Hydrogen bond based noncovalent association in the semi-fluorous solvent perfluorobutyl-methyl ether: Host-host and host-guest association of the host 1-(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-Heptadecafluoro-decyl)-3-pyridin-2-yl-urea

Abstract

A fluorous pyridyl-urea, 1-(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluoro-decyl)-3-pyridin-2-yl-urea, was prepared to act as a host and analyzed by 1H NMR inCD2Cl2 and perfluorobutyl-methyl ether (HFE7100). Crystals were analyzed by X-ray diffraction. The host molecules were found to form pillar-like structures in the crystal. There is an intramolecular bond between the pyridyl nitrogen and one urea hydrogen. 1H NMR spectra demonstrated that the urea hydrogens’ positions shift as the concentration of the host changes. The dependence of the shifts on concentration are consistent with the formation of a trimer of hosts with a logKeq for formation of trimer from monomer approximately 6. Association of the host with guests octanoic acid, ethyl acetate, N-ethylacetamide, N,N-dimethylacetamide, and acetone, was analyzed by titration of the host with individual guests in HFE7100 solvent. Downfield or upfield shifts of the urea hydrogens were used to indicate hydrogen bond formation with the guest. Acetone and ethyl acetate were unable to overcome the self-association of the host and form host-guest complexes. Octanoic acid binding caused shifts in the 1H NMR spectra of one hydrogen of the urea group. N-ethylacetamide and N,N-dimethylacetamide induced shifts in both urea hydrogens. The results indicate that the host monomer’s favored conformation contains an intramolecular hydrogen bond. This bond is not broken upon association with octanoic acid, but it is broken upon association with the two acetamides