Tin-119 NMR studies on some adducts of tin(IV) halides

Abstract

Tin-119 and phosphorus-31 NMR spectra have been recorded for SnCI 4L 2, SnBr 4L 2 (L = tributylphosphine oxide) and mixtures thereof. The compound SnCl 4L 2 exists predominantly as the trans L 2 isomer with a small proportion of the cis L 2 isomer also present in solution whereas SnBr 4L 2 appears to be present only as the trans L 2 isomer. In the mixed solution all the trans snCI xBr 4−xL 2 species are observed. The anionic complexes [SnCI 5- L] − and [SnBr 5L] − both show slight dissociation in solution to SnX 4L 2 and [SnX 6] 2− (X = CI, Br). The tin-199 NMR spectrum of an equimolar mixture of [SnCI 5L] − and [SnBr 5L] − shows ten of the possible twelve [SnCI xBr 5-xL] − species. In contrast, SnX 4L 2 (L′ = acetone; X = CI, Br) exist predominantly as cis L′ 2 isomers. A 1:1 mixture of the complexes in dichloromethane solution at −50 °C shows average tin-119 resonances for each stoichiometry of mixed halo species cis SnCI xBr 4-xL′ 2. Subsequent cooling to −100 °C slows intramolecular processes sufficiently to enable observation and identification of most of the individual geometric isomers of each stoichiometry. The anionic complexes [SnCI 5L′ − and [SnBr 5L′ − show no appreciable dissociation in dichloromethane solution and the tin-119 spectrum of a 1:1 mixture of these compounds at −100 °C shows only six resonances corresponding to various [SnCI xBr 5-xL′] − species without distinguishing between individual isomers of each stoichiometry. Cooling to −100 °C enables identification of some of these isomers. The pairwise additivity model, using previously established interaction parameters, was used to assign all isomers species observed in the tin-119 spectra of these systems.