Tin-119 NMR of 1,3,2-dioxastannolanes and a 1,3,2-dioxastannane in the solid state

Abstract

The cross-polarized static and high-resolution magic angle spinning 119Sn NMR spectra of a number of 2,2-dialkyl-1,3,2-dioxastannolanes and one 1,3,2-dioxastannane have been measured in the solid state. For the four compounds on which X-ray studies had been performed, the numbers and positions of the isotropic peaks in the high-resolution spectra were related to the number of tin sites present and the state of oligomerization of the compounds. The chemical shifts of hexacoordinate Sn nuclei are 35–80 ppm larger in polymeric solids than for the same compounds in solution where the compounds exist as trimers and tetramers. States of oligomerization for solids that had not been previously studied by X-ray crystallography were determined using CP/MAS 119Sn NMR spectroscopy. The principal components of the 119Sn chemical shift tensors were obtained from the static spectra and used to calculate chemical shift anisotropies and asymmetry parameters. The values of the chemical shift anisotropies ranged from 600 to 800 ppm for 1,3,2-dioxastannolanes but the value for a 1,3,2-dioxastannane was larger, 919 ppm. The chemical shift anisotropies measured directly from the solid-state powder patterns are in excellent agreement with the values derived from previous variable temperature spin-lattice relaxation measurements in solution when the same oligomer was present in both states. Our results support our previous conclusion that the antisymmetric terms of the chemical shift tensor make a small or negligible contribution to the rate of 119Sn spin-lattice relaxation in these compounds. Keywords: 1,3,2-dioxastannolanes, stannylene acetals, 119Sn NMR, 119Sn NMR of solids, 119Sn chemical shift an-isotropy.