Lariat ethers with fluoroaryl side-arms: a study of CF?metal cation interaction in the complexes of N-(o-fluoroaryl)azacrown ethers?

Dalton Transactions Pub Date: 2008-12-04 DOI: 10.1039/B807199C

Abstract

New lariat ethers, N-(o-fluorophenyl)aza-15-crown-5 (F-A15C5) and N,N′-bis(o-fluorophenyl)diaza-18-crown-6 (F2-A218C6), were prepared by the N-arylation of the corresponding azacrown ethers. The interaction of the ligands with metal cations was studied in solution by 1H and 19F NMR (in acetone-d6) and UV spectroscopy (MeOH) confirming the formation of complexes of F2-A218C6 with K+, Na+, Ag+, Ba2+, Pb2+ and of F-A15C5 with Na+ and giving evidence of CF?metal cation interaction. Cation binding constants (β, evaluated by UV titration method), demonstrate that F-A15C5 and F2-A218C6 form more stable complexes than their fluorine-free analogs. The effect depends on the nature of the metal cation and is at a maximum for hard, singly charged cations (up to 3 logβ units for K+ complex of F2-A218C6). The X-ray structures of complexes [Pb(F2-A218C6)(H2O)](ClO4)2 (1) and [Ba(F2-A218C6)(ClO4)2] (2) reveal short Pb–F (2.805 ?) and Ba–F (2.965 ?) contacts. Complex 2 is centrosymmetric (Ci), while complex 1 has C2 symmetry with one-side coordination of o-fluorophenyl groups to Pb2+. This “one-side” coordination mode of Pb2+ is indicative of a partial localization of the Pb2+ lone pair.

Graphical abstract: Lariat ethers with fluoroaryl side-arms: a study of CF?metal cation interaction in the complexes of N-(o-fluoroaryl)azacrown ethers
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