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

Grindley, T. Bruce; Thangarasa, Rasiah

doi:10.1021/ja00160a012

Cited by 38 publications

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“…A single sharp peak in each 'I9Sn NMR spectrum at room temperature suggests that only one of the three possible dimers is being observed. In previous work, Il9Sn NMR spectra of stannylene acetals that contained more than one species at room temperature were either broad or contained more than one line (4,11). The 13c NMR spectra of the type (i) compounds are also consistent with single dimeric species because only single sets of peaks were observed.…”

Section: Resultsmentioning

confidence: 77%

“…Tin-119 NMR chemical shifts are listed in Table 1. The ll9Sn NMR spectra of most dialkylstannylene acetals contained a single sharp peak at room temperature with a chemical shift typical of pentacoordinate tin atoms (4,11). If tin atoms are only present in pentacoordinate environments, the only species present are dimers.…”

Section: Resultsmentioning

confidence: 99%

“…There are known to be large temperature effects on dimeroligomer equilibria (4,11). Even for compounds in which oligomers are dominant at -100°C, dimers constitute the majority of the species present at room temperature.…”

Section: Resultsmentioning

confidence: 99%

“…More highly substituted stannylene acetals are mostly present as dimers in the solid state (7)(8)(9), although one has been found to be a pentamer (10). In solution, compounds 11 and 12 exist as highly temperature dependent mixtures of dimers and oligomers that shift towards the less aggregated species as the temperature is raised (6,11). More substituted compounds, such as carbohydrate-derived stannylene acetals, have been found to be present in solution mainly as dimers (4,9).…”

Section: Introductionmentioning

confidence: 99%

“…Tin-1 19 NMR spectroscopy is the best method available to study the composition of solutions of dibutylstannylene acetals (4,6,11). The region of the NMR spectrum where absorption occurs is related to the coordination status of the tin atoms; tetracoordinate tin atoms in dialkoxydialkyltin compounds absorb at chemical shifts greater than -40 ppm, pentacoordinate tin atoms absorb between -80 and -190 ppm, and hexacoordinate tin atoms have shifts less than -200 ppm.…”

Section: Introductionmentioning

confidence: 99%

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

Kong¹,

Grindley²

1994

Can. J. Chem.

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The ""n NMR spectra of dialkylstannylene acetals derived from a number of carbohydrate-based terminal 1,2-diols have been recorded. The spectra of chloroform-d solutions at room temperature of most of these dialkylstannylene acetals were consistent with the presence of single symmetric dimers only although some did contain small proportions of higher oligomers. A general mechanistic scheme is presented that explains the regioselectivity of p-toluenesulfonation reactions of dialkylstannylene acetals presented in the preceding paper. In the scheme, the reaction intermediates are the dialkylstannylene acetal dimers. Forptoluenesulfonation reactions, equilibration between the three possible dimers is faster than reaction with p-toluenesulfonyl chloride. Reaction regioselectivity depends both on the position of the dimer equilibrium and on the rates of reaction of individual dicoordinate oxygen atoms in the dimers. ' The general scheme was also used to explain the regioselectivity obtained for the very fast oxidation reactions of dialkylstannylene acetals with bromine or N-bromosuccinimide. In these kinetically controlled reactions, regiochemistry is determined by the initial reaction of dicoordinate oxygen atoms in the most populated dimer(s) with the electrophilic oxidizing reagent.XIANQI KONG et T. BRUCE GRINDLEY. Can. J. Chem. 72,2405Chem. 72, (1994. On a determine les spectres RMN du '19sn d'acttals de dialkylstannylknes obtenus h partir d'un certain nombre de 1,2-diols dtrivCs d'hydrates de carbone. Les spectres de la plupart de ces acttals de dialkylstannylkne, obtenus h la temperature ambiante, pour des solutions dans le chloroforme-d, sont en accord avec la prtsence de dimkres symttriques uniques, m&me si certains contiennent de faibles proportions d'oligomkres de masses plus tlevtes. On propose un schtma mkcanistique gCntral pour expliquer la rtgiostlectivite des rtactions de p-toluknesulfonation des acttals de dialkylstannylknes prtsenttes dans la communication prectdente. Dans ce schtma, les intermtdiaires rtactionnels sont les acttals de dialkylstannylknes dimkres. Pour les reactions de p-toluknesulfonation, I'tquilibre entre les trois dimkres possibles est plus rapide que la rtaction avec le chlorure de p-toluenesulfonyle. La rCgiosClectivite de la rtaction dtpend ? I la fois de la position de I'tquilibre du dimkre et des vitesses de rtaction des atomes d'oxygkne dicoordints individuels dans les dimkres. On a aussi utilist le schtma gtntral pour expliquer la rCgiosClectivitt observte lors de rkactions d'oxydation trks rapides des acttals de dialkylstannylknes par le brome ou par la N-bromosuccinimide. Dans ces reactions sous contrale cinttique, la rtgiochimie est dtterminte par la rtaction initiale des atomes d'oxygkne dicoordinCs dans le(s) dimkre(s) le(s) plus populeux avec le rtactif oxydant tlectrophile.[Traduit par la redaction]

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Section: Resultsmentioning

confidence: 77%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%