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.
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.
Yip
Wing-Ping
WP
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.
Yu
Wing-Yiu
WY
Zhu
Nianyong
N
Che
Chi-Ming
CM
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*
C499747:1,4,7-trimethyl-1,4,7-triazacyclononane; D000475:Alkenes; D001372:Aza Compounds; D009942:Organometallic Compounds; D012428:Ruthenium