119Sn-NMR spectroscopic study of the 1,3-dichloro- and 1,3-diacetoxytetra-n-butyldistannoxane binary system

The binary [(Bu2SnCl)-Bu-n](2)O/[(Bu2SnOAc)-Bu-n](2)O (OAc= O2CCH3) system is re-examined using Sn-119-NMR spectroscopy. Binary mixtures of [(Bu2SnCl)-Bu-n](2)O and [(Bu2SnOAc)-Bu-n](2)O reach equilibrium rapidly, producing all five possible mixed distannoxane dimers, differing in the ratio and relative positions of Cl and acetoxy ligands. The rapid formation of the product dimers results from the intermolecular exchange of the ligands one at a time. The Sn-119-NMR spectral data are consistent with time-averaged ladder structures arising from rapidly interconverting ladder pairs. The equilibrium concentrations of the binary mixtures indicate that positional ordering of the ligands exists in the mixed dimers. A reversible configurational rearrangement is also observed in which the ligands associated with the same exocyclic tin atom undergo mutual exchange via rotation about the oxygen-exocyclic tin bond. The Sn-119 spectral data of the binary system leads to the unambiguous assignment of the tin resonances of {[(Bu2SnOAc)-Bu-n](2)O}(2): delta (exo) = - 216.1 ppm, delta (endo) = - 227.9 ppm (C) 2001 Elsevier Science B.V. All rights reserved.