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1.
Axially chiral C2-symmetric N-heterocyclic carbene (NHC) palladium diaquo complexes 1a and 1b, derived from (R)-BINAM, are effective catalysts for the enantioselective α-hydroxylation of β-keto esters using oxaziridine 2a as the oxidant to give the corresponding products in high yields along with moderate enantioselectivities. 相似文献
2.
A chiral C2-symmetric NCN ligand, (5R,7R)-1,3-bis(6,6-dimethyl-5,6,7,8-tetrahydro-5,7-methanoquinolin-2-yl)benzene has been synthesized. A direct cyclometalation of this ligand with K2MCl4 (M = Pt, Pd) in dry acetic acid offered the corresponding pincer complexes, [(5R,7R)-1,3-bis(6,6-dimethyl-5,6,7,8-tetrahydro-5,7-methanoquinolin-2-yl)phenyl]platinum(II) chloride 5a and its palladium(II) analogue 5b. The Pt(II) and Pd(II) complexes 5 were characterized by NMR spectroscopy, and X-ray crystal structure analysis was done for the Pt(II) complex. The NMR data for both the complexes and X-ray crystal structural data for the chloro-Pt(II) complex indicate the existence of intramolecular C-H?Cl hydrogen bonding both in solution and in solid states. Chloride abstraction from 5a by treatment with silver triflate resulted in the corresponding triflate complex 6a, which generates the corresponding cationic aqua complex 7a in the presence of water molecules. The Pt(II) complex 6a/7a was used as asymmetric catalyst in the aldol reaction between methyl isocyanoacetate and aldehydes and also in the silylcyanation of aldehydes. 相似文献
3.
Manabu Hatano 《Tetrahedron letters》2008,49(2):379-382
The enantioselective alkynylation of aldimines with terminal acetylenes catalyzed by chiral Cu(I) complexes with (R)-2,2′-di(2-aminoaryloxy)-1,1′-binaphthyl ligands (7) was examined. Chiral C2-symmetric N,N-ligands 7, which have primary aniline moieties, were readily prepared from inexpensive (R)-1,1′-binaphthol (BINOL) as a chiral source. In particular, the reaction of N-benzylidenebenzeneamine 1a with phenylacetylene 2a proceeded smoothly in the presence of 5 mol % of (CuOTf)2·C6H5CH3 and 10 mol % of (R)-7d at room temperature for 24 h, and the corresponding propargylamine 3a was obtained with up to 82% ee. 相似文献
4.
《Journal of molecular catalysis. A, Chemical》1998,128(1-3):29-39
The Cs- and C2v-symmetric doubly dimethylsilylene-bridged zirconocene complexes (Me2Si)2{η5-C5H2-4-CHMe2}{η5-C5H-3,5-(SiMe3)2}ZrCl2, 6a, and (Me2Si)2{η5-C5H-3,5-(CHMe2)2}2ZrCl2, 6b, have been synthesized by reaction of corresponding dilithio ligand salts with ZrCl4 in CH2Cl2. When activated with methyl aluminoxane, Cs-symmetric zirconocene 6a catalyzes the polymerization of propylene (liquid propylene, 0°C) to yield a syndiotactic polymer of Mw=1,000,000 and rrrr%=75.4. By contrast, C2v-symmetric zirconocene 6b displays a low activity and affords an atactic polymer. 相似文献
5.
《Tetrahedron: Asymmetry》1999,10(10):1935-1945
Chiral derivatives of 2,4,5,6-tetrachloro-1,3-dicyanobenzene 1 with one, two and three (R)-1-phenylethylamino ((R)-PEA) units 2–4 are prepared and their chiroptical and conformational properties discussed on the bases of the UV/CD, NMR and MM2 data. High polarity of the persubstituted benzene ring leads to peculiar UV and IR spectra of achiral model compounds 5–7, whereas relatively rigid conformations of the chiral analogues 2–4 are reflected in the CD spectra. Strong exciton coupling (EC) appears in the CD spectrum of pseudo-C3-symmetric 4; this type of interaction seems not to be present in the C1-symmetric 2 and C2-symmetric 3. The absence of a molecular cleft in the chiral structures 2–4 could explain their inability to recognise the enantiomers of some racemates in the NMR experiment. 相似文献
6.
Misako NakamuraTakuya Taniguchi Naohisa IshidaKeishi Hayashi Masahiro MuraokaYohji Nakatsuji 《Tetrahedron》2011,67(48):9298-9304
Kinetic resolution of a racemic mixture of C2-symmetric 18-crown-6 diols (rac-1a) and 15-crown-5 diol (rac-1c) was achieved by lipase-catalyzed acetylation. The enantiomeric excess of the chiral crown diols (95% ee and 82% ee) was determined by 1H NMR spectroscopy, using (R)-(+)-1-(1-naphthyl)ethylammonium hydrochloride as a shift reagent. The C2-symmetric chiral 15-crown-5 diol (>95% ee) was also obtained by kinetic resolution of the racemic diacetate (rac-2c) using lipase-catalyzed solvolysis. 相似文献
7.
《Tetrahedron: Asymmetry》2001,12(23):3313-3317
A practical regioselective sulfenylation reaction of the achiral title compound 1 provides desymmetrization and access to C2-symmetric sulphur derivatives. Resolution of 2,2′,6,6′-tetramethoxy-3,3′-dimercapto-1,1′-biphenyl 7 was achieved by conversion to the corresponding dithiocarbonate diastereomers. The absolute configuration of (aR)-(−)-7 and (aS)-(+)-7 was assigned unambiguously. 相似文献
8.
Antonio Venegas Lucrecia Rivas Gabriela Huelgas Cecilia Anaya de Parrodi Domingo Madrigal Gerardo Aguirre Miguel Parra-Hake Daniel Chvez Ratnasamy Somanathan 《Tetrahedron: Asymmetry》2010,21(24):1257-2948
A series of chiral C2-symmetric tetrakis(sulfonamides) 3a–f, 4a–f were prepared and employed as ligands for titanium(IV) complexes in the asymmetric addition of diethylzinc to benzaldehyde. The chiral secondary alcohols were obtained in high yields and in moderate enantioselectivities. 相似文献
9.
Denis A Kissounko 《Journal of organometallic chemistry》2003,683(1):29-38
Protonation of the trimethylenemethane derivatives, Cp*Zr(σ2,π-C4H6)[N(R1)C(Me)N(R2)] (1a: R1=R2=i-Pr and 1b: R1=Et, R2=t-Bu) (Cp*=η5-C5Me5), by [PhNMe2H][B(C6F5)4] in chlorobenzene at −10 °C provides the cationic methallyl complexes, Cp*Zr(η3-C4H7)[N(R1)C(Me)N(R2)] (2a: R1=R2=i-Pr and 2b: R1=Et, R2=t-Bu), which are thermally robust in solution at elevated temperatures as determined by 1H NMR spectroscopy. Addition of B(C6F5)3 to 1a and 1b provides the zwitterionic allyl complexes, Cp*Zr{η3-CH2C[CH2B(C6F5)3]CH2}[N(R1)C(Me)N(R2)] (3a: R1=R2=i-Pr and 3b: R1=Et, R2=t-Bu). The crystal structures of 2b and 3a have been determined. Neither the cationic complexes 2 or the zwitterionic complexes 3 are active initiators for the Ziegler-Natta polymerization of ethylene and α-olefins. 相似文献
10.
《Tetrahedron: Asymmetry》2007,18(5):645-650
Chiral C2-symmetric diphenylthiophosphoramide ligand L1 prepared from C2-symmetric (1S,2S)-(−)-1,2-diphenylethylenediamine was found to be a fairly effective chiral ligand for Cu(I)-promoted 1,3-dipolar cycloaddition of imines and pyrrole-2,5-dione derivatives to give the corresponding adducts in moderate enantioselectivities and good yields. 相似文献
11.
Abdel-Sattar S. Hamad Elgazwy 《Polyhedron》2009,28(17):3667-3674
3-(2-Chloroquinolin-3-yl)-1,5-bis(3,4,5-trimethoxy-phenyl)-pentane-2,4-dione derivatives 3a–b were conveniently synthesized in excellent yields (82% each) by tandem Knoevenagel condensation reactions of 2-chloro-3-carbaldehyde-quinoline 1a–b with 3,4,5-trimethoxy acetophenone, followed by a base catalyzed Michael addition, such as DBU (1,8-diazabicyclo[5,4,0]undec-7-ene) with or without solvent. The reactions of 3a–b with Pd(dba)2 in the presence of PPh3 (1:2) in degassed acetone provided the dinuclear palladium complexes {Pd(C,N-2-C9H4N–CH–[–CH2CO(3,4,5-(OMe-)3–C6H2-]2–3-R-6)Cl(PPh3)}2 [(R = H (4a), R = OMe (4b)] in moderate yields (38% and 43%), which in turn reacted with an excess of isonitrile XyNC (Xy = 2,6-Me2C6H3) to give the corresponding palladacycles 5a–b in moderate yields (45% and 43%). The palladacycles 5a–b were also obtained in similar yields (32% and 33%) via a one-pot oxidative addition reaction of 3a-b with isonitrile XyNC:Pd(dba)2 (4:1). The products were characterized by satisfactory elemental analysis and spectral studies (IR, 1H, and 31P NMR). The crystal structure of 5a was determined by X-ray crystallography diffraction studies. 相似文献
12.
V. Crocq J. -C. Daran M. Gouygou B. Heim Y. Jeannin R. Speel 《Journal of Cluster Science》1996,7(4):505-529
The diiron ynamine complex [Fe2(CO)7{μ-CR)C(NEt2)}] (1:R=Me,2:R = C3H5.3:R=SiMe3.4:R = Ph) reacts at room temperature with diphenyldiazomethane Ph2CN2, in hexane to yield complexes [Fe2(CO)6{C(R)C(NEt2)N (NCPh2)] (5a:R=Me,6a:R=C3H5.7a R=SiMe3.8a:R=Ph) resulting from the insertion of the terminal nitrogen atom into the Fe=C carbene bond. Insertion the second nitrogen atom and formation of compounds [Fe2(CO)6zμ-C(R)C(NEt2)NN(CPh2)}] (5b:R=Me,6b:R=C3H5,7b:R=SiMe3,8b:R=Ph) is observed when compounds5a-5a are treated in refluxing hexane. Transformation of compoundsa tob is also obtained at room temperature within a few days. All compounds were identified by their1H NMR spectra. Compounds6a, 7a, 8a, and8b were characterized by single crystal X-ray diffraction analyses. Crystal data: for6a: space group = P21/n,a=12.853(1) A,b=24.800(7) A,c=8.947(6) A,β=99.29(3)°,Z=4, 2227 rellectionsR=0,038; for7a: space group=Pl,a=ll.483(4) A,b=14.975(4) A,c = 17.890(8) A,α = 82.80(3)°,β=94.29(7)°,γ=85.42(2),Z = 4, 5888 reflectionR = 0.035: for8a: space group = Pcab.a = 31.023(8) A.b=20.137(1) A.c=9.686(2) A.Z=8. 1651 reflections,R=0.071; for8b: space group=P21/n,a=21.459(4),b=10,100(3) A,c=28,439(8) A,ß=103.86(4)°,Z=8. 2431 reflections.R=0.057. 相似文献
13.
《Journal of molecular catalysis. A, Chemical》1998,128(1-3):201-214
The reaction of RHN(CH2)3NHR (1a,b) (a, R=2,6-iPr2C6H3; b, R=2,6-Me2C6H3) with 2 equiv of BuLi followed by 2 equiv of ClSiMe3 yields the silylated diamines R(Me3Si)N(CH2)3N(SiMe3)R (3a,b). The reaction of 3a,b with TiCl4 yields the dichloride complexes [RN(CH2)3NR]TiCl2 (4a,b) and two equiv of ClSiMe3. An X-ray study of 4a (P21/n, a=9.771(1) Å, b=14.189(1) Å, c=21.081(2) Å, β=96.27(1)°, V=2905.2(5) Å3, Z=4, T=25°C, R=0.0701, Rw=0.1495) revealed a distorted tetrahedral geometry about titanium with the aryl groups lying perpendicular to the TiN2-plane. Compounds 4a,b react with 2 equiv of MeMgBr to give the dimethyl derivatives [RN(CH2)3NR]TiMe2 (5a,b). An X-ray study of 5b (P212121, a=8.0955(10) Å, b=15.288(4) Å, c=16.909(3) Å, V=2092.8(7) Å3, Z=4, T=23°C, R=0.0759, Rw=0.1458) again revealed a distorted tetrahedral geometry about titanium with titanium–methyl bond lengths of 2.100(9) Å and 2.077(9) Å. These titanium dimethyl complexes are active catalysts for the polymerization of 1-hexene, when activated with methylaluminoxane (MAO). Activities up to 350,000 g of poly(1-hexene)/mmol catalyst·h were obtained in neat 1-hexene. These systems actively engage in chain transfer to aluminum. Equimolar amounts of 5a or 5b and B(C6F5)3 catalyze the living aspecific polymerization 1-hexene. Polydispersities (Mw/Mn) as low as 1.05 were measured. Highly active living systems are obtained when 5a is activated with {Ph3C}+[B(C6F5)4]−. A primary insertion mode (1,2 insertion) has been assigned based on both the initiation of the polymer chain and its purposeful termination with iodine. 相似文献
14.
《Tetrahedron: Asymmetry》2001,12(14):1961-1964
The absolute configurations of the palmarumycins C9 1a, C10 2, and C12 3 were assigned by comparison of the quantum-mechanically calculated with the experimental CD spectra as (2R,3S,4aS,8aR), (2R,3R,4S,4aS,8aR), and (2R,3R,4R), respectively. 相似文献
15.
《Tetrahedron: Asymmetry》1999,10(17):3319-3325
Chiral C2-symmetric diphenylphosphoramide 4 and diphenylthiophosphoramide 5 were prepared from the reaction of diphenylphosphinic chloride and diphenylthiophosphinic chloride with (1R,2R)-(−)-1,2-diaminocyclohexane in the presence of diisopropylethylamine in high yields. They were used as chiral ligands in the catalytic asymmetric addition reaction of diethylzinc to aldehydes in the presence of titanium(IV) isopropoxide to give the corresponding sec-alcohols in 70–83% ee with an (R)-configuration and in 40–50% ee with an (S)-configuration, respectively. 相似文献
16.
《Tetrahedron: Asymmetry》1999,10(15):2913-2925
A new Ti(IV) complex obtained from the C2-symmetric amino diol (1R,5R)-3-aza-3-benzyl-1,5-diphenyl pentan-1,5-diol, (1R,5R)-1, is used effectively as a Lewis acid promoter in asymmetric Diels–Alder reactions. Using various Evans' oxazolidinones as dienophiles and cyclopentadiene as the diene high yields of the adducts with moderate enantioselectivity, under different reaction conditions are achieved. The effects of solvent, temperature and ligand on the enantioselectivity of the Diels–Alder products are reported. Molecular modelling studies provide an understanding of the diastereofacial selectivity of the Diels–Alder reactions. Asymmetric carbonyl-ene reactions between various glyoxylate esters and α-methyl styrene are also described. 相似文献
17.
The synthesis of the half-sandwich compound Na[(C5H5)Ni{P(S)(CH3)2}2] is described. The anions [(C5H5)Ni{P(S)R2}2]?, 1a (R = OCH3) and 1b (R = CH3) react as bidentate sulfur ligands with [Ni2(C5H5)3]+, giving nickelocene and weakly paramagnetic dinuclear complexes of the type [(C5H5)Ni{P(S)R2}2Ni(C5H5)] (2a,b). In these compounds, the P(S)R2 units form NiPSNi bridges in such a fashion as to generate a (C5H5)NiP2 and a (C5H5)NiS2 unit. A temperature-dependent singlettriplet spin equilibrium is observed, which is essentially localized on the (C5H5)NiS2 side. Accordingly, the position of the cyclopentadienyl peak of the (C5H5)Ni unit bound to the two sulfur donor centers displays a very large temperature dependence in the 1H NMR spectra. MO model calculations (EHT) for P(S)H2?, [(C5H5)Ni{P(S)H2}2]? (1c), [(C5H5)Ni{P(S)H2}2Ni(C5H5)] (2c) and its isomer 3c allow the observed spin crossover to be explained as a consequence of the pronounced π-donor properties of the sulfur centers and allow predictions for related complexes.The green complexes 2a,b isomerize completely and irreversibly in a first-order reaction to yield the diamagnetic red compounds [{(C5H5)NiP(S)R2}2] (3a,b), in which each (C5H5)Ni unit is coordinated to one P and one S donor atom. The rate constant of isomerization of 2a, k (7.6 ± 0.3) × 10?4s?1 at 306 K, and the energy of activation, Ea 76 kJ mol?1, have been determined. The rate of isomerization is independent of the solvent, and crossover experiments verify that the isomerization is an intramolecular process without involvement of the monomeric units [(C5H5)NiP(S)R2]. 相似文献
18.
《Tetrahedron: Asymmetry》2006,17(4):674-686
New chiral NCN-pincer palladium complexes containing proline ester moieties as chiral auxiliaries have been synthesized. The parent ligands 2,6-bis{[(S)-2-(methoxycarbonyl)-1-pyrrolidinyl]methyl}-1-bromobenzene LMe and 2,6-bis{[(S)-2-(benzoxycarbonyl)-1-pyrrolidinyl]methyl}-1-bromobenzene LBn were prepared in a single synthetic step and were obtained enantiomerically pure. Neutral arylpalladium bromide complexes 1a and 1b, formed upon treatment of the respective ligands LMe and LBn with [Pd2(dba)3]·CHCl3, were isolated as mixtures of three stereoisomers (SNSNSCSC, RNSNSCSC and RNRNSCSC). The ratio of stereoisomers is approximately 1:1:0.6 in the case of methyl ester derivative 1a, whereas the bulkier benzyl ester derivative 1b predominantly forms the (SNSNSCSC)-stereoisomer. Upon abstraction of the bromide ion from unresolved mixtures of 1a and 1b, cationic complexes 2 and 3, respectively, form as single diastereoisomers in which one of the ester prolinate carbonyl groups is coordinated to palladium according to X-ray crystal structure determination. This coordination of a carbonyl group to the metal has a substantial influence on the stereochemistry and results in the formation of a single diastereoisomer, having the (RNRNSCSC)-configuration, regardless of the stereochemistry or ratio of stereoisomers of the starting bromide compound. The structures of compounds 2 and 3 were somewhat unexpected since formation of the corresponding cationic [Pd(NCN)(OH2)]+ complexes was anticipated. In preliminary tests of these cationic complexes as catalysts in the enantioselective aldol condensation of benzaldehyde with methyl isocyanoacetate, modest selectivities were observed. 相似文献
19.
First examples of tungsten aminocarbene complexes [(OC5)W{C(SiR1nR23-n)NH2}] 2a-d (R1 = Ph, R2 = Me) were synthesized via ammonolysis of the corresponding methoxycarbene complexes 1a-d. They were characterized by NMR spectroscopy, MS, IR, UV/Vis and elemental analysis, and in the case of the C-triphenylsilyl derivative 2a by single-crystal X-ray structure analysis. The reaction of P-chloro alkylidenephosphane 3 with complexes 2a-d, meant to give 2H-azaphosphirene complexes, was monitored by 31P NMR spectroscopy to reveal the formation of the products 4-7, which were presumably formed via decomposition of the transient complexes 10a-d. 相似文献
20.
Chiral C2-symmetric bis(imidazoline) pincer ligands 2a-d have been synthesized for the first time. Direct cycloplatination of these ligands with K2PtCl4 in dry acetic acid afforded the corresponding cycloplatinated pincer complexes 3a-d. The X-ray single-crystal structure of platinum complex 3d and the preliminary studies on the photoluminescent properties of 3 are reported. 相似文献