The Syntheses and Structural Characterizations of Some Monoaza- and Diaza-crown Ethers

Several aza-crown ethers have been synthesized and their structures determined by X-ray crystallography. In a modified synthesis of diaza-18-crown-6 we isolated two of the intermediates, viz. the NaI salt (1) of N,N′-dibenzyldiaza- 18-crown-6 and the salt-free macrocycle (2), and determined their stuctures. In compound (1) a hydrated crown-encapsulated sodium cation was revealed with both benzyl groups folded down and away from the water molecule while in compound (2) a centrosymmetric crown with the benzyl groups splayed out from the ring was found. In addition, we have determined the X-ray crystal structures of monoaza-18-crown-6 and the hydrochloride salt of monoaza-15-crown-5. In the former, the crown resides on an inversion centre showing N/O disorder, and in the latter the protonated amine hydrogen bonds with the chloride anion.