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Correlating Solution- and Solid-State Structures of Conformationally Flexible Resorcinarenes: Significance of a Sulfonyl Group in Intramolecular Self-Inclusion
Authors:Małgorzata Pamuła  Prof Maija Nissinen  Dr Kaisa Helttunen
Institution:Department of Chemistry, Nanoscience Center, University of Jyvaskyla, P.O. Box 35, 40014 Jyvaskyla, Finland
Abstract:The synthesis of tetramethoxyresorcinarene podands bearing p-toluene arms connected by -SO3- ( 1 ) and -CH2O- ( 2 ) linkers is presented herein. In the solid state, the resorcinarene podand 1 forms an intramolecular self-inclusion complex with the pendant p-toluene group of a podand arm, whereas the resorcinarene podand 2 does not show self-inclusion. The conformations of the flexible resorcinarene podands in solution were investigated by variable-temperature experiments using 1D and 2D NMR spectroscopic techniques as well as by computational methods, including a conformational search and subsequent DFT optimisation of representative structures. The 1H NMR spectra of 1 and 2 at room temperature show a single set of proton signals that are in agreement with C4v symmetry. At low temperatures, the molecules exist as a mixture of boat conformations featuring slow exchange on the NMR timescale. Energy barriers (ΔG298) of 55.5 and 52.0 kJ mol−1 were calculated for the boat-to-boat exchange of 1 and 2 , respectively. The results of the ROESY experiments performed at 193 K and computational modelling suggest that in solution the resorcinarene podand 1 adopts a similar conformation to that present in its crystal structure, whereas podand 2 populates a more versatile range of conformations in solution.
Keywords:inclusion compounds  resorcinarenes  solution structures  supramolecular chemistry  X-ray diffraction
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