Stereocontrol in rare earth metal triflate-catalyzed 1,3-dipolar cycloaddition reaction of 2-benzopyrylium-4-olate with aldehydes

Exo-cycloadduct was obtained with high stereoselectivity by the addition of ytterbium triflate (Yb(OTf)(3)) (10 mol %) in the rhodium(II) acetate (Rh(2)(OAc)(4))-catalyzed decomposition of o-(methoxycarbonyl)-alpha-diazoacetophenone in the presence of benzaldehyde. In the reaction in the absence of Yb(OTf)(3), almost no selectivity was obtained. Stereoselectivity in the reactions with p-nitrobenzaldehyde, p-anisaldehyde, and benzyloxyacetaldehyde could be also controlled to high exo preference by the addition of Yb(OTf)(3).     

Azidolysis of alpha,beta-epoxycarboxylic acids. A water-promoted process efficiently catalyzed by indium trichloride at pH 4.0

The catalytic efficiency of InCl(3), Yb(OTf)(3), and Sc(OTf)(3) in the azidolysis of alpha,beta-epoxycarboxylic acids has been studied in water and in organic solvents, for comparison using NaN(3) and Me(3)SiN(3) as the source of the azido group. In water, the catalytic effectiveness of these metal salts strongly depends on the pH of the aqueous medium and on the type of Lewis acid catalyst. In water their catalytic activity is mostly due to the corresponding aqua ion species, the concentration of which becomes significant when the pH of the aqueous medium is below the corresponding pK(1,1) hydrolysis constant. The process is more efficient in water than in organic solvents. At pH 4.0, InCl(3) is a far better catalyst than Yb(OTf)(3) or Sc(OTf)(3) and allows the highly regio- and diasteroselective preparation of beta-azido-alpha-hydroxycarboxylic acids, which can be isolated in pure form in very high yields.     

Electrophilic chemistry of propargylic alcohols in imidazolium ionic liquids: propargylation of arenes and synthesis of propargylic ethers catalyzed by metallic triflates [Bi(OTf)3, Sc(OTf)3, Yb(OTf)3], TfOH, or B(C6F5)3

Metallic triflates M(OTf)(3) (M = Bi, Sc, Yb), immobilized in imidazolium ionic liquids [BMIM][BF(4)], [BMIM][PF(6)] and [BMIM][OTf] are efficient systems for one-pot reactions of propargylic alcohols 1,3-diphenyl-2-propyn-1-ol Ia, 1-methyl-3-phenyl-2-propyn-1-ol Ib, and 2-pentyn-1-ol Ic, with a wide range of arenes bearing activating substituents, under mild conditions. The [BMIM][PF(6)]/B(C(6)F(5))(3) and [BMIM][PF(6)]/TfOH systems were superior in propargylation with Ib and Ic, while reaction of 3-phenyl-2-propyn-1-ol Id with activated aromatics resulted in the formation of diaryl-propanones instead. Propargylation of anisole with Ib under M(OTf)(3) catalysis is highly para selective, but with TfOH or B(C(6)F(5))(3) as catalyst the ortho isomer was also formed. Steric influence of the propargylic moiety on substrate selectivity is reflected in the lack of ortho propargylation for phenol and ethylbenzene by using propargylic alcohol Ia, and notable formation of the ortho isomer employing alcohol Ib. In the later case para selectivity could be increased by running the reaction at r. t. for 10 h. The Bi(OTf)(3)-catalyzed reaction of 1,3-dimethoxybenzene with Ia led to minor formation of dipropargylated derivative, along with the monopropargyl product. Propargylation of the less reactive arenes (mesitylene, ethylbenzene, toluene), using Sc(OTf)(3) as catalyst, led increasingly to the formation of dipropargylic ethers and propargyl ketones, with no ring propargylation product with toluene. Concomitant formation of dipropargylic ether was also observed in Yb(OTf)(3)-catalyzed propargylation of β-naphthol, whereas propargylation of 2-nitro and 4-nitro-aniline led to N-propargylation. The recycling/reuse of the IL was demonstrated in representative cases with no appreciable decrease in the conversions over 3 cycles. It was also shown that recycled IL could be used to propargylate a different aromatic compound. The efficacy of IL/M(OTf)(3) and IL/TfOH systems for cross-breeding two propargylic alcohols or a propargylic alcohol with a non-propargylic alcohol and/or self-coupling, to form a wide variety of functionalized ethers is also demonstrated.     

Imino ene reaction catalyzed by ytterbium(III) triflate and TMSCl or TMSOTf

A novel combined system of Yb(OTf)(3) with TMSCl or TMSOTf catalyzed an imino ene reaction. The reaction of N-tosylbenzaldimine (1) with alpha-methylstyrene (2) proceeded smoothly to give homoallylic amine 3 in the presence of a catalytic amount of Yb(OTf)(3) and TMSCl. This catalytic system was successfully applied to the imino ene reactions of various aldimines with alkenes. This new imino ene reaction provides a unique method for the three-component coupling reaction of an aldehyde, tosylamide, and alpha-methylstyrene in the presence of Yb(OTf)(3) and TMSOTf, to give the corresponding homoallylic amine.     

Catalytic and enantioselective aza-ene and hetero-Diels-Alder reactions of alkenes and dienes with azodicarboxylates

Lewis acids such as Cu(OTf)(2), Zn(OTf)(2), Yb(OTf)(3) and Nd(OTf)(3) catalyze the aza-ene reaction of alkenes with azodicarboxylates, giving the allylic amination adducts. The use of bis(2,2,2-trichloroethyl)azodicarboxylate as the amination reagent and Cu(OTf)(2) and Yb(OTf)(3) as the catalysts gave the aza-ene reaction of different alkenes, leading to the corresponding allyl amines in high yields. Chiral copper complexes prepared from Cu(OTf)(2) and chiral bisoxazoline ligands were found to catalyze the enantioselective aza-ene reaction of azodicarboxylates with alkenes and the hetero-Diels-Alder reaction with cyclopentadiene, giving the corresponding aza-ene- and hetero-Diels-Alder adducts, respectively, in good yields and moderate enantioselectivities.     

Synthesis and characterization of Cu(2)(I,I), Cu(2)(I,II), and Cu(2)(II,II) compounds supported by two phthalazine-based ligands: influence of a hydrophobic pocket

The copper coordination chemistry of two phthalazine-based ligands of differing steric bulk was investigated. A family of dinuclear complexes were prepared from reactions of [Cu(2)(bdptz)(MeCN)(2)](OTf)(2), 1(OTf)(2), where bdptz = 1,4-bis(2,2'-dipyridylmethyl)phthalazine. Treatment of 1(OTf)(2) with NaO(2)CCH(3) afforded the class I mixed-valent compound [Cu(2)(bdptz)(2)](OTf)(3), 2(OTf)(3), by disproportionation of Cu(I). Compound 2(OTf)(3) displays an electron paramagnetic resonance spectrum, with g( parallel ) = 2.25 (A( parallel ) = 169 G) and g( perpendicular ) = 2.06, and exhibits a reversible redox wave at -452 mV versus Cp(2)Fe(+)/Cp(2)Fe. The complex [Cu(2)(bdptz)(micro-OH)(MeCN)(2)](OTf)(3), 3(OTf)(3), was prepared by chemical oxidation of 1 with AgOTf, and exposure of 1 to dioxygen afforded [Cu(2)(bdptz)(micro-OH)(2)](2)(OTs)(4), 4(OTs)(4), which can also be obtained directly from [Cu(H(2)O)(6)](OTs)(2). In compound [Cu(2)(bdptz)(micro-vpy)](OTf)(2), 5(OTf)(2), where vpy = 2-vinylpyridine, the vpy ligand bridges the two Cu(I) centers by using both its pyridine nitrogen and the olefin as donor functionalities. The sterically hindered compounds [Cu(2)(Ph(4)bdptz)(MeCN)(2)](OTf)(2), 6(OTf)(2), and [Cu(2)(Ph(4)bdptz)(micro-O(2)CCH(3))](OTf), 7(OTf), were also synthesized, where Ph(4)bdptz = 1,4-bis[bis(6-phenyl-2-pyridyl)methyl]phthalazine. Complexes 1-7 were characterized structurally by X-ray crystallography. In 6 and 7, the four phenyl rings form a hydrophobic pocket that houses the acetonitrile and acetate ligands. Complex 6 displays two reversible redox waves with E(1/2) values of +41 and +516 mV versus Cp(2)Fe(+)/Cp(2)Fe. Analysis of oxygenated solutions of 6 by electrospray ionization mass spectrometry reveals probable aromatic hydroxylation of the Ph(4)bdptz ligand. The different chemical and electrochemical behavior of 1 versus 6 highlights the influence of a hydrophobic binding pocket on the stability and reactivity of the dicopper(I) centers.     

Stereoblock copolymers and tacticity control in controlled/living radical polymerization

Three controlled/living radical polymerization processes, atom transfer radical polymerization (ATRP), reversible addition-fragmentation transfer (RAFT) polymerization, and nitroxide-mediated polymerization (NMP), were investigated for the polymerization of N,N-dimethylacrylamide in the presence of Lewis acids known to enhance isotacticity, such as yttrium trifluoromethanesulfonate (Y(OTf)(3)) and ytterbium trifluoromethanesulfonate (Yb(OTf)(3)). Poly(N,N-dimethylacrylamide) with controlled molecular weight, low polydispersity (M(w)/M(n) < 1.2), and a high proportion of meso dyads ( approximately 85%) was prepared by ATRP (with initiating system methyl 2-chloropropionate/CuCl/Me(6)TREN) and RAFT (with cumyl dithiobenzoate transfer agent) in the presence of Y(OTf)(3). The combination of NMP (using N-tert-butyl-1-diethylphosphono-2,2-dimethylpropyl nitroxide, SG1) and a Lewis acid complexation technique led to less precise control over chain architecture and microstructure ( approximately 65% meso dyads), as compared to RAFT/Y(OTf)(3) or ATRP/Y(OTf)(3). The latter two systems were used for the first one-pot synthesis of stereoblock copolymers by radical polymerization. Well-defined stereoblock copolymers, atactic-b-isotactic poly(N,N-dimethylacrylamides), were obtained by adding Y(OTf)(3) at a given time to either RAFT or ATRP polymerizations, initially started without the presence of the Lewis acid.     

Structural characterization and DFT study of V(IV)O(acac)2 in imidazolium ionic liquids

We report the structural characterization of vanadyl acetylacetonate in imidazolium room temperature ionic liquids--bbimNTf(2), bmimNTf(2), C(3)OmimNTf(2), bm(2)imNTf(2), bmimPF(6), bmimOTf, bmimBF(4), bmimMeCO(2), bmimMeSO(4), bmimMe(2)PO(4) and bmimN(CN)(2)--and organic solvents. The complex was characterized by visible electronic (Vis) and EPR spectroscopies. VO(acac)(2) shows solvatochromism in the selected ionic liquids and behaves as in organic solvents, evidencing coordination of the ionic liquid anion in the solvents with higher coordinating ability. The Lewis basicity order obtained for the IL anions was: PF(6)(-) < NTf(2)(-) < OTf(-)≈ MeCO(2)(-) < MeSO(4)(-) < BF(4)(-)≈ N(CN)(2)(-) < Me(2)PO(4)(-). The solvent effect on the spectroscopic data was tentatively examined using linear solvation energy relationships based on the Kamlet-Taft solvent scale (α, β and π*), however no suitable correlation was found with all data. The EPR characterization showed the presence of two isomers in bmimOTf, bmimMeCO(2) and bmimMe(2)PO(4), suggesting coordination of the ionic liquid anions in both equatorial and axial positions. The full geometry optimization of cis-/trans-VO(acac)(2)(OTf)(-) and cis-/trans-VO(acac)(2)(OTf)(mmim) structures was done at the B3P86/6-31G* level of theory. The calculations confirm that the anion OTf(-) is able to coordinate to VO(acac)(2) with the trans isomer being more stable than the cis by 4.8 kcal mol(-1).     

Synthesis and characterization of several dicopper(I) complexes and a spin-delocalized dicopper(I,II) mixed-valence complex using a 1,8-naphthyridine-based dinucleating ligand

The synthesis of dicopper(I) complexes [Cu2(BBAN)(MeCN)2](OTf)2 (1), [Cu2(BBAN)(py)2](OTf)2 (2), [Cu2(BBAN)(1-Me-BzIm)2](OTf)2 (3), [Cu2(BBAN)(1-Me-Im)2](OTf)2 (4), and [Cu2(BBAN)(mu-O2CCPh3)](OTf) (5), where BBAN = 2,7-bis((dibenzylamino)methyl)-1,8-naphthyridine, py = pyridine, 1-Me-Im = 1-methylimidazole, and 1-Me-BzIm = 1-methylbenzimidazole, are described. Short copper-copper distances ranging from 2.6151(6) to 2.7325(5) A were observed in the solid-state structures of these complexes depending on the terminal ligands used. The cyclic voltammogram of compound 5 dissolved in THF exhibited a reversible redox wave at E1/2 = -25 mV vs Cp2Fe+/Cp2Fe. When complex 5 was treated with 1 equiv of silver(I) triflate, a mixed-valence dicopper(I,II) complex [Cu2(BBAN)(mu-O2CCPh3)(OTf)](OTf) (6) was prepared. A short copper-copper distance of 2.4493(14) A observed from the solid-state structure indicates the presence of a copper-copper interaction. Variable-temperature EPR studies showed that complex 6 has a fully delocalized electronic structure in frozen 2-methyltetrahydrofuran solution down to liquid helium temperature. The presence of anionic ligands seems to be an important factor to stabilize the mixed-valence dicopper(I,II) state. Compounds 1-4 with neutral nitrogen-donor terminal ligands cannot be oxidized to the mixed-valence analogues either chemically or electrochemically.     

A survey of acid catalysis and oxidation conditions in the two-step, one-flask synthesis of meso-substituted corroles via dipyrromethanedicarbinols and pyrrole

The reaction of dipyrromethanedicarbinols with pyrrole leading to meso-substituted corroles was investigated to determine whether mild acid catalysts [Dy(OTf)(3), Yb(OTf)(3), Sc(OTf)(3), and InCl(3)] known to provide porphyrins from dipyrromethanecarbinol species while suppressing undesired reversibility (resulting in scrambling) are applicable to reactions affording corrole, and to explore the requirements of the oxidation step. We examined a model reaction leading to meso-triphenylcorrole (TPC) to survey the effect of acid catalyst, acid concentration, ratio of pyrrole to dipyrromethanedicarbinol, oxidant, oxidant quantity, and reaction time on the yield of TPC (by UV-vis) in reactions performed at room temperature in CH(2)Cl(2). Key to this survey was a modification of the well-known spectrophotometric method for monitoring reactions leading to porphyrin. The survey revealed that TPC could be prepared via a subset of the mild acid catalysts [Dy(OTf)(3) and Yb(OTf)(3)], and a preparative-scale reaction afforded an isolated yield of TPC of 49%, devoid of porphyrin. Suppression of reversible processes was further demonstrated by the synthesis of three corroles bearing different meso substituents in defined locations in isolated yields ranging from 50% to 80%. The reaction conditions were applicable to a dipyrromethanedicarbinol bearing electron-withdrawing pentafluorophenyl substituents-provided that the reaction time of the condensation step was increased. We identified circumstances under which DDQ can cause severe interference with the detection and isolation of some corroles, we found that the yield and purity of the corrole depend on judicious selection of oxidation conditions, and we assessed the sensitivity toward light of dilute solutions of the corroles prepared in this study.     

Secondary benzylation using benzyl alcohols catalyzed by lanthanoid, scandium, and hafnium triflate

The combination of a secondary benzyl alcohol and a metal triflate (e.g., La, Yb, Sc, and Hf triflate) in nitromethane was a highly effective secondary-benzylation system. Secondary benzylation of carbon (aromatic compounds, olefins, an enol acetate), nitrogen (amide derivatives), and oxygen (alcohols) nucleophiles was carried out with a secondary benzyl alcohol and 0.01-1 mol % of a metal triflate in the presence of water. Secondary benzyl alcohols and nucleophiles bearing acid-sensitive functional groups (e.g., tert-butyldimethylsilyloxy and acetoxy groups and methyl and benzyl esters) could be used for alkylation. Hf(OTf)4 was the most active catalyst for this alkylation, and trifluoromethanesulfonic acid (triflic acid, TfOH) was also a good catalyst. The catalytic activity of metal triflates and TfOH increased in the order La(OTf)3 < Yb(OTf)3 < TfOH < Sc(OTf)3 < Hf(OTf)4. A mechanistic study was also performed. The reaction of 1-phenylethanol (4a) in the presence of Sc(OTf)3 in nitromethane gave an equilibrium mixture of 4a and bis(1-phenylethyl) ether (54). Addition of a carbon nucleophile to the equilibrium mixture gave alkylated product in high yield.     

Constructing homo- and hetero-metallic molecular topologies using pyridylcarboxylates as spacers: preparation of a half-ring complex with active coordination sites

Addition of isonicotinic acid NC(5)H(4)CO(2)H (or isonicH) to [Pt(dppf)(MeCN)(2)](2+)2OTf(-)(dppf = 1,1'-bis(diphenylphosphino)ferrocene, OTf = triflate) affords a mixture of the homometallic molecular square [Pt(4)(dppf)(4)(mu-O(2)CC(5)H(4)N)(4)](4+)4OTf(-), 1 and its precursor intermediate [Pt(dppf)(eta(1)-NC(5)H(4)CO(2)H)(2)](2+)2OTf(-), 2. The latter captures [Pd(dppf)(MeCN)(2)](2+)2OTf(-) to give a heterometallic square, [Pt(2)Pd(2)(dppf)(4)(mu-O(2)CC(5)H(4)N)(4)](4+)4OTf(-), 3. Slight skeletal modification of the ligand leads to different assemblies. This is illustrated by the addition of NC(5)H(4)CH(2)CO(2)H.HCl to [Pt(dppf)(MeCN)(2)](2+)2OTf(-) to give [PtCl(dppf)(NC(5)H(4)CH(2)CO(2)H)](+)OTf(-), 4, which reacts with another equivalent of AgOTf to yield the dibridged complex [Pt(2)(dppf)(2)(mu-NC(5)H(4)CH(2)CO(2))(2)](2+)2OTf(-), 5. All complexes, with the exception of , have been structurally characterized by single-crystal X-ray crystallography. Complexes 2 and 4 are potential precursors to further molecular topologies.     

Metal-to-ligand charge-transfer sensitisation of near-infrared emitting lanthanides in trimetallic arrays M2Ln (M=Ru, Re or Os; Ln=Nd, Er or Yb)

The new pro-ligand 4-methyl-4'-(carbonylamino(2-(tert-butoxycarbonylamino)ethyl))-2,2'-bipyridyl (L1) has been prepared and used to synthesise the complex fac-Re(I)Cl(CO)3(L1) 1 and the complex salts [M(II)(bipy)2(L1)](PF6)2 (M=RuII 8 or OsII 15). Deprotection with trifluoroacetic acid affords the amine-functionalised derivatives fac-Re(I)Cl(CO)3(L2) 2, [M(II)(bipy)2(L2)](PF6)2 (M=RuII 9 or OsII 16) which react with the dianhydride of diethylenetriamine pentaacetic acid (DTPA) to give the binuclear complex {fac-Re(I)Cl(CO)3}2(L3) 3 and the complex salts [{M(II)(bipy)2}2(L3)](PF6)4 (M = RuII 10 or OsII 17). The latter react with salts Ln(OTf)3 to afford a series of 12 heterotrimetallic compounds that contain a lanthanide (Ln) ion in the DTPA binding site; {fac-Re(I)Cl(CO)3}2(L3)LnIII (Ln=Nd 4, Er 5, Yb 6 or Y 7) and [{M(II)(bipy)2}2(L3)LnIII](PF6)(OTf)3 (M=RuII, Ln=Nd 11, Er 12, Yb 13 or Y 14; M=OsII, Ln=Nd 18, Er 19, Yb 20 or Y 21). All of these trimetallic species display absorption bands ascribed to metal-to-ligand charge-transfer (MLCT) excitations, and luminescence measurements show that these excited states can be used to sensitise near-infrared emission from LnIII (Ln=Nd, Er or Yb) ions. Single crystal X-ray structures of L1 and [RuII(bipy)2(L2H)](H2PO4)3.(CH3)2CO.0.8H2O were obtained, the latter revealing the presence of H2PO4- counter anions, the source of which is presumed to be hydrolysis of PF6- ions.     

Self-assembly and molecular recognition of a luminescent gold rectangle

A luminescent molecular rectangle [Au(4)(micro-PAnP)(2)(micro-bipy)(2)](OTf)(4) (1.(OTf)(4)) (PAnP = 9,10-bis(diphenylphosphino)anthracene, bipy = 4,4'-bipyridine, X = NO(3)(-) or OTf(-)), synthesized from the self-assembly of the molecular "clip" Au(2)(micro-PAnP)(OTf)(2) and bipy, shows a large rectangular cavity of 7.921(3) x 16.76(3) A. The electronic absorption and emission spectroscopy, and electrochemistry of the metallacyclophane, have been studied. The 1(4+) ions are self-assembled into 2D mosaic in the solid state via complementary edge-to-face interactions between the Ph groups. (1)H NMR titrations ratify the 1:1 complexation between 1(4+) and various aromatic molecules. Comparing the structures of the inclusion complexes indicates an induced-fit mechanism operating in the binding. The emission of 1(4+) is quenched upon the guest binding. The binding constants are determined by both (1)H NMR and fluorescence titrations. Solvophobic and ion-dipole effects are shown to be important in stabilizing the inclusion complexes.     

三氟甲烷磺酸稀土盐对聚丙烯热稳定性的影响及机理

通过熔融共混将三氟甲烷磺酸镱[Yb(OTf)₃]和三氟甲烷磺酸镧[La(OTf)₃]添加至聚丙烯(PP)中, 制得PP/Yb和PP/La材料, 并对其热稳定性进行表征. 热失重分析(TGA)和差示扫描量热分析(DSC)结果显示, Yb(OTf)₃和La(OTf)₃均可以显著提高聚丙烯的热稳定性. 当Yb(OTf)₃添加量仅为1%(质量分数)时, PP的起始分解温度从275 ℃提高至305 ℃, 最大分解温度从384 ℃提高至405 ℃, 160 ℃下的氧化诱导时间从12.1 min延长至43.0 min, 热焓从1907 J/g降低至483 J/g; 而PP/La1的起始分解温度、 最大分解温度、 160 ℃下的氧化诱导时间和热焓分别为300 ℃, 409 ℃, 18.6 min和633 J/g. 结果表明, La(OTf)₃对聚丙烯热稳定性的改善作用弱于Yb(OTf)₃, 对2种稀土盐产生不同实验结果的原因进行分析并提出机制. 由于阴离子和阳离子的共同作用, Yb(OTf)₃和La(OTf)₃均可提高PP的热氧稳定性. La(OTf)₃中三氟甲烷磺酸根的自由基捕捉能力和稀土离子的配位能力发挥主要作用, 而Yb(OTf)₃中的稀土离子的高反应活性也起到关键作用.     

Electrochemistry of nanocrystalline 3C silicon carbide films

Silicon carbide (SiC) films have been used frequently for high-frequency and powder devices but have seldom been applied as the electrode material. In this paper, we have investigated the electrochemical properties of the nanocrystalline 3C-SiC film in detail. A film with grain sizes of 5 to 20 nm shows a surface roughness of about 30 nm. The resistivity of the film is in the range of 3.5-6.2 kΩ cm. In 0.1 M H(2)SO(4) solution, the film has a double-layer capacitance of 30-35 μF cm(-2) and a potential window of 3.0 V if an absolute current density of 0.1 mA cm(-2) is defined as the threshold. Its electrochemical activity was examined by using redox probes of [Ru(NH(3))(6)](2+/3+) and [Fe(CN)(6)](3-/4-) in aqueous solutions and by using redox probes of quinone and ferrocene in nonaqueous solutions. Diffusion-controlled, quasi-reversible electrode processes were achieved in four cases. The surface chemistry of the nanocrystalline 3C-SiC film was studied by electrochemical grafting with 4-nitrobenzenediazonium salts. The grafting was confirmed by time-of-flight secondary ion mass spectroscopy. All these results confirm that the nanocrystalline 3C-SiC film is promising for use as an electrode material.     

Lanthanide triflate-catalyzed arene acylation. Relation to classical Friedel-Crafts acylation

Lanthanide trifluoromethanesulfonates, Ln(OTf) 3 (OTf (-) = trifluoromethanesulfonate), serve as effective precatalysts for the rapid, regioselective, intermolecular acylation of activated arenes. This contribution probes mechanism and metal ionic radius effects in the catalytic lanthanide triflate-mediated acylation of anisole with acetic anhydride. Kinetic studies of Ln(OTf) 3 (Ln = La, Eu, Yb, Lu)-mediated anisole acylation with acetic anhydride in nitromethane reveal the rate law nu approximately k 3 [Ln (3+)] (1)[acetic anhydride] (1)[anisole] (1). Eyring and Arrhenius analyses yield Delta H++ = 12.9 (4) kcal.mol (-1), Delta S++ = -44.8 (1.3) e.u., and E a = 13.1 (4) kcal.mol (-1) for Ln = Yb, with the negative Delta S++ implying a highly organized transition state. The observed primary kinetic isotope effect of k H/ k D = 2.6 +/- 0.15 is consistent with arene C-H bond scission in the turnover-limiting step. The proposed catalytic pathway involves precatalyst formation via interaction of Ln(OTf) 3 with acetic anhydride, followed by Ln (3+)-anisole pi-complexation, substrate-electrophile sigma-complex formation, and turnover-limiting C-H bond scission. Lanthanide size effects on turnover frequencies are consistent with a transition state lacking significant ionic radius-dependent steric constraints. Substrate-Ln (3+) interactions using paramagnetic Gd (3+) and Yb (3+) NMR probes and factors affecting reaction rates such as arene substituent and added LiClO 4 cocatalyst are also explored.     

Versatile use of ytterbium(III) triflate and acid washed molecular sieves in the activation of glycosyl trifluoroacetimidate donors. Assemblage of a biologically relevant tetrasaccharide sequence of Globo H

The nonreducing tetrasaccharide terminus of Globo H has been assembled in good yield and excellent stereocontrol exclusively by using mild and moisture stable agents such as Yb(OTf)(3) and acid washed molecular sieves for the activation of glycosyltrifluoroacetimidate donors in the glycosylation steps.     

Mononuclear and dinuclear complexes with a [Ru(tBu2PCH2CH2PtBu2)(CO)] core

Thermolysis of solid [Ru(d(t)bpe)(CO)2Cl2](2, d(t)bpe =(t)Bu2PCH2CH2P(t)Bu2) under vacuum affords the five-coordinate complex [Ru(d(t)bpe)(CO)Cl2] (4), which was shown by X-ray crystallography to contain a weak remote agostic interaction. In solution, 4 can be readily trapped by CO, CH3CN or water to give [Ru(d(t)bpe)(CO)(L)Cl2](L = CO, 2; L = CH3CN, 6; L = H2O, 7). Reaction of 4 with AgOTf/H2O yields the tris-aqua complex [Ru(d(t)bpe)(CO)(H2O)3](OTf)2 (8), which has been structurally characterised and probed in solution by pulsed-gradient spin echo (PGSE) NMR spectroscopy. The water ligands in 8 are labile and easily substituted to give [Ru(d(t)bpe)(CO)(NCCH3)3](OTf)2 (10) and [Ru(d(t)bpe)(CO)(DMSO)3](OTf)2 (11). In the presence of CO, the tris-aqua complex undergoes water-gas shift chemistry with formation of the cationic hydride species [Ru(d(t)bpe)(CO)3H](OTf) (12) and CO2. X-Ray crystal structures of complexes 2, 4, 6, 8 and 11-12 are reported along with those for [{Ru(d(t)bpe)(CO)}2(mu-Cl)2(mu-OTf)](OTf) (3), [{Ru(d(t)bpe)(CO)}2(mu-Cl)3][Ru(d(t)bpe)(CO)Cl3](5) and [Ru(d(t)bpe)(CO)(H2O)2(OTf)](OTf)(9).     

(NH_4)_(42)[Mo_(132)O_(372)(CH_3COO)_(30)(H_2O)_(72)]膜修饰电极的构筑和电化学性质的研究

由于过渡金属替代的多金属氧酸盐(polyoxometalates)的催化、磁性、电化学等性质,越来越受到人们的关注~([1-7]). 目前世界上约有10亿人生活在缺碘地区,碘的缺乏严重影响人类健康.对食物、生物临床、环境及工业中碘含量检测很有实际意义.