Stereoisomerization of Hexacoordinate Sulfur and Tellurium

The reaction of bromine trifluoride with sulfurane 1 gives rise to the first reported isolation of geometrical isomers of 12-S-6 sulfur, the trans- and cis-persulfuranes 2 and 3. The cis isomer is 2.0 (+OR-) 0.1 kcal/mol more favored in free energy than the all trans isomer in methylene chloride solution at 25(DEGREES)C. Calorimetry showed the trans-to-cis isomerization to be exothermic by 1.6 (+OR-) 0.5 kcal/mol. The rapid, acid-catalyzed isomerization of trans isomer 2 to give cis isomer 3 occurs by a dissociative mechanism through a pentacoordinate cationic sulfur intermediate, a 10-S-5 persulfonium ion, which was isolated as its hexafluorophosphate salt. A lower limit for the activation barrier of the unobserved nondissociative isomerization of 2 to 3 is 50 kcal/mol in quinoline solution. Polarization and other effects on the relative bond lengths and energies of the isomers are discussed. The results of complete X-ray structure determinations for 2 and 3 are described together with a PMO argument rationalizing the observed order of bond lengths.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Michalak, Ronald Stanley

• Chemistry, Organic

Identifier

(UMI)AAI8302936

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/70201