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

The binary ⁿBu₂SnCl]₂O/ⁿBu₂SnOAc]₂O (OAc=O₂CCH₃) system is re-examined using ¹¹⁹Sn-NMR spectroscopy. Binary mixtures of ⁿBu₂SnCl]₂O and ⁿBu₂SnOAc]₂O 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 ¹¹⁹Sn-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 ¹¹⁹Sn spectral data of the binary system leads to the unambiguous assignment of the tin resonances of {ⁿBu₂SnOAc]₂O}₂: δ_exo=−216.1 ppm, δ_endo=−227.9 ppm.