Boronic crown-ether containing

Simultaneous complexation of anions and cations, in a similar way to that reported for 15-crown-5 uranyl salene complexes, has been observed in the 21-membered ring boronate crown ether 40. Ligand 40 is capable of dissolving stoichiometric amounts of KF in dichloromethane at room temperature to give the KF adduct shown at Figure 13. The fluoride ion is bound to the boron atom out of the plane of the crown ether, which contains the ion. Ligand 40 fails to dissolve... 

Tschierske developed a variety of molecules containing a p-terphenyl unit as backbone equipped with two terminal decyloxy chains and laterally attached crown ethers of different sizes [51-53]. The synthesis was straightforward starting from methyl-2,5-dibromobenzoate 30 that was coupled with [4-(decyloxy)phenyl]boronic acid 31 in a subsequent Pd°-catalyzed Suzuki reaction. The 2-hydroxymethyl crown ethers 32 were attached in the last step (Scheme 18) to yield mesogenic 33. 

For less activated aromatic systems (those without a nitro substituent), the halogcn-ex-changc reaction has been investigated with potassium fluoride in a variety of polar aprotic solvents in the presence or absence of a catalyst (see Table 13). Many different types of catalysts have been investigated these include crown ethers, quaternary ammonium salts, 3,164 pjjos-phonium salts, aminophosphonium salts, compounds containing a phosphorus and an amino function, and inorganic fluorides of boron, aluminum, tin, phosphorus, titanium and zirconium. Different forms of potassium fluoride have been used these include spray-dried potassium fluoride, freeze-dried potassium fluoride, potassium fluoride recryslal-lized from methanol, and potassium fluoride dispersed on caleium fluoride. ... 

Organoboron rings containing three or more boron centers may be viewed as inverse crown ethers. DFT calculations suggest that triboramacrocycle (180), in which the boron centers are coimected via ethylene bridges, effectively coordinates halide, hydride and methide ions (equation Good selectivity for fluoride over other... 

The incorporation of two aryl bridgeheads, both linked in turn through the 2,6-substitution of a pyridine nucleus has provided an intermediate which has been converted to a crown ether. Thus, 2,6-bis(2, 6 -dimethoxyphenyl)pyridine after demethylation with boron tribromide or hydrogen bromide in 65% yield was reacted in dimethylsulphoxide containing potassium carbonate with the a,o)-diiodo derivative of triethylene glycol to afford a crown ether system in 22% yield (ref. 199). 

Gagn6 et al. developed polymer active sites that additionally contained a receptor (recognition sites) displayed in the outer sphere of the metal center (reactive site). The Suzuki reaction of /)-bromoanisole with phenyl boronic acid and the allylation of dimethyl malonate with allyl acetate were both chosen to assess the presence and/or effect of the crown-ether in crown-ether-molecular imprinting polymer-palladium complex. The results showed that molecular imprinting can be used to functionalize the second-coordination sphere of a transition metal complex and subsequently affect its catalytic behavior. 

Reetz et al. have published a heterotopic receptor, which in addition to a crown ether moiety for complexation of potassium cations, contains a g-bonded Lewis acidic boron center that is able to form a tetracoordinated adduct with anions and with a selectivity for fluoride anions [ref 31]. Novel artificial polytopic receptors for binding of zwitterionic aminocarboxylates have been also published [ref 32]. 

Two new chiral macrocyclic compounds containing both a crown ether and a boronic ester were prepared from methyl 4,6-0-isopropylidene-OC-D-mannopyranoside 4 as shown in Figure. 

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