Reaction of trialkylstannyllithium and hexaalkydistanne. 1H and 119Sn NMR studies

Abstract

The reaction of hexamethyldiatannane (Me 3SnSnMe 3) with metallic lithium in tetrahydrofuran (THF) has been studied by 1H and 119Sn NMR spectroscopy. All spectra displayed a single peak which moved gradually from the chemical shift Of Me 3SnSnMe 3 (0.22 ppm in 1H NMR and −108.7 ppm in 119 Sn NMR) into those of trimethylstannyllithium (Me 3SnLi, −0.37 ppm, −182.7 ppm) in 2 h. A mixture of Me 3SnSnMe 3 and Me 3SnLi in THF also showed only a single peak both in the 1H and 119Sn NMR spectra. There was a linear relationship between the chemical shift of the singlet and the amount of lithium per trimethylstannyl group (Li/Me 3Sn). The equilibration of the Me 3Sn group between the two species was proposed as a plausible explanation for the apparent equivalency of M 3 and was supported by investigating two mixed alkyl systems. Both the Me 3SnLi-F 1t 3SnSnEt 3 and Et 3SnSnMe 3SnSnMe 3 systems showed single Me 3Sn and Et 3Sn group resonances each in the NMR spectra. The chemical shift of Me 3Sn vs (Li/R 3Sn) in 119Sn NMR spectra, however, deviated considerably to higher field from the linear relationship, while that of Et 3Sn shifted to lower field. This can be interpreted in terms of the rapid exchange between Me 3Sn and Et 3Sn in the following two equilibria. ▪ ▪