New proton-ionizable lariat ethers with picrylamino-type side arms and their alkali metal salts. Synthesis and structural studies

Twelve novel proton-ionizable dibenzo lariat ethers with picrylamino-type sidearms attached to the central carbon of a three-carbon bridge have been prepared in high yields by a three-step synthesis from the lariat ether alcohols via the corresponding lariat ether mesylates and amines. Structural studies conducted in solution by H-1 NMR spectroscopy and in the solid state by X-ray diffraction show that the picrylamino-type lariat ethers are preorganized for metal ion complexation with the sidearms oriented toward the macrocyclic polyether cavities due to intramolecular NH ... O bonding. Structural investigations of the alkali metal salts of representative ionized picrylamino-lariat ethers in solution demonstrate cooperative coordination of the metal cation by the macrocyclic polyether unit and the ionized sidearm that serves as the counterion with the negative charge localized on the one of o-nitro groups. In the Li+ salt of ionized sym-(picrylamino)-dibenzo-14-crown-4, this places the aromatic ring of the sidearm perpendicular to the plane of the four ring oxygens.