Supramolecular Pseudorotaxane Polymers from Biscryptands and Bisparaquats.

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 × 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.

Pseudocryptand Hosts for Paraquats and Diquats.

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.

High-Yielding Syntheses of Crown Ether-Based Pyridyl Cryptands.

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.

The Long and the Short of It: Regiospecific Syntheses of Isomers of Dicarbomethoxydibenzo-27-crown-9 and Binding Abilities of Their Pyridyl Cryptands.

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.