File Download
There are no files associated with this item.
Links for fulltext
(May Require Subscription)
- Publisher Website: 10.1021/jo980755c
- Scopus: eid_2-s2.0-0001600921
- WOS: WOS:000076781600028
- Find via
Supplementary
- Citations:
- Appears in Collections:
Article: Mechanistic Investigation of the Oxidation of Aromatic Alkenes by Monooxoruthenium(IV). Asymmetric Alkene Epoxidation by Chiral Monooxoruthenium(IV) Complexes
Title | Mechanistic Investigation of the Oxidation of Aromatic Alkenes by Monooxoruthenium(IV). Asymmetric Alkene Epoxidation by Chiral Monooxoruthenium(IV) Complexes |
---|---|
Authors | |
Issue Date | 1998 |
Publisher | American Chemical Society. The Journal's web site is located at http://pubs.acs.org/joc |
Citation | Journal Of Organic Chemistry, 1998, v. 63 n. 22, p. 7715-7726 How to Cite? |
Abstract | The oxoruthenium(IV) complexes [RuIV(terpy)(6,6′-Cl2-bpy)O](ClO4) 2 (1a; terpy = 2,2′:6′,2″-terpyridine; 6,6′-Cl2-bpy = 6,6′-dichloro-2,2′-bipyridine), [RuIV(terpy)(tmeda)O](ClO4)2 (lb; tmeda = N,N,N′,N′-tetramethylethylenediamine), tRuIV(Cn)(bpy)O](ClO4)2 (1c; Cn = l,4,7-trimethyl-l,4,7-triazacyclononane), and [RuIV(PPz*Xbpy)O](ClO4)2 (Id; PPz* = 2,6-bis[(4S,7A)-7,8,8-trimethyl4,5,6,7-tetrahydro-4,7-methanoindazol-2-yl] pyridine) are effective for the epoxidation of aromatic alkenes in acetonitrile at ambient conditions. Their reactions with c/s-alkenes such as cis-β-methylstyrene and cis-β-deuteriostyrene afford epoxides nonstereospecifically. The observation of the inverse secondary kinetic isotope effect for the β-d2-styrene oxidations [kH/kD -0.87 (1b), 0.86 (Id)], but not for α-deuteriostyrene (kH/kD = 0.98 for lb and Id), indicates that C-O bond formation is more advanced at the β-carbon atom than at the a carbon, i.e., a stepwise mechanism. The second-order rate constants (k2) for the styrene oxidations are weakly dependent on the E°(RuIV/III) values of the oxoruthenium(IV) complexes, and both electron-withdrawing and -donating para substituents mildly accelerate the oxidation reaction of styrene. These findings discount strongly the intermediaries of an alkene-derived cation radical and a carbocation. A linear free-energy relationship between the second-order rate constants for the para-substituted styrene oxidations and the total substituent effect (TE) parameters has been established: (TE) = +0.43 (R = 0.99) for 1b, +0.50 (R = 0.98) for 1c, and +0.37 (R = 0.99) for Id (Wu, Y.-D.; Wong, C.-L.; Chan, K. W.; Ji, G.-Z.; Jiang, X.-K. J. Org. Chem. 1996, 61, 746). This suggests that the oxidation of aromatic alkenes by oxoruthenium(IV) complexes should proceed via the rate-limiting formation of a benzylic radical intermediate. Oxidation of styrene and cis- and trans-β-methylstyrenes by the chiral oxoruthenium (IV) complex Id attains moderate enantioselectivities, in which the production of cis-epoxide is more enantioselective than the trans counterpart. The ligand dissymmetry of PPz* together with the bipyridine ligand create a "chiral pocket" around the RuIV=O moiety, leading to enantiofacial discrimination through nonbonding interaction. Because the acyclic benzylic radical intermediate would undergo cis-trans isomerization before the second C-O bond formation, the overall product enantioselectivity (% eeobs) cannot be determined exclusively by facial selectivity (eefacial) of the first irreversible C-O bond formation step. The extent of the isomerization, measured by the cis-trans-epoxide selectivity or diastereoselectivity of epoxide ring closure, is an important element in controlling the enantiomeric excess of the epoxides. © 1998 American Chemical Society. |
Persistent Identifier | http://hdl.handle.net/10722/167355 |
ISSN | 2023 Impact Factor: 3.3 2023 SCImago Journal Rankings: 0.724 |
ISI Accession Number ID | |
References |
DC Field | Value | Language |
---|---|---|
dc.contributor.author | Fung, WH | en_US |
dc.contributor.author | Yu, WY | en_US |
dc.contributor.author | Che, CM | en_US |
dc.date.accessioned | 2012-10-08T03:05:59Z | - |
dc.date.available | 2012-10-08T03:05:59Z | - |
dc.date.issued | 1998 | en_US |
dc.identifier.citation | Journal Of Organic Chemistry, 1998, v. 63 n. 22, p. 7715-7726 | en_US |
dc.identifier.issn | 0022-3263 | en_US |
dc.identifier.uri | http://hdl.handle.net/10722/167355 | - |
dc.description.abstract | The oxoruthenium(IV) complexes [RuIV(terpy)(6,6′-Cl2-bpy)O](ClO4) 2 (1a; terpy = 2,2′:6′,2″-terpyridine; 6,6′-Cl2-bpy = 6,6′-dichloro-2,2′-bipyridine), [RuIV(terpy)(tmeda)O](ClO4)2 (lb; tmeda = N,N,N′,N′-tetramethylethylenediamine), tRuIV(Cn)(bpy)O](ClO4)2 (1c; Cn = l,4,7-trimethyl-l,4,7-triazacyclononane), and [RuIV(PPz*Xbpy)O](ClO4)2 (Id; PPz* = 2,6-bis[(4S,7A)-7,8,8-trimethyl4,5,6,7-tetrahydro-4,7-methanoindazol-2-yl] pyridine) are effective for the epoxidation of aromatic alkenes in acetonitrile at ambient conditions. Their reactions with c/s-alkenes such as cis-β-methylstyrene and cis-β-deuteriostyrene afford epoxides nonstereospecifically. The observation of the inverse secondary kinetic isotope effect for the β-d2-styrene oxidations [kH/kD -0.87 (1b), 0.86 (Id)], but not for α-deuteriostyrene (kH/kD = 0.98 for lb and Id), indicates that C-O bond formation is more advanced at the β-carbon atom than at the a carbon, i.e., a stepwise mechanism. The second-order rate constants (k2) for the styrene oxidations are weakly dependent on the E°(RuIV/III) values of the oxoruthenium(IV) complexes, and both electron-withdrawing and -donating para substituents mildly accelerate the oxidation reaction of styrene. These findings discount strongly the intermediaries of an alkene-derived cation radical and a carbocation. A linear free-energy relationship between the second-order rate constants for the para-substituted styrene oxidations and the total substituent effect (TE) parameters has been established: (TE) = +0.43 (R = 0.99) for 1b, +0.50 (R = 0.98) for 1c, and +0.37 (R = 0.99) for Id (Wu, Y.-D.; Wong, C.-L.; Chan, K. W.; Ji, G.-Z.; Jiang, X.-K. J. Org. Chem. 1996, 61, 746). This suggests that the oxidation of aromatic alkenes by oxoruthenium(IV) complexes should proceed via the rate-limiting formation of a benzylic radical intermediate. Oxidation of styrene and cis- and trans-β-methylstyrenes by the chiral oxoruthenium (IV) complex Id attains moderate enantioselectivities, in which the production of cis-epoxide is more enantioselective than the trans counterpart. The ligand dissymmetry of PPz* together with the bipyridine ligand create a "chiral pocket" around the RuIV=O moiety, leading to enantiofacial discrimination through nonbonding interaction. Because the acyclic benzylic radical intermediate would undergo cis-trans isomerization before the second C-O bond formation, the overall product enantioselectivity (% eeobs) cannot be determined exclusively by facial selectivity (eefacial) of the first irreversible C-O bond formation step. The extent of the isomerization, measured by the cis-trans-epoxide selectivity or diastereoselectivity of epoxide ring closure, is an important element in controlling the enantiomeric excess of the epoxides. © 1998 American Chemical Society. | en_US |
dc.language | eng | en_US |
dc.publisher | American Chemical Society. The Journal's web site is located at http://pubs.acs.org/joc | en_US |
dc.relation.ispartof | Journal of Organic Chemistry | en_US |
dc.title | Mechanistic Investigation of the Oxidation of Aromatic Alkenes by Monooxoruthenium(IV). Asymmetric Alkene Epoxidation by Chiral Monooxoruthenium(IV) Complexes | en_US |
dc.type | Article | en_US |
dc.identifier.email | Che, CM:cmche@hku.hk | en_US |
dc.identifier.authority | Che, CM=rp00670 | en_US |
dc.description.nature | link_to_subscribed_fulltext | en_US |
dc.identifier.doi | 10.1021/jo980755c | - |
dc.identifier.scopus | eid_2-s2.0-0001600921 | en_US |
dc.identifier.hkuros | 40261 | - |
dc.relation.references | http://www.scopus.com/mlt/select.url?eid=2-s2.0-0001600921&selection=ref&src=s&origin=recordpage | en_US |
dc.identifier.volume | 63 | en_US |
dc.identifier.issue | 22 | en_US |
dc.identifier.spage | 7715 | en_US |
dc.identifier.epage | 7726 | en_US |
dc.identifier.isi | WOS:000076781600028 | - |
dc.publisher.place | United States | en_US |
dc.identifier.scopusauthorid | Fung, WH=7102150303 | en_US |
dc.identifier.scopusauthorid | Yu, WY=7403913673 | en_US |
dc.identifier.scopusauthorid | Che, CM=7102442791 | en_US |
dc.identifier.issnl | 0022-3263 | - |