Macrocycles Containing Tin. 119Sn NMR Studies of Chloride Binding by Lewis Acidic Tin Compounds. Update

摘要

This report updates and corrects information in Technical Report No. 6 (September 15, 1985). New data includes concentration effects on tin-119 chemical shifts, measurements of chemical shifts of dibutyltin dichloride (5) plus chloride ion at low concentrations, direct determination of relative complexing strengths of acyclic model 5 against macrocyclic hosts and modified calculations of host-guest binding energies in acetonitrile. Three macrocyclic Lewis acidic hosts containing two symmetrically disposed dichlorostanna moieties (1-3, ring sizes 18, 22, 26 atoms, respectively) have been prepared as has an acyclic di-tin model, 5,5-16,16-tetrachloro-5,16-distannadocosane (4). The complexation of 1-4 and dibutyltin dichloride (5) with chloride ion in acetonitrile was studied by tin-119 NMR spectroscopy. Rapid exchange of chloride between tin atoms occurred at all ratios of chloride to host studied. An iterative computer program was used to provide estimates of the binding constants of 1, 2, 4 and 5 with chloride. Competition experiments were performed wherein two hosts competed for limited chloride ion, and the tin-119 NMR spectra of the mixtures were analyzed to determine the relative amount of chloride bound by each host and hence the ratio of the binding constants for the two hosts. Good agreement between the relative binding constants found in the latter studies and the ratios of the absolute binding constants found in the former studies was found.