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Conference Paper: Hydrocarbon oxidation by β-halogenated dioxoruthenium(vi) porphyrin complexes: Effect of reduction potential (Ru VI/V) and C-H bond-dissociation energy on rate constants

TitleHydrocarbon oxidation by β-halogenated dioxoruthenium(vi) porphyrin complexes: Effect of reduction potential (Ru VI/V) and C-H bond-dissociation energy on rate constants
Authors
KeywordsElectrochemistry
Oxidation
Porphyrinoids
Ruthenium
Structure elucidation
Issue Date2005
PublisherWiley - V C H Verlag GmbH & Co KGaA. The Journal's web site is located at http://www.wiley-vch.de/home/chemistry
Citation
Chemistry - A European Journal, 2005, v. 11 n. 23, p. 7040-7053 How to Cite?
Abstract
β-Halogenated dioxoruthenium(VI) porphyrin complexes [Ru VI-(F 28-tpp)O 2] [F 28-tpp = 2,3,7,8,12,13, 17,18-octafluoro-5,10,15,20-tetrakis-(pentafluorophenyl)porphyrinato(2-)] and [Ru VI(β-Br 8-tmp)O 2] [β-Br 8-tmp = 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(2,4,6-trimethylphenyl) porphyrinato(2-)] were prepared from reactions of [Ru II(por)(CO)] [por = por-phyrinato(2-)] with m-chloroperoxybenzoic acid in CH 2Cl 2. Reactions of [Ru VI(por)O 2] with excess PPh 3 in CH 2Cl 2 gave [Ru II(F 20tpp)(PPh 3) 2] [F 20)-tpp = 5,10,15,20-tetrakis(pentafluo-rophenyl)porphyrinato(2-)] and [Ru II-(F 28-tpp)(PPh 3) 2]. The structures of [Ru II(por)(CO)(H 2O)] and [Ru II(por)-(PPh 3) 2] (por = F 20-tpp, F 28-tpp) were determined by X-ray crystallography, revealing the effect of β-fluorination of the porphyrin ligand on the coordination of axial ligands to ruthenium atom. The X-ray crystal structure of [Ru VI(F 20-tpp)O 2] shows a Ru=O bond length of 1.718(3) Å. Electrochemical reduction of [Ru VI(por)O 2] (Ru VI to Ru V) is irreversible or quasi-reversible, with the E p.c(Ru VI/V) spanning -0.31 to -1.15V versus Cp 2Fe +/0. Kinetic studies were performed for the reactions of various [Ru VI(por)O 2], including [Ru VI-(F 28-tpp)O 2] and [Ru VI(β-Br 8-tmp)O 2], with para-substituted styrenes p-X-C 6H 4CH=CH 2 (X = H, F, Cl, Me, MeO), cis- and trans-β-methylstyrene, cyclohexene, norbornene, ethylbenzene, cumene, 9,10-dihydroanthracene, xanthene, and fluorene. The second-order rate constants (k 2) obtained for the hydrocarbon oxidations by [Ru VI-(F 28-tpp)O 2] are up to 28-fold larger than by [Ru VI(F 20-tpp)O 2]. Dual-parameter Hammett correlation implies that the styrene oxidation by [Ru VI(F 28-tpp)O 2] should involve rate-limiting generation of a benzylic radical intermediate, and the spin delocalization effect is more important than the polar effect. The k 2 values for the oxidation of styrene and ethylbenzene by [Ru VI-(por)O 2] increase with E p.c(Ru VI/V), and there is a linear correlation between log k 2 and E p.c(Ru VI/V). The small slope (≈2 V -1) of the log k 2 versus E p.c(Ru VI/V) plot suggests that the extent of charge transfer is small in the rate-determining step of the hydrocarbon oxidations. The rate constants correlate well with the C-H bond dissociation energies, in favor of a hydrogen-atom abstraction mechanism. © 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
Persistent Identifierhttp://hdl.handle.net/10722/70148
ISSN
2013 Impact Factor: 5.696
ISI Accession Number ID
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Author Affiliations
  1. Institute of Molecular Technology for Drug Discovery and Synthesis, Hong Kong
  2. Hong Kong Polytechnic University
  3. Hong Kong University of Science and Technology
DC FieldValueLanguage
dc.contributor.authorChe, CMen_HK
dc.contributor.authorZhang, JLen_HK
dc.contributor.authorZhang, Ren_HK
dc.contributor.authorHuang, JSen_HK
dc.contributor.authorLai, TSen_HK
dc.contributor.authorTsui, WMen_HK
dc.contributor.authorZhou, XGen_HK
dc.contributor.authorZhou, ZYen_HK
dc.contributor.authorZhu, Nen_HK
dc.contributor.authorChang, CKen_HK
dc.date.accessioned2010-09-06T06:20:10Z-
dc.date.available2010-09-06T06:20:10Z-
dc.date.issued2005en_HK
dc.identifier.citationChemistry - A European Journal, 2005, v. 11 n. 23, p. 7040-7053en_HK
dc.identifier.issn0947-6539en_HK
dc.identifier.urihttp://hdl.handle.net/10722/70148-
dc.description.abstractβ-Halogenated dioxoruthenium(VI) porphyrin complexes [Ru VI-(F 28-tpp)O 2] [F 28-tpp = 2,3,7,8,12,13, 17,18-octafluoro-5,10,15,20-tetrakis-(pentafluorophenyl)porphyrinato(2-)] and [Ru VI(β-Br 8-tmp)O 2] [β-Br 8-tmp = 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(2,4,6-trimethylphenyl) porphyrinato(2-)] were prepared from reactions of [Ru II(por)(CO)] [por = por-phyrinato(2-)] with m-chloroperoxybenzoic acid in CH 2Cl 2. Reactions of [Ru VI(por)O 2] with excess PPh 3 in CH 2Cl 2 gave [Ru II(F 20tpp)(PPh 3) 2] [F 20)-tpp = 5,10,15,20-tetrakis(pentafluo-rophenyl)porphyrinato(2-)] and [Ru II-(F 28-tpp)(PPh 3) 2]. The structures of [Ru II(por)(CO)(H 2O)] and [Ru II(por)-(PPh 3) 2] (por = F 20-tpp, F 28-tpp) were determined by X-ray crystallography, revealing the effect of β-fluorination of the porphyrin ligand on the coordination of axial ligands to ruthenium atom. The X-ray crystal structure of [Ru VI(F 20-tpp)O 2] shows a Ru=O bond length of 1.718(3) Å. Electrochemical reduction of [Ru VI(por)O 2] (Ru VI to Ru V) is irreversible or quasi-reversible, with the E p.c(Ru VI/V) spanning -0.31 to -1.15V versus Cp 2Fe +/0. Kinetic studies were performed for the reactions of various [Ru VI(por)O 2], including [Ru VI-(F 28-tpp)O 2] and [Ru VI(β-Br 8-tmp)O 2], with para-substituted styrenes p-X-C 6H 4CH=CH 2 (X = H, F, Cl, Me, MeO), cis- and trans-β-methylstyrene, cyclohexene, norbornene, ethylbenzene, cumene, 9,10-dihydroanthracene, xanthene, and fluorene. The second-order rate constants (k 2) obtained for the hydrocarbon oxidations by [Ru VI-(F 28-tpp)O 2] are up to 28-fold larger than by [Ru VI(F 20-tpp)O 2]. Dual-parameter Hammett correlation implies that the styrene oxidation by [Ru VI(F 28-tpp)O 2] should involve rate-limiting generation of a benzylic radical intermediate, and the spin delocalization effect is more important than the polar effect. The k 2 values for the oxidation of styrene and ethylbenzene by [Ru VI-(por)O 2] increase with E p.c(Ru VI/V), and there is a linear correlation between log k 2 and E p.c(Ru VI/V). The small slope (≈2 V -1) of the log k 2 versus E p.c(Ru VI/V) plot suggests that the extent of charge transfer is small in the rate-determining step of the hydrocarbon oxidations. The rate constants correlate well with the C-H bond dissociation energies, in favor of a hydrogen-atom abstraction mechanism. © 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.en_HK
dc.languageengen_HK
dc.publisherWiley - V C H Verlag GmbH & Co KGaA. The Journal's web site is located at http://www.wiley-vch.de/home/chemistryen_HK
dc.relation.ispartofChemistry - A European Journalen_HK
dc.subjectElectrochemistryen_HK
dc.subjectOxidationen_HK
dc.subjectPorphyrinoidsen_HK
dc.subjectRutheniumen_HK
dc.subjectStructure elucidationen_HK
dc.titleHydrocarbon oxidation by β-halogenated dioxoruthenium(vi) porphyrin complexes: Effect of reduction potential (Ru VI/V) and C-H bond-dissociation energy on rate constantsen_HK
dc.typeConference_Paperen_HK
dc.identifier.openurlhttp://library.hku.hk:4550/resserv?sid=HKU:IR&issn=0947-6539&volume=11&issue=23&spage=7040&epage=7053&date=2005&atitle=Hydrocarbon+oxidation+by+β-halogenated+dioxoruthenium+(VI)+porphyrin+camplexes:+effect+of+reduction+potential+(RuVI/V)+and+C-H+bond-dissociation+energy+on+rate+constantsen_HK
dc.identifier.emailChe, CM: cmche@hku.hken_HK
dc.identifier.emailHuang, JS: jshuang@hku.hken_HK
dc.identifier.emailZhu, N: nzhu@hkucc.hku.hken_HK
dc.identifier.authorityChe, CM=rp00670en_HK
dc.identifier.authorityHuang, JS=rp00709en_HK
dc.identifier.authorityZhu, N=rp00845en_HK
dc.description.naturelink_to_subscribed_fulltext-
dc.identifier.doi10.1002/chem.200500814en_HK
dc.identifier.pmid16163758en_HK
dc.identifier.scopuseid_2-s2.0-27944472608en_HK
dc.identifier.hkuros117999en_HK
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-27944472608&selection=ref&src=s&origin=recordpageen_HK
dc.identifier.volume11en_HK
dc.identifier.issue23en_HK
dc.identifier.spage7040en_HK
dc.identifier.epage7053en_HK
dc.identifier.isiWOS:000233508800024-
dc.publisher.placeGermanyen_HK
dc.identifier.scopusauthoridChe, CM=7102442791en_HK
dc.identifier.scopusauthoridZhang, JL=7601341956en_HK
dc.identifier.scopusauthoridZhang, R=7404865969en_HK
dc.identifier.scopusauthoridHuang, JS=7407192639en_HK
dc.identifier.scopusauthoridLai, TS=7202203490en_HK
dc.identifier.scopusauthoridTsui, WM=36000681700en_HK
dc.identifier.scopusauthoridZhou, XG=7410094013en_HK
dc.identifier.scopusauthoridZhou, ZY=7406096262en_HK
dc.identifier.scopusauthoridZhu, N=7201449530en_HK
dc.identifier.scopusauthoridChang, CK=35242004200en_HK

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