Search

Abstract: Two new cryptands, 2 and 4, were prepared from bis(m‐phenylene)‐32‐crown‐10 (BMP32) 5,5'‐diacid chloride and dibenzo‐30‐crown‐10 (DB30) 4,4'‐diacid chloride, respectively, by reaction with pyridine‐2,6‐dimethanol. The resultant cryptands 2 and 4 have the ester moieties reversed from the previously reported isomers, 1 and 3. These “reverse” cryptands display lower association constants with viologen derivatives than the original cryptands; this is rationalized by the conjugation of the ester moieties with the aromatic rings, which reduces their electron‐donating properties and offsets the increased basicity of the pyridyl nitrogen atoms. The crystal structure of the BMP32‐based cryptand 2 indeed confirms the coplanarity of the ester and aromatic moieties and indicates that, as a result, the available cavity is quite small and that the pyridyl nitrogen atom points away from the cavity. [ABSTRACT FROM AUTHOR]

Five new bis(dibenzo-30-crown-10-based cryptand)s were synthesized, two of which (16 and 17) had long (12-atom), flexible spacers that led to cooperative complexation of dibenzyl paraquat TFSI (Kave = 4.36 x 105 M-1 for 17•2b). Self-assembly of 16 and 17 with bisparaquats with similar spacers (18, 21, and 23) led to high molecular weight supramolecular pseudorotaxane polymers in solution. Continuous, flexible fibers were drawn from concentrated solutions. 17 with C10-linked bisparaquat 23 in dichloromethane (DCM) produced a log-log viscosity vs concentration plot with a limiting slope of 3.55, confirming high molecular weight; at 37 mM, the degree of polymerization was estimated to be 126 and Mn = 407 kDa. These are the first truly polymeric pseudorotaxane-type AA/BB supramolecular polymers. [ABSTRACT FROM AUTHOR]

H-bonding interaction of acidic moieties (CH2OH, COOH) at the 5- and 5'-positions of bis(1,3-phenylene)-32-crown-10 (1) with di- or tritopic anions leads to enhanced formation of inclusion complexes with N,N'-dialkyl-4,4'-bipyridinium salts ("paraquats", 2); the enforced folding of the crown ethers into pseudocryptands thus leads to pseudo-pseudorotaxanes. Strikingly, in the presence of the most effective anion (trifluoroacetate, TFA), the apparent bimolecular association constants for crown-paraquat complexation increase by more than an order of magnitude and approach those for covalent cryptands derived from the crown ether. Even though they may form pseudocryptands, the picolinate, nicotinate, and isonicotinate diesters 6 of cis-(4,4')-bis(hydroxymethyl)dibenzo-30-crown-10 do not exhibit enhanced binding of either diquat or paraquat relative to the starting diol in contrast to the picolinate ester of isomeric 5,5'-bis(hydroxymethyl)bis(m-phenylene)-32-crown-10, which displayed a higher binding constant than the starting diol. The results for the analogous reverse esters 7 derived from cis-(4,4')-dicarboxydibenzo-30-crown-10 and pyridylmethanols reveal weaker complexes with diquat than the normal esters 6; however, surprisingly, two reverse esters 7 complex paraquat more strongly than isomers 6. [ABSTRACT FROM AUTHOR]

Abstract: The commonly used paraquat guest N,N′‐dimethyl‐4,4′‐bipyridinium bis(hexafluorophosphate) (7) was targeted for structural alterations to improve the binding constants with crown ethers and cryptands. The association constant was improved by one order of magnitude (to Ka = 1.00 × 106 mol L−1) with the dibenzo‐30‐crown‐10 pyridyl cryptand host 5 by changing the N‐methyl groups to benzyl and the counterions from PF6 to TFSI, that is, 11. Moreover, through addition of a p‐bromobenzyloxy moiety on the 4‐position of the pyridyl ring of cryptand 18, an association constant of Ka = 5.35 × 106 mol L−1 was achieved with paraquat 11. [ABSTRACT FROM AUTHOR]

The two isomers 6 and 9 of cis(4,4'-)-dicarbomethoxydibenzo-27-crown-9 with tri- and tetra-(ethyleneoxy) linkages transposed were synthesized regiospecifically in high yields (94 and 92%, respectively) by the Wang-Pederson-Wessels (WPW) protocol and were converted via the corresponding diols 7 and 10 to the corresponding pyridyl cryptands 3 and 4 by reaction with pyridine-2,6-dicarbonyl chloride. As expected from Corey-Pauling-Koltun (CPK) models, the cryptand with the tri(ethyleneoxy) arm para to the ester linkages, "short-armed" cryptand 3, did display a higher binding constant (Ka = 2.4 × 105 M-1) with paraquats than the analogous dibenzo-30-crown-10-based cryptand previously studied; however, the effect was only twofold. Its binding to diquat was reduced by an order of magnitude (1.5 × 105 M-1), as expected on the basis of its narrower cavity. Also as expected, the cryptand with the tetra(ethyleneoxy) arm para to the ester linkages, "long-armed" cryptand 4, possessed diminished binding with both paraquats and diquat relative to the 30-crown-based analogue; in these systems, 2:1 H:G complexes were also detected by mass spectrometry. A crystal structure is reported for 3·DQ(PF6)2. [ABSTRACT FROM AUTHOR]

Pyridinium bis(trifluoromethylsulfonyl)imide (PyTFSI)-templated syntheses of 2,6-pyridyl cryptands of cis(4,4')-dibenzo-30-crown-10 (3a), the p-bromobenzyloxy derivative 3b, bis(m-phenylene)-32-crown-10 (5), cis(4,4')-dibenzo-27S-crown-9 (7), cis(4,4')-dibenzo-27L-crown-9 (9), and cis(4,4')-dibenzo-24-crown-8 (11) are reported. Here we provide a fast (12 h), high-yielding (89%, 74%, 80%, and 62% for 3a, 3b, 5, and 9, respectively) templation method without the use of a syringe pump. The yields for 7 (19%) and 11 (26%) were lower than with the previous pseudo-high-dilution method, indicating ineffective templation in these cases. Coupled with our previously developed templated syntheses of dibenzo crown ethers, this protocol makes powerful cryptand hosts readily available in gram quantities in good yields from methyl 4(or 3)-hydroxy-3(or 4)-benzyloxybenzoate. [ABSTRACT FROM AUTHOR]

A series of alkylated isoquinoline Reissert compounds (2-acyl-1-alkyl-1,2-dihydroisoquinoline-1-nitriles) with either 3-H (3) or 3-CH3 (4) substituents was examined by ¹H, 13C, and 19F NMR spectroscopies and X-ray crystallography. In all cases the trans-amide conformation, with reference to the carbonyl oxygen and the 3-position of the isoquinoline ring, exists exclusively in the solid state, and predominates in solution. As expected the 1-alkyl groups (isopropyl, isobutyl, benzyl) are nearly pseudo-axial or axial in all cases. In N-aroyl compounds the larger ortho-aroyl substituent lies syn to the 1-alkyl moiety in nine of the 11 cases, as revealed by X-ray crystallographic studies. In solution NMR results show that atropisomerism about the Ar/CO bond is usually rapid at room temperature, but slow at -50 °C and usually favors the syn isomer. CH⋯π interactions of the 3-methyl protons of 4 with the N-aroyl moieties appear to influence the atropisomerism. [ABSTRACT FROM AUTHOR]