Cationic complexes macrocycles

The first structurally characterized example of a platinum(II) derivative containing a saturated tetraamine macrocycle, 6,13-dimethyl-l,4,8,ll-tetraazacyclotetradecane-6,13-diamine has been reported (80).251 The species crystallizes as the colorless tetra-cationic complex from dilute HC104 solution by slow evaporation, where the two pendant primary amines are protonated. Other macrocyclic tetraamine complexes including [Pt([14]aneN4)]Cl2 have also been described.252... 

Intramolecularity in lariat ether complexation was demonstrated in three ways. First, when solution cation binding constants were determined. Kg was shown to be independent of cation and macrocycle concentrations (within certain limits). The efficacy of complexation of a single cation by two macrorings [(ML2) complex formation] should be concentration dependent. Second, ammonium cation binding constants were determined for the series (see above) of monoaza-15-crown-5 and -18-crown-6 compounds having (CH2CH20)jiClH3 (n 0 to 8) sidearms (31). 

Anion effects have been observed especially in relation to dissolution of the cation complexes in media of low polarity. Soft organic and inorganic anions (phenates, thiocyanate, permanganate etc) generally allow ready dissolution the pier ate anion has been much used (62, 66). The interaction between the anion and the complexed cation may affect the stability of the complex. Ion pairing may occur when the anion can contact the complexed cation, as in the case of macrocyclic complexes, where approach of the anion from top and bottom is possible. This is observed in the RbNCS complex of IS, but not in its NaNCS complex, as shown by the crystal structure data (100). With bromide as anion both a complexed ion pair and a complexed sodium cation are found in the solid state for (15, NaBr) (118). 

Impetus was given to work in the field of selective cation complex-ation by the observation of Moore and Pressman (5) in 1964 that the macrocyclic antibiotic valinomycin is capable of actively transporting K+ across mitochondrial membranes. This observation has been confirmed and extended to numerous macrocyclic compounds. There is now an extensive literature on the selective complexation and transport of alkali metal ions by various macrocyclic compounds (e.g., valinomycin, mo-nactin, etc.) (2). From solution spectral (6) and crystal X-ray (7) studies we know that in these complexes the alkali metal cation is situated in the center of the inwardly oriented oxygen donor atoms. Similar results are found from X-ray studies of cyclic polyether complexes of alkali metal ions (8) and barium ion (9). These metal macrocyclic compound systems are especially noteworthy since they involve some of the few cases where alkali metal ions participate in complex ion formation in aqueous solution. 

Stability constants, from which AG° values are calculated, provide a direct measure of the extent of complexing in solution, and these values have been used to determine cation selectivity by macrocyclic compounds. Several of the methods commonly used to determine log K values cannot be used with many of these systems. Thus, procedures based on change in hydrogen ion concentration (pH titration, hydrogen electrode, etc.) cannot be used in those cases where the ligand is uncharged and its concentration is not pH dependent. Spectral methods generally have not been used because of the usual lack of favorable absorption characteristics by the compounds, cations or cation-complexes in the cases studied. 

The template condensation of 2,3-butanedione dihydrazone with aldehydes or ketones affords a variety of octaazabis(a-diimine) macrocyclic complexes of nickel(II), according to the Scheme 48.2655 NH deprotonation with py or Et3N of the aforementioned cationic complexes leads to neutral NiL species. 

In the case of cationic complexes with unsaturated macrocycles two molecules of nucleophile, such as ammonia, amines and alkoxides, add to carbon atoms of two inline groups. For example, the reaction of [Ni(Bzo[16]octaeneN4)](C104)2 (Table 106) with sodium methoxide or ethoxide yields the compounds (395),2860 while with secondary amines and diamines complexes of type (396) are obtained.28 1 The reaction of (396) with acetone at room temperature yields complex (397) where the enolate anion of acetone, MeC(0)CH2, replaces the diethylamide group (Scheme 58). 2862 The addition of molecules such as bis(2-hydroxyethyl)methylamine and bis(2-hydroxyethyl) sulfide, HOCH2CH2YCH2CH2OH (Y = NMe, S) results in the formation of derivatives which possess one more coordination site just above the plane of the macrocyclic donors (398).2863... 

Fig. 12. Electron-cation coupled transport a redox-driven electron-cation symport consisting of an electron carrier (nickel complex) and a selective cation carrier (macrocyclic polyether). RED, potassium dithionite OX, Na3[Fe(CNft)].

Light-driven (electron, cation) symport occurs when combining this system with the (nickel complex, macrocycle) process described above [6.62]. Photocontrol of ion extraction and transport has been realized with macrocyclic or acyclic ligands (containing, for instance, azo or spirobenzopyran groups) that undergo a reversible... 

The bonding of an ion, such as Na+, with a polar molecule, such as water, is an example of an ion-dipole interaction, which range in strength from ca. 50 - 200 kj mol-1. This kind of bonding is seen both in the solid state and in solution. A supramolecular analogue is readily apparent in the structures of the complexes of alkali metal cations with macrocyclic (large ring) ethers termed crown ethers... 

Complexation of inorganic cations such as alkaline or alkaline earth metals by macrocyclic polyethers produces large, lipophilic cationic metal-macrocycle complexes that are readily soluble in nonpolar solvents such as benzene, toluene and haloalkanes. In order to maintain charge balance, the cationic complex has an associated counter anion. In an immiscible two-phase liquid system, such as a mixture of chloroform and water, the anion is necessarily pulled into the organic phase as the cationic complex crosses the phase boundary. A simple illustration of this principle is obtained by addition of a chloroform solution of [18]crown-6 to an aqueous solution of potassium picrate (potassium 2,4,6-trinitrophenolate). The yellow colour of the picrate anion is transported rapidly into the contiguous (physically in contact) chloroform phase upon agitation (Figure 3.43). 

Atwood, J. L., Cation complexation by calixarenes . in Cation Complexation by Macrocycles, Inoue, Y., Gokel, G., eds. Dekker New York, 1991. 

Pedersen s reports of the compounds he called crown ethers (Pedersen, 1967) began a world wide synthetic effort to prepare novel macrocycles, to define the limits of crown ether structure, and to assess the range of their biological and chemical properties. Among the latter, great effort was expended to define and understand cation complexation by these remarkable molecules. On the biological side, the toxic effects of crown ethers to cell lines and animals were assayed to understand their inherent safety or danger and the... 

Gokel, G. W., Cram, D. J., (1973) Molecular complexes of arenediazonium and benzoyl cations by macrocyclic polyethers Chem. Commun. 481-482. 

Lamb, J. D. and Drake, P. A. (1989) Chemically-Suppressed Anion Chromatography Based On Macrocycle-Cation Complexation, J. Chromatogr. 482, 367-380. ... 

The first observation of the NMR spectrum of Na- in a metal solution without added cation-complexing agents has recently been reported (65a). The rationale behind this observation was that the solvent HMPA by itself appeared to fulfill many of the requirements generally sought from macrocyclic complexing agents high solubility via cation complexation, stability to electron reduction, weak anion solvation, etc. The NMR spectrum of Na- in fluid Na-HMPA solutions, shown in Fig. 26, exhibits precisely the same chemical shift as that observed for Na-in solutions of Na in anhydrous methylamine and ethylamine in the presence of 2,2,2-cryptand. The metal anion here is truly "gas-like in... 

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