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

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Title	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
Authors	Che, CM1 Zhang, JL1 Zhang, R1 Huang, JS1 Lai, TS3 Tsui, WM1 Zhou, XG1 Zhou, ZY2 Zhu, N1 Chang, CK3
Keywords	Electrochemistry Oxidation Porphyrinoids Ruthenium Structure elucidation
Issue Date	2005
Publisher	Wiley - 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?] DOI: http://dx.doi.org/10.1002/chem.200500814
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.
ISSN	0947-6539 2011 Impact Factor: 5.925 2011 SCImago Journal Rankings: 0.455
DOI	http://dx.doi.org/10.1002/chem.200500814
ISI Accession Number ID	WOS:000233508800024
References	References in Scopus

DC Field	Value
dc.contributor.author	Che, CM
dc.contributor.author	Zhang, JL
dc.contributor.author	Zhang, R
dc.contributor.author	Huang, JS
dc.contributor.author	Lai, TS
dc.contributor.author	Tsui, WM
dc.contributor.author	Zhou, XG
dc.contributor.author	Zhou, ZY
dc.contributor.author	Zhu, N
dc.contributor.author	Chang, CK
dc.date.accessioned	2010-09-06T06:20:10Z
dc.date.available	2010-09-06T06:20:10Z
dc.date.issued	2005
dc.description.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.
dc.description.nature	Link_to_subscribed_fulltext
dc.identifier.citation	Chemistry - A European Journal, 2005, v. 11 n. 23, p. 7040-7053 [How to Cite?] DOI: http://dx.doi.org/10.1002/chem.200500814
dc.identifier.doi	http://dx.doi.org/10.1002/chem.200500814
dc.identifier.epage	7053
dc.identifier.hkuros	117999
dc.identifier.isi	WOS:000233508800024
dc.identifier.issn	0947-6539 2011 Impact Factor: 5.925 2011 SCImago Journal Rankings: 0.455
dc.identifier.issue	23
dc.identifier.openurl
dc.identifier.pmid	16163758
dc.identifier.scopus	eid_2-s2.0-27944472608
dc.identifier.spage	7040
dc.identifier.uri	http://hdl.handle.net/10722/70148
dc.identifier.volume	11
dc.language	eng
dc.publisher	Wiley - V C H Verlag GmbH & Co KGaA. The Journal's web site is located at http://www.wiley-vch.de/home/chemistry
dc.publisher.place	Germany
dc.relation.ispartof	Chemistry - A European Journal
dc.relation.references	References in Scopus
dc.subject	Electrochemistry
dc.subject	Oxidation
dc.subject	Porphyrinoids
dc.subject	Ruthenium
dc.subject	Structure elucidation
dc.title	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
dc.type	Conference_Paper

<?xml encoding="utf-8" version="1.0"?><item><contributor.author>Che, CM</contributor.author><contributor.author>Zhang, JL</contributor.author><contributor.author>Zhang, R</contributor.author><contributor.author>Huang, JS</contributor.author><contributor.author>Lai, TS</contributor.author><contributor.author>Tsui, WM</contributor.author><contributor.author>Zhou, XG</contributor.author><contributor.author>Zhou, ZY</contributor.author><contributor.author>Zhu, N</contributor.author><contributor.author>Chang, CK</contributor.author><date.accessioned>2010-09-06T06:20:10Z</date.accessioned><date.available>2010-09-06T06:20:10Z</date.available><date.issued>2005</date.issued><identifier.citation>Chemistry - A European Journal, 2005, v. 11 n. 23, p. 7040-7053</identifier.citation><identifier.issn>0947-6539</identifier.issn><identifier.uri>http://hdl.handle.net/10722/70148</identifier.uri><description.abstract>&#946;-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(&#946;-Br 8-tmp)O 2] [&#946;-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 &#946;-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) &#197;. 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(&#946;-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-&#946;-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 (&#8776;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. &#169; 2005 Wiley-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.</description.abstract><language>eng</language><publisher>Wiley - V C H Verlag GmbH &amp; Co KGaA. 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Author Affiliations

Institute of Molecular Technology for Drug Discovery and Synthesis, Hong Kong
Hong Kong Polytechnic University
Hong Kong University of Science and Technology

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

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