Oligomerization equilibria and dynamics of 2,2-di-n-butyl-1,3,2-dioxastannolanes

Article abstract of DOI:10.1021/ja00160a012

The ¹¹⁹Sn and ¹³C NMR spectra of solutions of 2,2-di-n-butyl-1,3,2-dioxastannolane (1) and a number of its symmetrical derivatives in nonpolar solvents have been studied as functions of temperature and concentration. The compounds studied included (1S,6S)-8,8-di-n-butyl-7,9,8-dioxastannabicyclo[4.3.0]nonane (2), obtained from di-n-butyltin oxide and (S,S)-1,2-cyclohexanediol. A new method of resolution of trans-1,2-cyclohexanediol has been developed. Solutions of 1, 2, and related derivatives of disecondary diols were found to contain mixtures of oligomers that have been identified as dimers, trimers, tetramers, and pentamers. In contrast to earlier work, no evidence for the presence of monomers was obtained. The compositions of the mixtures are extremely temperature dependent; trimers and tetramers are the major constituents below -20 °C, but dimers increasingly dominate as the temperature is raised. Thermodynamic parameters for the equilibria of 1 and 2 have been measured. A derivative of a ditertiary diol, 2,2-di-n-butyl-4,4,5,5-tetramethyl-1,3.2-dioxastannolane, exists in nonpolar solvents predominantly as a dimer over the temperature range studied, from -60 to +80 °C. Activation parameters for a process in this dimer that causes the ¹³C NMR signals of the pairs of nonequivalent methyl carbons to coalesce have been determined by total line shape analysis. A series of related reversible associative processes involving dimers, trimers, tetramers, pentamers, and possibly monomers and hexamers accounts for the changes observed in the NMR spectra with temperature.