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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?
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.
Persistent Identifierhttp://hdl.handle.net/10722/70148
ISSN
2014 Impact Factor: 5.731
2014 SCImago Journal Rankings: 2.234
ISI Accession Number ID
References

 

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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