Lariat ethers bibracchial

Cation-Binding Properties of Crown Ethers, Lariat Ethers, Bibracchial Lariat Ethers, and Poly(ethylene glycols) as Potential Phase-Transfer Catalysts... 

Alcohol sidearms, bibracchial lariat ethers, 34 Alkenes... 

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. 

Fig. 4.38. Stability constants in water at 298 K and = 0.1 M, for lanthanide complexes with the (2.2.1) cryptand and the bibracchial lariat ethers (2.1)DA and (2.2)DA. From data reported by J.-C.G. Biinzli, in Handbook on the Physics and Chemistry of Rare Earths, eds K.A. Gschneidner Jr., L. Eyring, Vol. 9, Ch. 60, North Holland,...

The two center structures show the complex that forms between iV,iV -bis(2-phenylethyl)-4,13-diaza-18-crown-6 and KI <2000PNAS6271>. The K+ ion is bound in the center of the macroring, as expected for any 18-crown-6 macrocycle. The twin sidearms of the bibracchial lariat ether turn inward in this complex and the arenes serve as apical donors. The top center structure shows the symmetrically bound cation and illustrates that the iodide anion is excluded from the cation s solvation sphere. The bottom center structure shows the superimposition of the two benzene rings upon each other and upon the K+ ion. Note in the bottom center structure that the iodide anion is not illustrated. The ideal sandwich of arene-cation-arene confirms the cation-pi interaction between benzene and K+. 

Another control experiment was run to further confirm the significance of the cation-pi interaction in these bibracchial lariat ether model complexes. In this case, a diaza-18-crown-6 derivative was prepared in which a 2-phenylethyl pi-donor sidearm was attached to one nitrogen and a 2-methoxyethyl sigma donor was attached to the other <2002CC1808>. The structure is illustrated as 14, above. The solid-state structure of the 14 KI complex showed the typical apical solvation of the ring bound cation. In this case, however, one apex was solvated in the pi-fashion (benzene) and the other by the oxygen sigma donor. 

Gonzlez-Lorenzo, M., Platas-lglesias, C., Avecilla, E, et al. (2005) Structural and photophysical properties of lathanide(III) complexes with a novel octadentate iminophenolate bibracchial lariat ether. Inorganic Chemistry, 44, 4254. 

Platas, C., Avecilla, R, de Bias, A., et al. (2001) A Schiff-base bibracchial lariat ether selective receptor for lanthanide(lll) ions. Journal of the Chemical Society, Dalton Transactions, 1699. 

Table III. Na+, K+, and Ca2+ Binding for 15- and 18-Membered Ring Bibracchial Lariat Ethers...

Gatto, V.J. Gokel. G.W. Syntheses of ealeium-selective, substituted diazacrown ethers A novel, one-step formation of bibracchial lariat ethers (BiBLES). J. Am. Chem. Soc. 1984, 106, 8240-8244. 

Gatto, V.J. Arnold, K.A. Viscariello. A.M. Miller. S.R. Gokel, G.W. Novel synthetic access to 15- and 18-membered ring diaza-bibracchial lariat ethers (BiBLEs) and a study of sidearm-macroring cooperativity in cation binding. Tetrahedron Lett. 1986, 327-330. 

Diaza[18]crown-6 (2.20) can also be readily functionalised with two side arms, instead of just one as in 2.21, to form double lariat ethers termed bibracchial lariat ethers (BiBLEs), such as 2.24. This modification results in the possibility of the side arms covering both faces of the macrocycle (Figure 2.6(a)). A particularly striking example is the complexation of sodium in a BiBLE that contains two thymine groups as the side arms (Figure 2.6(b)). 

Figure 2.6 (a) Schematic showing a guest species being bound by two pendant side arms in a bibracchial lariat ether (BiBLE) and (b) complexation of sodium in the BiBLE 2.24 which contains two thymine groups as the side arms. 

Table 2.6 Stability constants for bibracchial lariat ethers...

Two-armed nitrogen pivot systems, termed bibracchial lariat ethers (BiBLEs), have recently been synthesized in one-step reactions (79). (Scheme 6). Table 2.6 reports the stability constants of a number of these compounds for the Na", and Ca guest cations. It can be seen that polar donor groups like ester carbonyl in the sidearms strongly favour Ca over either Na" or but less polar groups like ethers favour... 

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