Macrocycles Containing Tin. The Preparation of Macrobicyclic Lewis Acidic Hosts Containing Two Tin Atoms and 119-Sn NMR (Nuclear Magnetic Resonance) Studies of Their Chloride and Bromide Binding Properties in Solution

摘要

The preparation of eight symmetrical, macrobicyclic hosts containing two chloride or bromide substituted tin atoms at the bridgehead positions and linking chains of 6, 7, 8, 10, 12 methylene groups are described. In solution, the smaller members exist as one isomer with the halogens outside of the cavity (out-out isomer), but the larger members exist as a mixture of the major out-out isomer and a minor in-out isomer that contains one halogen inside the cavity. Complexation of chloride anion by the five chloride substituted hosts and of bromide anion by the three bromide substituted hosts in halogenated solvents was studied by (119) Sn NMR spectroscopy. All of the bicyclic hosts that bind halide form complexes with 1:1 stoichiometry with a guest anion encrypted within the cavity of the host. Equilibrium constants for formation of the complexes were measured. Temperature dependent dynamic NMR behavior was observed for four bicyclic hosts binding chloride and for one host binding bromide, and simulations of the spectra measured at various temperatures provided rate constants for binding guest anion within the cavity and for dissociation of the guest anion from cavity. Arrhenius functions for these processes were calculated. Size selective binding was observed in both chloride and bromide binding. For chloride complexation, the rate of formation of complexes at 20 deg C increased monotonically as a function of the linking chain length, but the rate of dissociation did not.