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Chi-Ming Che

Publications and source records attributed to Chi-Ming Che.

120 records · Page 7Linked to original sources
PubMed2002

Dendritic ruthenium porphyrins: a new class of highly selective catalysts for alkene epoxidation and cyclopropanation.

Attachment of Fréchet-type poly(benzyl ether) dendrons [G-n] to carbonylruthenium(II) meso-tetraphenylporphyrin (5) using covalent etheric bonds forms a series of dendritic ruthenium(II) porphyrins 5-[G-n](m) (m=4, n=1, 2; m=8, n=0-2). The attachment was realized by treating the carbonylruthenium(II) complex of 5,10,15,20- tetrakis(4'-hydroxyphenyl)porphyrin or 5,10,15,20-tetrakis(3',5'-dihydroxyphenyl)porphyrin with [G-n]OSO(2)Me in refluxing dry acetone in the presence of potassium carbonate and [18]crown-6. Complexes 5-[G-n](m) were characterized by UV/Vis, IR, and NMR spectroscopy and mass spectrometry. All of the dendritic ruthenium porphyrins are highly selective catalysts for epoxidation of alkenes with 2,6-dichloropyridine N-oxide (Cl(2)pyNO). The chemo- or diastereoselectivity increases with the generation number of the dendron and the number of dendrons attached to 5, and complex 5-[G-2](8) exhibits remarkable selectivity or turnover number in catalyzing the Cl(2)pyNO epoxidation of a variety of alkene substrates including styrene, trans-/cis-stilbene, 2,2-dimethylchromene, cyclooctene, and unsaturated steroids such as cholesteryl esters and estratetraene derivative. The cyclopropanation of styrene and its para-substituted derivatives with ethyl diazoacetate catalyzed by 5-[G-2](8) is highly trans selective.

Alkenes↗
PubMed2002

Metalloporphyrin-mediated asymmetric nitrogen-atom transfer to hydrocarbons: aziridination of alkenes and amidation of saturated C-H bonds catalyzed by chiral ruthenium and manganese porphyrins.

Chiral metalloporphyrins [Mn(Por*)(OH)(MeOH)] (1) and [Ru(Por*)(CO)(EtOH)] (2) catalyze asymmetric aziridination of aromatic alkenes and asymmetric amidation of benzylic hydrocarbons to give moderate enantiomeric excesses. The mass balance in these nitrogen-atom-transfer processes has been examined. With PhI=NTs as the nitrogen source, the aziridination of styrenes, trans-stilbene, 2-vinylnaphthalene, indene, and 2,2-dimethylchromene catalyzed by complex 1 or 2 resulted in up to 99 % substrate conversions and up to 94 % aziridine selectivities, whereas the amidation of ethylbenzenes, indan, tetralin, 1-, and 2-ethylnaphthalene catalyzed by complex 2 led to substrate conversions of up to 32 % and amide selectivities of up to 91 %. Complex 1 or 2 can also catalyze the asymmetric amidation of 4-methoxyethylbenzene, tetralin, and 2-ethylnaphthalene with "PhI(OAc)(2) + NH(2)SO(2)Me", affording the N-substituted methanesulfonamides in up to 56 % ee with substrate conversions of up to 34 % and amide selectivities of up to 92 %. Extension of the "complex 1 + PhI=NTs" or "complex 1 + PhI(OAc)(2) + NH(2)R (R=Ts, Ns)" amidation protocol to a steroid resulted in diastereoselective amidation of cholesteryl acetate at the allylic C-H bonds at C-7 with substrate conversions of up to 49 % and amide selectivities of up to 90 % (alpha:beta ratio: up to 4.2:1). An aziridination- and amidation-active chiral bis(tosylimido)ruthenium(VI) porphyrin, [Ru(Por*)(NTs)(2)] (3), and a ruthenium porphyrin aziridine adduct, [Ru(Por*)(CO)(TsAz)] (4, TsAz=N-tosyl-2- (4-chlorophenyl)aziridine), have been isolated from the reaction of 2 with PhI=NTs and N-tosyl-2-(4-chlorophenyl)aziridine, respectively. The imidoruthenium porphyrin 3 could be an active species in the aziridination or amidation catalyzed by complex 2 described above. The second-order rate constants for the reactions of 3 with styrenes, 2-vinylnaphthalene, indene, ethylbenzenes, and 2-ethylnaphthalene range from 3.7-42.5x10(-3) dm(3) mol(-1) s(-1). An X-ray structure determination of complex 4 reveals an O- rather than N-coordination of the aziridine axial ligand. The fact that the N-tosylaziridine in 4 does not adopt an N-coordination mode disfavors a concerted pathway in the aziridination by a tosylimido ruthenium porphyrin active species.

Alkenes↗
PubMed2002

Ruthenium(II) porphyrin catalyzed formation of (Z)-4-alkyloxycarbonyl- methylidene-1,3-dioxolanes from gamma-alkoxy-alpha-diazo-beta-ketoesters.

[reaction: see text] Ruthenum(II) porphyrins and dirhodium(II) acetate catalyze cyclization of gamma-alkoxy-alpha-diazo-beta-ketoesters to (Z)-4-(alkyloxycarbonylmethylidene)-1,3-dioxolanes selectively (ca. 68% yield) with no formation of 3(2H)-furanones. Reacting a diazo ketoester with [Ru(II)(TTP)(CO)] [H(2)TTP = meso-tetrakis(p-tolyl) porphyrin] in toluene afforded a ruthenium carbenoid complex, which has been isolated and spectroscopically characterized. A mechanism involving hydrogen atom migration from the C-H bond to the ruthenium carbenoid is proposed.

Journal Article↗
PubMed2002

[(C(wedge)N(wedge)N)Pt(C identical to C)nR] (HC(wedge)N(wedge)N = 6-aryl-2,2'-bipyridine, n = 1-4, R = aryl, SiMe3) as a new class of light-emitting materials and their applications in electrophosphorescent devices.

Tridentate cyclometalated platinum(II) complexes bearing sigma-alkynyl ligands exhibit tunable photoluminescence and enhanced stability during vacuum deposition; OLEDs based on these materials display orange to red electrophosphorescence with low turn-on voltages (approximately 4 V), maximum luminance approaching 10,000 cd m-2 and efficiency up to 4.2 cd A-1.

Journal Article↗
PubMed1998

Synthesis, Spectroscopic Properties, and Reactivities of Bis(tosylimido)osmium(VI) Porphyrin Complexes. X-ray Crystal Structure of [Os(VI)(TPP)(NSO(2)C(6)H(4)-pCH(3))(2)] (TPP = Tetraphenylporphyrinato).

The bis(tosylimido)osmium(VI) porphyrins [Os(VI)(Por)(NTs)(2)] [Por = tetraphenylporphyrinato (TPP), meso-tetrakis(p-tolyl)porphyrinato (TTP), meso-tetrakis(4-chlorophenyl)porphyrinato (4-Cl-TPP), meso-tetrakis(4-methoxyphenyl)porphyrinato (4-MeO-TPP); Ts = tosyl] were prepared from the reactions of [Os(II)(Por)(CO)(MeOH)] with excess PhI=NTs in dichloromethane. The X-ray crystal structure of [Os(VI)(TPP)(NTs)(2)] has been determined. Crystal data for [Os(VI)(TPP)(NTs)(2)]: triclinic, space group P&onemacr; (No. 2), a = 10.836(3) Å, b = 12.067(4) Å, c = 19.647(6) Å, alpha = 94.05(3) degrees, beta = 93.88(3) degrees, gamma = 104.65(3) degrees, V = 2469(1) Å(3), Z = 2, R (R(w)) = 0.030 (0.038), goodness-of-fit = 1.19. The mean Os=NTs distance is 1.800 Å. The Os-N-S angles average 155.8 degrees. Reaction of [Os(VI)(TPP)(NTs)(2)] with triphenylphosphine gives Ph(3)P=NTs and [Os(II)(TPP)(PPh(3))(2)].

Journal Article↗
PubMed1998

Ruthenium meso-Tetrakis(2,6-dichlorophenyl)porphyrin Complex Immobilized in Mesoporous MCM-41 as a Heterogeneous Catalyst for Selective Alkene Epoxidations.

A ruthenium complex of meso-tetrakis(2,6-dichlorophenyl)porphyrin, [Ru(II)(TDCPP)(CO)(EtOH)], is immobilized into mesoporous MCM-41 molecular sieves; the supported Ru catalyst can effect highly selective heterogeneous alkene epoxidations using 2,6-dichloropyridine N-oxide as terminal oxidant. Aromatic and aliphatic alkenes can be efficiently converted to their epoxides in good yields and selectivities, and cis-alkenes such as cis-stilbene, cis-beta-methylstyrene, and cis-beta-deuteriostyrene are epoxidized stereospecifically. Oxidation of cycloalkenes, e.g., norbornene and cyclooctene, can be carried out effectively using the heterogeneous Ru-catalyzed reaction while these alkenes are unreactive in the zeolite-based titanium silicate (TS-1)-catalyzed conditions (Murugavel, R.; Roesky, H. W. Angew. Chem., Int. Ed. Engl. 1997, 36, 477). On the other hand, the Ru/M-41(m) catalyst displays size selectivity in the (+)-limonene oxidation where the terminal C=C bond (vs internal trisubstituted C=C bond) becomes more readily oxidized. Bulky 3,4,6-tri-O-benzyl-D-glucal has failed to react under the heterogeneous Ru-catalyzed conditions, whereas the smaller acetyl derivative is converted to a 3:1 mixture of alpha- and beta-glycal epoxides. The Ru/M-41(m) catalyst can be used repeatedly, and 67% of its initial activity is retained after 11 691 turnovers (three runs). The loss of activity is attributed to catalyst leaching and/or deactivation. On the basis of Hammett correlation (rho(+) = -0.72, R = 0.997) and product studies (cyclohexene and cis-alkenes as the substrates), a reactive dioxoruthenium(VI) porphyrin intermediate is not favored. An oxoruthenium(V) complex or oxoruthenium(IV) porphyrin cation radical could be the key intermediate for this highly selective epoxidation reaction.

Journal Article↗
PubMed1997

Synthesis of Bis(aliphatic amine)osmium(II), Bis(arylamido)osmium(IV), and Bis(imido)- and Oxo(imido)osmium(VI) Porphyrins.

The syntheses, characterization, and reactivity of a series of osmium porphyrins, Os(II)(Por)(H(2)NR)(2) [Por = dianions of octaethylporphyrinato (OEP), tetraphenylporphyrinato (TPP), meso-tetrakis(p-tolyl)porphyrinato (TTP), meso-tetrakis(4-chlorophenyl)porphyrinato (4-Cl-TPP), meso-tetrakis(3,4,5-trimethoxyphenyl)porphyrinato (3,4,5-MeO-TPP), R = (t)Bu; Por = TPP, R = (i)Pr], Os(II)(Por)(HNEt(2))(2) (Por = TPP, 3,4,5-MeO-TPP), Os(IV)(Por)(NHAr)(2) (Por = OEP, TPP, 3,4,5-MeO-TPP; Ar = Ph, 4-F-Ph), Os(VI)(Por)(N(t)Bu)(2) (Por = TPP, TTP, 4-Cl-TPP, 3,4,5-MeO-TPP), Os(VI)O(Por)(N(t)Bu) (Por = TPP, TTP, 4-Cl-TPP, 3,4,5-MeO-TPP), and Os(VI)O(Por)(4-F-PhN) (Por = TPP, 3,4,5-MeO-TPP) are described. The complexes Os(Por)(HNAr)(2) are prepared from the reactions of Os(Por)(N(2))(THF) with arylamines in aerobic tetrahydrofuran. Air oxidations of Os(Por)(H(2)N(t)Bu)(2) in tetrahydrofuran and in the presence of H(2)N(t)Bu give OsO(Por)(N(t)Bu) and Os(Por)(N(t)Bu)(2). The X-ray crystal structures of OsO(TTP)(N(t)Bu).EtOH and Os(4-Cl-TPP)(N(t)Bu)(2) have been determined. Crystal data for OsO(TTP)(N(t)Bu).EtOH: monoclinic, space group P2(1)/c, a = 13.546(6) Å, b = 23.180(3) Å, c = 16.817(3) Å, beta = 90.84(2) degrees, V = 5279.7(1.0) Å(3), Z = 4. Os(4-Cl-TPP)(N(t)Bu)(2): monoclinic, space group P2(1)/c, a = 11.046(2) Å, b = 18.380(3) Å, c = 23.640(4) Å, beta = 97.22(1) degrees, V = 4759.8(1.0) Å(3), Z = 4. The Os=O and Os=N(t)Bu distances in OsO(TTP)(N(t)Bu).EtOH are 1.772(7) and 1.759(9) Å, respectively. The Os=N(t)Bu distances in Os(4-Cl-TPP)(N(t)Bu)(2) average 1.775 Å. The imido angles range from 165.8(8) to 170.6(9) degrees. For the infrared spectra of these complexes, a discussion on the "oxidation state marker" band in the vicinity of 1000 cm(-)(1) is presented. The differences in the electronic properties of osmium porphyrins at various oxidation states are also described.

Journal Article↗
PubMed1996

Bis(amido)ruthenium(IV) Complexes with 2,3-Diamino-2,3-dimethylbutane. Crystal Structure and Reversible Ru(IV)-Amide/Ru(III)-Amine and Ru(IV)-Amide/Ru(II)- Amine Redox Couples in Aqueous Solution.

Two bis(amido)ruthenium(IV) complexes, [Ru(IV)(bpy)(L-H)(2)](2+) and [Ru(IV)(L)(L-H)(2)](2+) (bpy = 2,2'-bipyridine, L = 2,3-diamino-2,3-dimethylbutane, L-H = (H(2)NCMe(2)CMe(2)NH)(-)), were prepared by chemical oxidation of [Ru(II)(bpy)(L)(2)](2+) and the reaction of [(n-Bu)(4)N][Ru(VI)NCl(4)] with L, respectively. The structures of [Ru(bpy)(L-H)(2)][ZnBr(4)].CH(3)CN and [Ru(L)(L-H)(2)]Cl(2).2H(2)O were determined by X-ray crystal analysis. [Ru(bpy)(L-H)(2)][ZnBr(4)].CH(3)CN crystallizes in the monoclinic space group P2(1)/n with a = 12.597(2) Å, b = 15.909(2) Å, c = 16.785(2) Å, beta = 91.74(1) degrees, and Z = 4. [Ru(L)(L-H)(2)]Cl(2).2H(2)O crystallizes in the tetragonal space group I4(1)/a with a = 31.892(6) Å, c = 10.819(3) Å, and Z = 16. In both complexes, the two Ru-N(amide) bonds are cis to each other with bond distances ranging from 1.835(7) to 1.856(7) Å. The N(amide)-Ru-N(amide) angles are about 110 degrees. The two Ru(IV) complexes are diamagnetic, and the chemical shifts of the amide protons occur at around 13 ppm. Both complexes display reversible metal-amide/metal-amine redox couples in aqueous solution with a pyrolytic graphite electrode. Depending on the pH of the media, reversible/quasireversible 1e(-)-2H(+) Ru(IV)-amide/Ru(III)-amine and 2e(-)-2H(+) Ru(IV)-amide/Ru(II)-amine redox couples have been observed. At pH = 1.0, the E degrees is 0.46 V for [Ru(IV)(bpy)(L-H)(2)](2+)/[Ru(III)(bpy)(L)(2)](3+) and 0.29 V vs SCE for [Ru(IV)(L)(L-H)(2)](2+)/[Ru(III)(L)(3)](3+). The difference in the E degrees values for the two Ru(IV)-amide complexes has been attributed to the fact that the chelating saturated diamine ligand is a better sigma-donor than 2,2'-bipyridine.

Journal Article↗
PubMedDate not supplied

Neuroprotective effects of anti-aging oriental medicine Lycium barbarum against beta-amyloid peptide neurotoxicity.

As aged population dramatically increases in these decades, efforts should be made on the intervention for curing age-associated neurodegenerative diseases such as Alzheimer's disease (AD). Natural plant extracts of Lycium barbarum are well-known to exhibit anti-aging effects. We therefore hypothesized that they exhibit neuroprotective effects against toxins in aging-related neurodegenerative diseases. In this study, we aimed to investigate whether extracts from L. barbarum have neuroprotective effects against toxicity of fibrillar Abeta(1-42) and Abeta(25-35) fragments. Primary rat cortical neurons exposed to Abeta peptides resulted in apoptosis and necrosis. Pre-treatment with extract isolated from L. barbarum significantly reduced the release of lactate dehydrogenase (LDH). In addition, it attenuated Abeta peptide-activated caspases-3-like activity. The extract elicited a typical dose-dependent neuroprotective effect. Effective dosage of this extract was wider than that of a well-known western neuroprotective medicine lithium chloride (LiCl). We have further examined the underlying mechanisms of the neuroprotective effects. In agreement with other laboratories, Abeta peptides induce a rapid activation of c-Jun N-terminal kinase (JNK) by phosphorylation. Pre-treatment of aqueous extract markedly reduced the phosphorylation of JNK-1 (Thr183/Tyr185) and its substrates c-Jun-I (Ser 73) and c-Jun-II (Ser 63). Taken together, we have proved our hypothesis by showing neuroprotective effects of the extract from L. barbarum. Study on anti-aging herbal medicine like L. barbarum may open a new therapeutic window for the prevention of AD.

Alzheimer Disease↗