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Article: Kinetics of C-H bond and alkene oxidation by trans-dioxoruthenium(VI) porphyrins

TitleKinetics of C-H bond and alkene oxidation by trans-dioxoruthenium(VI) porphyrins
Authors
Issue Date1991
PublisherRoyal Society of Chemistry. The Journal's web site is located at http://www.rsc.org/dalton
Citation
Journal Of The Chemical Society, Dalton Transactions, 1991 n. 11, p. 2933-2939 How to Cite?
AbstractA series of [RuVILO2] complexes (H2L = Para-substituted tetraphenylporphyrins) have been synthesised and characterized, and the kinetics and mechanism of oxidation of the C-H bond and alkenes investigated. The complexes were selective towards tertiary C-H bonds in saturated alkanes but were almost inactive towards secondary C-H bonds. However, they were reactive towards aromatic hydrocarbons and the second-order rate constants (k2) for the oxidation of ethylbenzene and cumene by [Ru(tpp)O2] (tpp = 5, 10, 15, 20-tetraphenylporphyrinate) were 2.21 × 10-4 and 3.16 × 10-4dm3 mol-1 s-1 respectively. A kinetic isotope effect (KH/KD) of 11.7 was found for the allylic oxidation of cyclohexene by [Ru(tpp)O2]. The major organic products of the oxidation of alkenes in CH2Cl2-MeOH mixtures were epoxides and [Ru(tpp)O2] gave a monomeric product formulated as [RuIV(tpp)O]·EtOH. or [RuIV(tpp)(OH)2·]EtOH. Similar reactions with [RuVI(oep)O2] (oep = 2,3,7,8,12,13,17,18-octaethylporphyrinate) gave [{RuVI(oep)(OH)}2O] in non-co-ordinating solvents. The observed rate law for alkene oxidation was rate = K2[RuVI][alkene]. There exists an almost linerar free-energy relationship between log k2 and E1/2 (one-electron oxidation potentials of alkenes) with slope = -1.1 V-1 for the [Ru(tpp)O2] system. Activation parameters have been determined for the oxidation of styrene, norbornene and cyclooctene by [RuVILO2]. Non-linear and U-shaped Hammett plots were observed for the oxidation of substituted styrenes. The mechanism of alkene oxidation is proposed to involve a continum of transition states, the structures of which may change and be stabilized by defferent substituents.
Persistent Identifierhttp://hdl.handle.net/10722/167846
ISSN
2002 Impact Factor: 3.023
ISI Accession Number ID

 

DC FieldValueLanguage
dc.contributor.authorHo, Cen_US
dc.contributor.authorLeung, WHen_US
dc.contributor.authorChe, CMen_US
dc.date.accessioned2012-10-08T03:12:10Z-
dc.date.available2012-10-08T03:12:10Z-
dc.date.issued1991en_US
dc.identifier.citationJournal Of The Chemical Society, Dalton Transactions, 1991 n. 11, p. 2933-2939en_US
dc.identifier.issn1472-7773en_US
dc.identifier.urihttp://hdl.handle.net/10722/167846-
dc.description.abstractA series of [RuVILO2] complexes (H2L = Para-substituted tetraphenylporphyrins) have been synthesised and characterized, and the kinetics and mechanism of oxidation of the C-H bond and alkenes investigated. The complexes were selective towards tertiary C-H bonds in saturated alkanes but were almost inactive towards secondary C-H bonds. However, they were reactive towards aromatic hydrocarbons and the second-order rate constants (k2) for the oxidation of ethylbenzene and cumene by [Ru(tpp)O2] (tpp = 5, 10, 15, 20-tetraphenylporphyrinate) were 2.21 × 10-4 and 3.16 × 10-4dm3 mol-1 s-1 respectively. A kinetic isotope effect (KH/KD) of 11.7 was found for the allylic oxidation of cyclohexene by [Ru(tpp)O2]. The major organic products of the oxidation of alkenes in CH2Cl2-MeOH mixtures were epoxides and [Ru(tpp)O2] gave a monomeric product formulated as [RuIV(tpp)O]·EtOH. or [RuIV(tpp)(OH)2·]EtOH. Similar reactions with [RuVI(oep)O2] (oep = 2,3,7,8,12,13,17,18-octaethylporphyrinate) gave [{RuVI(oep)(OH)}2O] in non-co-ordinating solvents. The observed rate law for alkene oxidation was rate = K2[RuVI][alkene]. There exists an almost linerar free-energy relationship between log k2 and E1/2 (one-electron oxidation potentials of alkenes) with slope = -1.1 V-1 for the [Ru(tpp)O2] system. Activation parameters have been determined for the oxidation of styrene, norbornene and cyclooctene by [RuVILO2]. Non-linear and U-shaped Hammett plots were observed for the oxidation of substituted styrenes. The mechanism of alkene oxidation is proposed to involve a continum of transition states, the structures of which may change and be stabilized by defferent substituents.en_US
dc.languageengen_US
dc.publisherRoyal Society of Chemistry. The Journal's web site is located at http://www.rsc.org/daltonen_US
dc.relation.ispartofJournal of the Chemical Society, Dalton Transactionsen_US
dc.titleKinetics of C-H bond and alkene oxidation by trans-dioxoruthenium(VI) porphyrinsen_US
dc.typeArticleen_US
dc.identifier.emailChe, CM:cmche@hku.hken_US
dc.identifier.authorityChe, CM=rp00670en_US
dc.description.naturelink_to_subscribed_fulltexten_US
dc.identifier.doi10.1039/DT9910002933en_US
dc.identifier.scopuseid_2-s2.0-0342885908en_US
dc.identifier.issue11en_US
dc.identifier.spage2933en_US
dc.identifier.epage2939en_US
dc.identifier.isiWOS:A1991GR29800022-
dc.publisher.placeUnited Kingdomen_US
dc.identifier.scopusauthoridHo, C=23067224800en_US
dc.identifier.scopusauthoridLeung, WH=7201504510en_US
dc.identifier.scopusauthoridChe, CM=7102442791en_US

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