Kinetic role of t-amines in the ligand inhibited osmium tetraoxide catalyzed trimethylamine-N-oxide dihydroxylation of alkenes

Erdik E., KAHYA N. D.

TRANSITION METAL CHEMISTRY, vol.28, no.6, pp.658-664, 2003 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 28 Issue: 6
  • Publication Date: 2003
  • Doi Number: 10.1023/a:1025435708610
  • Journal Name: TRANSITION METAL CHEMISTRY
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.658-664
  • Ankara University Affiliated: Yes

Abstract

Kinetic studies on the t-amine inhibited catalytic OsO4 dihydroxylation of cyclooctene, octene, styrene and 4-methyl-, 4-methoxy-, 4-chloro-, 4-(chloromethyl), 4-(trifluoromethyl) and 3-chloro-derivatives of styrene with Me3NO in t-BuOH have been carried out at 50 degreesC. The reactions follow identical kinetics: first order in total osmium species, first order in Me3NO and zero order in alkene. All t-amines have been found to retard the catalysis and the reaction order in t-amine changes from inverse first order to zero. The involvement of dioxomonoglycolataosmium(VI) esters and their monoamine adducts in the rate-determining oxidation step was established by the linear plots of 1/Deltak(2) versus. 1/[L] where Deltak(2) is the decrease in second order rate constant in the presence of [L] concentration of t-amine ligand. Beyond a definite concentration of t-amine, the rate reaches a minimum and remains constant. Activation parameters were evaluated for catalytic OsO4 dihydroxylation of 4-(chloromethyl)styrene at different t-amine concentrations. The values of DeltaH(.) and DeltaS(.) are consistent with the proposed mechanism.