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 ""n 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 pprn 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 'I9Sn NMR spectroscopy. The principal components of the 119 Sn 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 pprn 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 '19sn spin-lattice relaxation in these compounds.Key words: 1,3,2-dioxastannolanes, stannylene acetals, 'I9Sn NMR, '"Sn NMR of solids, '"Sn chemical shift anisotropy. Pour les quatre composCs pour lesquels on a determint des structures par diffraction des rayons-X, on a pu relie les nombres et les positions des pics isotropes dans les spectres haute resolution avec le nombre des sites d'Ctain presents et 1'Ctat d'oligomerisation des composCs. Les dCplacements chimiques des noyaux de Sn hexacoordonnCs sont de 35 80 pprn plus grands dans les polymkres solides que dans les m&mes composCs en solution alors que les composes existent sous la forme de trimkres ou de tktramkres. Faisant appel a la RMN du 'I9sn par CP/MAS, on a determink les Ctats d'oligomkrisation des solides que I'on n'avait pas CtudiCs anterieurement par diffraction des rayons-X. En se basant sur les spectres statiques, on a obtenu les principales composantes des tenseurs des deplacements chimiques du 'I9Sn et on les a utilisees pour calculer les anisotropies des dCplacements chimiques et les parametres dlasymCtrie. Pour les 1,3,2-dioxastannolanes, les valeurs des anisotropies des deplacements chimiques varient de 600 a 800 ppm; toutefois, pour un 1,3,2-dioxastannane, cette anisotropie est plus ClevCe, soit 919 ppm. Lorsque le m&me oligomere est present dans les deux Ctats, les anisotropies des deplacements chimiques mesures directement a partir des patrons de poudres a 1'Ctat solide sont en tres bon accord avec les valeurs obtenues ...

Control of regioselectivity in reactions of dialkylstannylene acetals. Part II. NMR results and mechanistic analysis

“…previously that hexacoordinate peaks in tetramers are less shielded than those in trimers (13). The dimer peak and the pentacoordinate tin tetramer peak occurred at the same chemical shift for 2sa in toluene-cl,.…”

“…These chemical shift values are halfway between those of the first type and that of a di-tertalkylstannylene acetal, 2,2-di-tert-butyl-1,3,2-dioxastannolane, -225 pprn (9). This latter compound was shown to exist as a dimer both in the solid state and in solution (9,13). Thus, disec-alkylstannylene acetals also exist in solution as single symmetric dimers to the level of detection by Il9sn NMR spectros-COPY.…”

The structure of 2,2-dibutyl-1,3,2-dioxastannane in the solid state and in solution

“…The average (10,26). Large variations in ' "~n nmr chemical shifts with temperature preclude precise definition of the species present but average values more negative than -280 pprn would be expected for higher oligomers than the pentamer.…”

“…Similar trends have been observed for tetraalkyltin and lead derivatives (1 6d). N~tclear rnagrzetic resonance spectral results for the solid Static and CP/MAS"'S~ nrnr spectra of crystalline 1 were measured (10). An expansion of the region of the CP/MAS spectrum containing the isotropic peaks is shown in Fig.…”

“…A preliminary X-ray diffraction study published in 1973 suggested that solid 1 was a polymer but no details other than the Sn-0 bond lengths were supplied (14). Recently, " 9~n nmr spectra of 1 in the solid state have been measured and the results support the assignment of the structure of 1 as a polymer (10). Molecular weight measurements in pyridine by boiling point elevation gave values of 333 (14) and, for a higher concentration (4.2%), 550 (15).…”