Bis(m-phenylene)-32-crown-10-Based Cryptands, Powerful Hosts for Paraquat Derivatives Feihe Huang,† Karen A. Switek,†,‡ Lev N. Zakharov,§,| Frank R. Fronczek,⊥ Carla Slebodnick,† Matthew Lam,§ James A. Golen,# William S. Bryant,†,X Philip E. Mason,†,∇ Arnold L. Rheingold,§,| Mehdi Ashraf-Khorassani,† and Harry W. Gibson*,† Department of Chemistry, Virginia Polytechnic Institute & State University, Blacksburg, Virginia 24061
[email protected] Received January 29, 2005
Four new bis(m-phenylene)-32-crown-10-based cryptands with different third bridges were prepared. Their complexes with paraquat derivatives were studied by proton NMR spectroscopy, mass spectrometry, and X-ray analysis. It was found that these cryptands bind paraquat derivatives very strongly. Specifically, a diester cryptand with a pyridyl nitrogen atom located at a site occupied by either water or a PF6 anion in analogous complexes exhibited the highest association constant Ka ) 5.0 × 106 M-1 in acetone with paraquat, 9000 times greater than the crown ether system. X-ray structures of this and analogous complexes demonstrate that improved complexation with this host is a consequence of preorganization, adequate ring size for occupation by the guest, and the proper location of the pyridyl N-atom for binding to the β-pyridinium hydrogens of the paraquat guests. This readily accessible cryptand is one of the most powerful hosts reported for paraquats.
Introduction Self-assembled structures are attractive to materials science for their reversibility at the molecular level and, therefore, for their ability to correct structural defects, an option unavailable for traditional, covalently bonded systems.1 However, in order for a self-assembling, noncovalent system to possess properties sufficient to compete with covalently bonded polymers, it must exhibit a strong association between its components.2 Paraquat derivatives (N,N′-dialkyl-4,4′-biyridinium salts) have * To whom correspondence should be addressed. Fax: 540-231-8517. † Virginia Polytechnic Institute & State University. ‡ Summer Undergraduate Research Participant, 1999, supported by the National Science Foundation through DMR 922487 REU. Present address: Department of Chemistry, University of Minnesota, Minneapolis, MN 55455-0431. § Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716. | Present address: Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093-0358. ⊥ Department of Chemistry, Louisiana State University, Baton Rouge, LA 70803. # Department of Chemistry and Biochemistry, University of Massachusetts Dartmouth, North Dartmouth, MA 02747. X Present address: Imerys Pigments, INC., Roswell, GA 30076. ∇ Present address: Department of Food Science, Cornell University, Ithaca, NY 14853.
been widely used as guests in supramolecular chemistry to construct numerous complexes with large crown ethers, such as bis(m-phenylene)-32-crown-10 derivatives (1) and bis(p-phenylene)-34-crown-10 derivatives.3 With the aim to prepare large supramolecular systems4 efficiently from small building blocks, we are interested in improving complexation of paraquats (2) by design of optimized hosts. Here, by synthesizing four new bis(mphenylene)-32-crown-10-based cryptands (3) and studying their complexation with paraquat derivatives, we address two questions. First, why are cryptands better hosts for paraquat derivatives than the corresponding (1) (a) Ducharme, Y.; Wuest, J. D. J. Org. Chem. 1988, 53, 57895791. (b) Kato, T.; Fre´chet, J. M. J. J. Am. Chem. Soc. 1989, 111, 85338534. (c) Hilger, C.; Dra¨ger, M.; Stadler, R. Macromolecules 1992, 25, 2498-2501. (d) Chang, Y.-L.; West, M.-A.; Fowler, F. W.; Lauher, J. W. J. Am. Chem. Soc. 1993, 115, 5991-6000. (e) Wilson, L. M. Macromolecules 1994, 27, 6683-6686. (f) Pourcain, C. B. St.; Griffin, A. C. Macromolecules 1995, 28, 4116-4121. (g) Lehn, J.-M. Supramolecular Chemistry; VCH: Weinheim, 1995; pp 139-197. (2) (a) Sijbesma, R. P.; Beijer, F. H.; Brunsveld, L.; Folmer, B. J. B.; Hirshberg, J. H. K. K.; Lange, R. F. M.; Lowe, J. K. L.; Meijer, E. W. Science 1997, 278, 1601-1604. (b) Sijbesma, R. P.; Meijer, E. W. Chem. Commun. 2003, 5-168. (c) Ojelund, K.; Loontjens, T.; Steeman, P.; Palmans, A.; Maurer, F. Macromol. Chem. Phys. 2003, 204, 5260.
10.1021/jo050187i CCC: $30.25 © 2005 American Chemical Society
Published on Web 03/19/2005
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Huang et al. TABLE 1. Association Constantsa and Thermodynamic Parametersb for Complexes of Paraquat Derivatives (2a and 2b) with Crown Ethers (1c and 1d) and a Cryptand (3a) complex
Ka × 10-2 (M-1)
∆G294Kc (kJ/mol)
∆Had (kJ/mol)
∆Sad (J/mol‚deg)
3a‚2a 3a‚2b 1c‚2b 1d‚2b
6.0 × 102 6.0 × 102 2.7 ( 0.5 3.5 ( 0.5
-25 -25 -14 -14
-48 -54 -48 -56
-78 -97 -117 -144
than for the cryptand. As expected, the cryptand 3a undergoes significantly less structural change in the analogous process, and this is the major factor in its enhanced binding strength.
a Measured at 21 °C; average of five solutions with the constant host concentration and varying guest concentrations ([guest]0/ [host]0 ) 1-50). Ka values of complexes of 3a were determined previously,5a and the same method was used for complexes of 2b using the time-averaged signals for H2 of 1c and 1d. b Determined by variable-temperature 1H NMR spectroscopy in acetone-d6 and van’t Hoff plots using the time-averaged signals for H1 of 3a and H2 of 1c and 1d. c Estimated error:(5% relative. d Measured from 21 to 50°C; estimated errors: 2σ(I)], max residual density 0.498 e‚Å-3, max/min transmission 0.9647/0.8397, and goodness of fit (F2) ) 1.113. X-ray Analysis of 3b. Colorless crystals of 3b were grown by slow evaporation of a 9:1 chloroform/acetone solution of 3b. X-ray diffraction data were collected on a Siemens Bruker P4 diffractometer by the ω scan method in a range 2.0° e q e 25.0°. SADABS absorption corrections were applied. The structure was solved by direct methods and refined by fullmatrix least squares procedure on F2 using SHELXTL.18 Nonhydrogen atoms were refined with anisotropic displacement coefficients, and hydrogen atoms were treated as idealized contributions. Crystal data: block, colorless, 0.60 × 0.40 × 0.30 mm3, C37H45NO14, FW 727.74, monoclinic, space group C2/c, a ) 17.688(3) Å, b ) 11.184(2) Å, c ) 18.034(5) Å, β ) 96.030(14)°, V ) 3547.9(18) Å3, Z ) 4, Dc ) 1.362 g cm-3, T ) 241K, m ) 1. 05 cm-1, 3555 measured reflections, 2931 independent reflections [R(int) ) 0.0464], 236 parameters, F(000) ) 1544, R1 ) 0.1490, wR2 ) 0.2873 (all data), R1 ) 0.0867, wR2 ) 0.2060 [I > 2s(I)], maximum residual density 0.436 e‚Å-3, and goodness-of-fit (F2) ) 1.573. X-ray Analysis of 3b‚2a. Bright yellow crystals of 3b‚2a were grown by vapor diffusion of pentane into an acetone solution of 3b and 2a (1:1). X-ray diffraction data were collected on an Oxford Diffraction XCalibur2 diffractometer equipped with the Enhance X-ray Source (Mo KR radiation; λ ) 0.71073 Å) and a Sapphire 2 CCD detector by the φ and ω scan method in a range 1.06° e θ e 27.50°. The structure was solved by the direct methods using SIR19 and refined by fullmatrix least squares using Crystals.20 Crystal data: prism, yellow, 0.38 × 0.20 × 0.12 mm3, C58H77F12N3O17P2, FW
2a,
(17) Sheldrick, G. M. SADABS (2.01), Bruker/Siemens Area Detector Absorption Correction Program, Bruker AXS, Madison, WI, 1998. (18) Sheldrick, G. M. SHELXTL NT ver. 6.12; Bruker Analytical X-ray Systems, Inc.: Madison, WI, 2001. (19) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A. J. Appl. Crystallogr. 1993, 26, 343-350. (20) Watkin, D. J.; Prout, C. K.; Carruthers, J. R.; Betteridge, P. W.; Cooper, R. I. CRYSTALS 2000, Issue 11. Chemical Crystallography Laboratory, University of Oxford, Oxford.
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1378.18, monoclinic, space group P21/c, a ) 13.9159(17) Å, b ) 21.217(2) Å, c ) 21.768(2) Å, β ) 95.423(9)°, V ) 6398.3(12) Å3, Z ) 4, Dc ) 1.431 g cm-3, T ) 100 K, m ) 1.73 cm-1, 82374 measured reflections, 20876 independent reflections [R(int) ) 0.03], 829 parameters, F(000) ) 2880.000, R1 ) 0.1950, wR2 ) 0.1524 (all data), R1 ) 0.0618, wR2 ) 0.1223 [I > 2s(I)], maximum residual density 1.32 e‚Å-3, and goodness-of-fit (F2) ) 0.9244. X-ray analysis of 3c•2a•3c. Yellow crystals of 3c‚2a‚3c were grown by vapor diffusion of pentane into a 1:1 acetonitrile:acetone solution of 3c and 2a (1:2 molar ratio). X-ray diffraction data were collected on a Bruker Apex CCD diffractometer equipped with Mo KR radiation (λ ) 0.71073 Å) and a graphite monochromator by the phi and omega scan method in a range 1.06° e θ e 28.28°. SADABS absorption corrections were applied. The structure was solved by direct methods and refined by full-matrix least squares procedure on F2 using SHELXTL.18 Non-hydrogen atoms were refined with anisotropic displacement coefficients, and hydrogen atoms were treated as idealized contributions. Besides the main 3c‚2a‚3c molecule in the crystal structure there are two acetonitrile, water and acetone solvent molecules. The acetone molecule is disordered around a center of symmetry and was treated by SQUEEZE.21 Correction of the X-ray data by SQUEEZE (38 e/cell) was close to the required values (32 e/cell). Crystal data: block, yellow, 0.45 × 0.30 × 0.20 mm3, C46.50H63F6N4O13.50P, FW 1038.98, triclinic, space group P-1, a ) 10.3991(6) Å, b ) 13.6159(8) Å, c ) 19.3423(12) Å, R ) 87.7590(10)°, β ) 82.5240(10)°, γ ) 72.6750(10)°, V ) 2592.3(3) Å3, Z ) 2, Dc ) 1.331 g cm-3, T ) 100K, µ ) 1.40 cm-1, 19230 measured reflections, 11808 independent reflections [R(int) ) 0.0229], 622 parameters, F(000) ) 1094, R1 ) 0.0954, wR2 ) 0.2265 (all data), R1 ) 0.0710, wR2 ) 0.2084 [I > 2σ(I)], maximum residual density 0.816 e ÅÅ-3, and goodness-of-fit (F2) ) 1.067. X-ray Analysis of 3d•2a. Bright yellow crystals of 3d‚2a were grown by vapor diffusion of pentane into an acetone solution of 3d and 2a (1:1). X-ray diffraction data were collected in a range 2.5° e θ e 25.0° on a Nonius KappaCCD diffractometer equipped with Mo KR radiation (λ ) 0.71073 Å), a graphite monochromator, and an Oxford Cryostream chiller. The structure was solved by the direct method SIR19 and refined by full-matrix least-squares using Crystals.20 Nonhydrogen atoms were treated anisotropically and hydrogen atoms were placed in calculated positions. 9851 reflections were used in refinements by full-matrix least-squares on F2. Crystal data: prism, yellow, 0.25 × 0.20 × 0.12 mm3, C52H68F12N2O14P2, FW 1235.04, monoclinic, space group P21/ c, a ) 11.871(3) Å, b ) 23.066(5) Å, c ) 20.450(6) Å, β ) 90.307(8)°, V ) 5599.5(25) Å3, Z ) 4, Dc ) 1.465 g cm-3, T ) 100 K, µ ) 1.84 cm-1, 68453 measured reflections, 9851 independent reflections, 739 parameters, F(000) ) 2576, R1 ) 0.1427, wR2 ) 0.1674 (all data), R1 ) 0.0588, wR2 ) 0.0891 [I > 4σ(I)], max. residual density 0.96 e‚Å-3, max/min transmission 0.979/ 0.940, and goodness-of-fit (F2) ) 1.1035. X-ray Analysis of 3e. Colorless crystals of 3e were grown by slow evaporation of an acetone solution of 3e at room temperature. The chosen crystal was mounted on a nylon CryoLoop (Hampton Research) with Krytox Oil (DuPont) and centered on the goniometer of a Oxford Diffraction XCalibur2 diffractometer equipped with a Sapphire 2 CCD detector. The data collection routine, unit cell refinement, and data processing were carried out with the program CrysAlis.22 The structure was solved by direct methods and refined using the SHELXTL program package.18 The asymmetric unit of the structure comprises two crystallographically independent molecules of 3e, three acetone molecules, and 2.93 water molecules. Successful refinement of the structure was plagued by disorder in one arm of a 3e molecule, the acetone molecules, (21) Van der Sluis, P.; Spek, A. L. Acta Crystallogr., Sect. A 1990, A46, 194-201 (22) CrysAlis v1.170, Oxford Diffraction: Wroclaw, Poland, 2002.
Bis(m-phenylene)-32-crown-10-Based Cryptands and additional residual electron density that was modeled as water. The arm of the 3e molecule was modeled as adopting two conformations that refined to occupancies of 0.528(3) and 0.472(3). The disordered acetone was modeled as adopting two conformations with occupancies of 0.578(7) and 0.422(7). Four strong residual electron density peaks, all within 2.7-3.0 Å of other oxygen atoms were presumed to be the oxygen atoms of water molecules. Two of these Fourier peaks were refined as fully occupied oxygen sites. The remaining two Fourier peaks could not have full occupancy due to their close proximity to the disordered 3e arm, and refined to occupancies 0.432(9) and 0.50(1). The size of the anisotropic thermal parameters in the remaining two acetone molecules as well as the prevalence of residual electron density peaks near the molecules suggest additional disorder which was not modeled successfully. The final refinement involved an anisotropic model for all non-hydrogen atoms and a riding model for all hydrogen atoms. A total of six hydrogen atoms from the disordered 3e molecule, three from the disordered acetone and the hydrogen atoms of the water molecules were all absent from the model. Crystal data: plate, colorless, 0.48 × 0.24 × 0.085 mm3, 2C36H46O12‚3C3H6O‚2.93H2O, FW 1568.48, triclinic, space group P-1, a ) 10.7938(13) Å, b ) 20.2260(19) Å, c ) 21.431(2) Å; R ) 63.096(9)°, β ) 83.239(10)°, γ ) 84.292(9)°; V ) 4137.6(7) Å3, Z ) 2, Dc ) 1.259 g cm-3, T ) 100 K, µ ) 0.96 cm-1, 22982 measured reflections, 14609 independent reflections[R(int) ) 0.0234], 1100 parameters, F(000) ) 1683, R1 ) 0.0889, wR2 ) 0.2076 (all data), R1 ) 0.0699, wR2 ) 0.1926 [I > 2σ(I)], and GooF (F2) ) 1.109. Calculations of Electrostatic Potential Maps of 2a, 3b, 3c, 3d, and 3e at AM1 Level with the CAChe Program.
CAChe WorkSystem Pro Version 6.1 was used in the calculations of electrostatic potential maps of 2a, 3b, 3c, 3d, and 3e. The structures of these compounds were input from their individual crystal structures (2a, 3b, and 3e) or paraquat complex crystal structures (3c‚2a‚3c and 3d‚2a). Then their electrostatic potential maps at AM1 level were calculated under AM1 geometry using the AM1 wave function.
Acknowledgment. This research was supported by the National Science Foundation (DMR0097126) and the American Chemical Society Petroleum Research Fund (40223-AC7). We also thank the NSF (Grant No. CHE-0131128) for funding of the purchase of the Oxford Diffraction Xcalibur2 single-crystal diffractometer. We thank Professor Richard D. Gandour at Virginia Tech for helpful discussions on the calculations of electrostatic potential maps of cryptands and paraquat with the CAChe program. Supporting Information Available: The preliminary crystal structure of 3e‚2a and an X-ray crystallographic file for 2a, 3b, 3b‚2a, 3c‚2a‚3c, 3d‚2a, and 3e, other electrospray ionization mass spectra of cryptand/paraquat complexes, ORTEP diagrams of the X-ray crystal structures of 2a, 3b, and 3e, and proton NMR spectra of cryptands 3b-e. This material is available free of charge via the Internet at http://pubs.acs.org. JO050187I
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