title: Alkene cis-dihydroxylation by [(Me3tacn)(CF3CO2)RuVI O2)]ClO4(Me(3)tacn = 1,4,7-Trimethyl-1,4,7-triazacyclononane): structural characterization of [3 + 2] cycloadducts and kinetic studies.
abstract: cis-Dioxoruthenium(VI) complex [(Me(3)tacn)(CF(3)CO(2))Ru(VI)O(2)]ClO(4) (1, Me(3)tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane) reacted with alkenes in aqueous tert-butyl alcohol to afford cis-1,2-diols in excellent yields under ambient conditions. When the reactions of 1 with alkenes were conducted in acetonitrile, oxidative C=C cleavage reaction prevailed giving carbonyl products in >90% yields without any cis-diol formation. The alkene cis-dihydroxylation and C=C cleavage reactions proceed via the formation of a [3 + 2] cycloadduct between 1 and alkenes, analogous to the related reactions with alkynes [Che et al. J. Am. Chem. Soc. 2000, 122, 11380]. With cyclooctene and trans-beta-methylstyrene as substrates, the Ru(III) cycloadducts (4a) and (4b) [formula; see text] were isolated and structurally characterized by X-ray crystal analyses. The kinetics of the reactions of 1 with a series of p-substituted styrenes has been studied in acetonitrile by stopped-flow spectrophotometry. The second-order rate constants varied by 14-fold despite an overall span of 1.3 V for the one-electron oxidation potentials of alkenes. Secondary kinetic isotope effect (KIE) was observed for the oxidation of beta-d(2)-styrene (k(H)/k(D) = 0.83 +/- 0.04) and alpha-deuteriostyrene (k(H)/k(D) = 0.96 +/- 0.03), which, together with the stereoselectivity of cis-alkene oxidation by 1, is in favor of a concerted mechanism.
authors.affiliation: Department of Chemistry and Open Laboratory of Chemical Biology, Institute of Molecular Technology for Drug Discovery and Synthesis, The University of Hong Kong, Pokfulam Road, Hong Kong.
authors.forename: Wing-Ping
authors.initials: WP
authors.lastname: Yip
authors.forename: Wing-Yiu
authors.initials: WY
authors.lastname: Yu
authors.forename: Nianyong
authors.initials: N
authors.lastname: Zhu
authors.forename: Chi-Ming
authors.initials: CM
authors.lastname: Che
mesh_terms: D000475:Alkenes / Q000138:chemical synthesis* / Q000737:chemistry*; D001372:Aza Compounds / Q000737:chemistry*; D018360:Crystallography, X-Ray; D003500:Cyclization; D006900:Hydroxylation; D007700:Kinetics; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D012428:Ruthenium / Q000737:chemistry*
chemical_list: C499747:1,4,7-trimethyl-1,4,7-triazacyclononane; D000475:Alkenes; D001372:Aza Compounds; D009942:Organometallic Compounds; D012428:Ruthenium