may be present. Thus, with a small azacryptand a dinuclear complex with a short Ag- Ag distance (55) is found.498 With bigger azacryptand ligands also dinuclear complexes as (56) are achieved but without silver-silver interaction. 65,499-501 A heterobinuclear Ag1—Cu1 cryptate has also been... 

The synthetic routes may often involve template directed condensations, a widely used reaction being the (carbonyl + amine) to imine condensation that efficiently leads to a variety of Schiff-base macrocycles [2.58-2.60, A.7, A.14], macrobicyclic cryptands [2.61-2.63] and lacunar cyclidene ligands [2.60, 2.64]. 

Schiff base macrocycles and phthalocyanines are readily prepared and pre-date crown ethers and cryptands but are more suitable for binding transition metals or softer main group ions. 

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]... 

The three Schiff-base bibracchial lariat ethers H2l7a-c derivatives have been designed for their ability to form a cryptand-like cavity upon reaction with Lnm ions, the size of which can be tuned by varying the number of -CH2-CH2-O- units in the macrocycle. The two 2-salicylaldiminobenzyl pendant arms fold in such a way that jt-jt interactions between aromatic rings result in the formation of a cryptand-like cavity, as demonstrated by the X-ray structure of the Cem complex with 17b depicted on fig. 25 (Gonzales-Lorenzo et al., 2003). The triplet state of the di-anionic receptor is located at 18750 cm-1 (0-phonon component measured on the Gd111 complex) so that sensitization of the NIR luminescence is not optimum nevertheless, Ndm emission could be detected. 

Gonzlez-Lorenzo, M., Platas-lglesias, C., Avecilla, E, et al. (2003) A Schiff-base bibracchial lariat ether forming a cryptand-like cavity for lanthanide ions. Inorganic Chemistry, 42, 6946. 

A very different type of nitrogen-bridged expanded porphyrin is defined by two cryptand-like species recently reported by Sessler and coworkers.The first of these, the tripyrrane-strapped porphyrin 9.130, was prepared via the Schiff base-type condensation of one equivalent of diformyltripyrrane 9.128 with the a,P,a,P-atropisomer of tetrakis(2-aminophenyl)porphyrin 9.129 (Scheme 9.2.9). When two equivalents of tripyrrane 9.128 are used, the doubly strapped porphyrin 9.131 can be isolated. Both of these systems can be consistently prepared in 3CM5% yields. 

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 reaction of the diprotonated cryptand (16) with Cu(CH3CN)4Bp4 in methanol gave a dinuclear copper(I) complex (18) of the neutral cryptand. The X-ray crystal structure of this complex (Fig. 12b) shows that both the integrity of the cryptand and the unusual trans-trans conformations of the dicarbimine functions found in the protonated ciwptand are retained in the structure of the complex. The Cu(I)...Cu(I) separation is 6.25A. This copper separation is well in excess of that reported, 3.04A, for the dicopper(I) complex, [L Cu2](C104)2, in which is the [3+2] Schiff base cryptand derived from 2,6-... 

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... 

Condensation of tripodal trialdehydes L1024 or L1025 (Eq. 4.39) with 1,2-diaminobenzene in the molar ratio 2 3 in the presence of Cs as template, followed by reduction of the resulting Schiff bases with NaBH4, produces the cryptands L1026 and L1027 in 35% and 30% yield, respectively (Eq. 4.40) [146]. Note that in the absence of Cs a mixture of unidentifiable composition is formed. 

Reaction of HL1028 with tris(2-aminoethyl)amine (L685) in acetonitrile-methanol (25 1) affords the macrobicyclic Schiff base H3LIO29 in 65% yield [147]. Reduction of the latter in methanol gives the cryptand H3LIO3O (Eq. 4.41). 

Drew MGB, Marrs D, Hunter J, Nelson J (1992) Divergent and convergent forms of a new Schiff-base cryptand X-ray crystallographic and molecular mechanics investigations J Chem Soc Dalton Trans 11-18... 

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