From tetragermacyclobutene to tetragermacyclobutadiene dianion to tetragermacyclobutadiene transition metal complexes

The reaction of 3,4-dichlorotetragermetene derivative 2 with Na(2)[Fe(CO)(4)] in THF produced a (tetragermacyclobutadiene)tricarbonyliron complex, [{η(4)-((t)Bu(2)MeSi)(4)Ge(4)}]Fe(CO)(3)4, which has a slightly folded Ge(4) ring perhaptocoordinated to the Fe center. Structural and spectral characteristics of 4 show a remarkable π-donating ability of the tetragermacyclobutadiene ligand toward the transition metal, surpassing that of tetrasilacyclobutadiene and cyclobutadiene ligands. Reduction of 2 with KC(8) resulted in exclusive formation of the dipotassium salt of the tetragermacyclobutadiene dianion derivative 3(2-)·[K(+)(thf)(2)](2), representing a rare example of a 6π-electron compound that, on the basis of its structural and magnetic properties, was recognized as a nonaromatic species. Reaction of 3(2-)·[K(+)(thf)(2)](2) with CpCoI(2)(PPh(3)) produced a (cyclopentadienyl)(tetragermacyclobutadiene)cobalt complex, [{η(4)-((t)Bu(2)MeSi)(4)Ge(4)}]CoCp 7, as the first example of a sandwich compound featuring an all-germanium-containing cyclic polyene ligand.     

A new efficient route to 3-vinylthiophene

The synthesis of 3-vinylthiophene was efficiently achieved in two steps. 3-(2-bromoethyl)thiophene prepared from 3-(2-ethanol)thiophene was converted to the title compound (70% overall yield) using tetraglyme as a solvent and 1,8-diazabicyclo[5.4.0]undec-7-ene as a base.     

Corrections to scaling and crossover from good- to theta-solvent regimes of interacting polymers

We exploit known properties of universal ratios, involving the radius of gyration R(g), the second and third virial coefficients B(2) and B(3), and the effective pair potential between the centers of mass of self-avoiding polymer chains with nearest-neighbor attraction, as well as Monte Carlo simulations, to investigate the crossover from good- to theta-solvent regimes of polymers of finite length L. The scaling limit and finite-L corrections to scaling are investigated in the good-solvent case and close to the theta temperature. Detailed interpolation formulas are derived from Monte Carlo data and results for the Edwards two-parameter model, providing estimates of universal ratios as functions of the observable ratio A(2)=B(2)/R(g) (3) over the whole temperature range, from the theta point to the good-solvent regime. The convergence with L (L< or =8000) is found to be satisfactory under good-solvent conditions, but longer chains would be required to match theoretical predictions near the theta point, due to logarithmic corrections. A quantitative estimate of the universal ratio A(3)=B(3)/R(g) (6) as a function of temperature shows that the third virial coefficient remains positive throughout, and goes through a pronounced minimum at the theta temperature, which goes to zero as 1/ln L in the scaling limit.     

Dissociative electron attachment to triflates

Gas phase studies of dissociative electron attachment to simple alkyl (CF(3)SO(3)CH(3)) and aryl (C(6)H(5)SO(3)CF(3) and CF(3)SO(3)C(6)H(4)CH(3)) triflates, model molecules of nonionic photoacid generators for modern lithographic applications, were performed. The fragmentation pathways under electron impact below 10 eV were identified by means of crossed electron-molecular beam mass spectrometry. Major dissociation channels involved C-O, S-O, or C-S bond scissions in the triflate moiety leading to the formation of triflate (OTf(-)), triflyl (Tf(-)), or sulfonate (RSO(3)(-)) anions, respectively. A resonance leading to C-O bond breakage and OTf(-) formation in alkyl triflates occurred at electron energies about 0.5 eV lower than the corresponding resonance in aryl triflates. A resonance leading to S-O bond breakage and Tf(-) formation in aryl triflates occurred surprisingly at the same electron energies as C-O bond breakage. In case of alkyl triflates S-O bond breakage required 1.4 eV higher electron energies to occur and proceeded with substantially lower yields than in aryl triflates. C-S bond scission occurred for all presently studied triflates at energies close to 3 eV.     

Oxidative addition of C-H bonds to RhCl(PMe3)3: relevant to the catalytic transformation of hydrocarbons

RhCl(PMe3)3 (1) reacts with benzene under irradiation to give the oxidative addition product, Rh(C6H5)(H)Cl(PMe3)3 (2). The reaction is promoted under CO2 atmosphere. The structure of 2 was fully characterized by X-ray crystallography as well as NMR, IR, and elemental analysis. The adduct (2) is unstable in solution even at room temperature to regenerate benzene and 1. The thermolysis of 2 under a CO atmosphere produces benzaldehyde along with the reductive elimination product, benzene. On the other hand, the prolonged photoreaction of 1 with benzene under CO2 resulted in the activation of the C-H bond and CO2 to yield Rh(C6H5)(eta2-CO3)(PMe3)3 (3).     

A paradigmatic change: linking fullerenes to electron acceptors

The potential of Lu(3)N@C(80) and its analogues as electron acceptors in the areas of photovoltaics and artificial photosynthesis is tremendous. To this date, their electron-donating properties have never been explored, despite the facile oxidations that they reveal when compared to those of C(60). Herein, we report on the synthesis and physicochemical studies of a covalently linked Lu(3)N@C(80)-perylenebisimide (PDI) conjugate, in which PDI acts as the light harvester and the electron acceptor. Most important is the unambiguous evidence--in terms of spectroscopy and kinetics--that corroborates a photoinduced electron transfer evolving from the ground state of Lu(3)N@C(80) to the singlet excited state of PDI. In stark contrast, the photoreactivity of a C(60)-PDI conjugate is exclusively governed by a cascade of energy-transfer processes. Also, the electron-donating property of the Lu(3)N@C(80) moiety was confirmed through constructing and testing a bilayer heterojunction solar cell device with a PDI and Lu(3)N@C(80) derivative as electron acceptor and electron donor, respectively. In particular, a positive photovoltage of 0.46 V and a negative short circuit current density of 0.38 mA are observed with PDI/Ca as anode and ITO/Lu(3)N@C(80) as cathode. Although the devices were not optimized, the sign of the V(OC) and the flow direction of J(SC) clearly underline the unique oxidative role of Lu(3)N@C(80) within electron donor-acceptor conjugates toward the construction of novel optoelectronic devices.     

Diastereoselective self-assembly of chiral diamine-chelated aryllithiums to dimeric aggregates

Aryllithium compounds [LiC6H4(CH2N(Et)CH2CH2NEt2)-2]2 (2b), [LiC6H4(CH(Me)N(Me)CH2CH2NMe2-(R))-2]2 ((R)-3b), and [LiC6H4(CH(Me)N(Me)CH2CH2NMe2-(rac))-2]2 ((rac)-3b) were synthesized and characterized in the solid state and in solution. X-ray crystallographic studies of 2b and (R)-3b and molecular weight determinations of 2b, (R)-3b, and (rac)-3b by cryoscopy in benzene showed that, both in the solid state and in apolar, noncoordinating solvents such as benzene, these compounds exist as discrete dimeric aggregates. For (R)-3b and (rac)-3b the aggregation process of two monomeric aryllithium units to one dimer is highly diastereoselective.     

Tandem electrostatic effect from the first to the third aglycon in the trimeric RNA owing to the nearest-neighbor interaction

We here show an electrostatic polar-pi interaction from the first to the third aglycon, via the second aglycon, in the ground state in two single stranded trimeric RNAs, 5'-GpA(1)pA(2)-3' (3) and 5'-GpApC-3' (4), as a result of intramolecular nearest neighbor offset-stacking. The experimental evidence in support of this conclusion has been obtained by comparing the pK(a)s of each aglycone in the two trimers with those of guanosine 3'-ethyl phosphate, GpEt (1) and 5'-GpA-3' (2): Thus, the pK(a) of N(1)-H of guanin-9-yl of 5'-GpA(1)pA(2)-3' (3) could be measured by pH titration (pH 7.3-11.6) of its own deltaH8G (pK(a) 9.75 +/- 0.02) as well as from deltaH8A(1) (pK(a) 9.72 +/- 0.02) and deltaH2A(1) (pK(a) 9.83 +/- 0.04) of the neighboring pA(1)p moiety and the deltaH8A(2) (pK(a) 9.83 +/- 0.02) of the terminal pA(2) moiety. Similarly, the pH titration of GpApC (4) shows the pK(a) of N(1)-H of guanin-9-yl from its own deltaH8G (pK(a) 9.88 +/- 0.03) as well as from deltaH8A (pK(a) 9.87 +/- 0.01) of the neighboring pAp moiety, and deltaH5/H6C (pK(a) 9.88 +/- 0.01 and 9.90 +/- 0.01 respectively) of the 3'-terminal cytosin-1-yl. This intramolecular nearest neighbor electrostatic interaction in the single-stranded RNA modulates the pseudoaromaticity of the nearest neighbors by almost total transmission of because they constitute an extended array of offset-stacked coupled aromatic heterocycles within a polyanionic sugar-phosphate backbone at the ground state. The enhanced basicity of Gp residue by ca. 0.6 pK(a) unit in the trimers compared to that of the dimer is a result of the change in the electrostatic microenvironment owing to the nearest neighbors in the former (the nucleobases as well as the phosphates). Thus, the from the 5'-guanylate ion to the 3'-end aglycon via the central adenin-9-yl is 55 to 56 kJ mol(-)(1) in each step through a distance spanning approximately 6.8 A in an unfolded state. As a result, the pK(a) of guanin-9-yl moiety has become 9.25 +/- 0.02 in GpEt (1), 9.17 +/- 0.02 in GpA (2), 9.75 +/- 0.02 in GpApA (3), and 9.88 +/- 0.03 in GpApC (4). This means that guanin-9-yl moiety of trimers 3 and 4 is more basic than in the monomer or the dimer. The net outcome of this electrostatic cross-talk between the two neighboring heterocycles is creation of new hybrid aglycones in an oligo or polynucleotide, whose physicochemical property and the pseudoaromatic character are completely dependent both upon the nearest neighbors, and whether they are stacked or unstacked. Thus, this tunable physicochemical property of an aglycon (an array of the extended genetic code) may have considerable implication in our understanding of the specific ligand binding ability of an aptamer, the pK(a) and the hydrogen bonding ability of nucleic acids in a microenvironment, or in the triplet usage by the anticodon-codon interaction in the protein biosynthesis in the ribosome.     

Density functional calculations on the conversion of azide and carbon monoxide to isocyanate and dinitrogen by a nickel to sulfur rebound mechanism

Density functional calculations (B3 LYP & BP86) on a model system for the reaction between carbon monoxide and [Ni(N(3))('S(3)')](-) ('S(3)'(2-)=bis(2-mercaptophenyl)sulfide (2-)) predict a three-step mechanism. First, CO attacks the nickel to generate a pseudo "square-pyramidal" complex, in which CO, N(3) (-), and two sulfides are basal and the central S atom of the 'S(3)'(2-) ligand backs away from Ni to form a weak Ni-S apical bond. Then, CO inserts into the Ni-N bond and the weak apical Ni--S bond rebounds to its original strength as the nickel forms a square-planar intermediate. Finally, in a one-step process N(2) leaves as the remaining N atom and carbonyl rearrange to produce the nickel isocyanate product [Ni(NCO)('S(3)')](-).     

Studies relevant to catalytic reduction of dinitrogen to ammonia by molybdenum triamidoamine complexes

In this paper we explore several issues surrounding the catalytic reduction of dinitrogen by molybdenum compounds that contain the [(HIPTNCH2CH2)3N]3- ligand (where HIPT = 3,5-(2,4,6-i-Pr3C6H2)2C6H3). Four additional plausible intermediates in the catalytic dinitrogen reduction have now been crystallographically characterized; they are MoN= NH (Mo = [(HIPTNCH2CH2)3N]Mo), [Mo=NNH2][BAr'4] (Ar' = 3,5-(CF3)2C6H3), [Mo=NH][BAr'4], and Mo(NH3). We also have crystallographically characterized a 2,6-lutidine complex, Mo(2,6-Lut)+, which is formed upon treatment of MoH with [2,6-LutH][B(C6F5)4]. We focus on the synthesis of compounds that have not yet been isolated, which include Mo=NNH2, Mo=NH, and Mo(NH2). Mo=NNH2, formed by reduction of [Mo=NNH2]+, has not been observed. It decomposes to give mixtures that contain two or more of the following: MoN=NH, Mo triple bond N, Mo(NH3)+, Mo(NH3), and ammonia. Mo=NH, which can be prepared by reduction of [Mo=NH]+, is stable for long periods in the presence of a small amount of CrCp*2, but in the absence of CrCp*2, and in the presence of Mo=NH+ as a catalyst, Mo=NH is slowly converted into a mixture of Mo triple bond N and Mo(NH2). Mo(NH2) can be produced independently by deprotonation of Mo(NH3)+ with LiN(SiMe3)2 in THF, but it decomposes to Mo triple bond N upon attempted isolation. Although catalytic reduction of dinitrogen could involve up to 14 intermediates in a "linear" sequence that involves addition of "external" protons and/or electrons, it seems likely now that several of these intermediates, along with ammonia and/or dihydrogen, can be produced in several reactions between intermediates that themselves behave as proton and/or electron sources.     

接触不同浓度铅工人的职业危害调查研究

探讨了空气中不同浓度铅对作业工人健康的影响。选择本地区不同铅浓度的两个厂矿的１７７名接触铅工厂为调查对象,并以不接触铅而其它条件相同的行政人员为对照组。对接触不同浓度铅和对照组的人员作全面休查体并结合实验室作有关生物指标检测。结果表明,接触较高铅浓度的某蓄电池厂９８名工厂,受铅职业危害较严重,检出慢性铅中毒１４人（占１４．２％）,铅吸收１０人（占１０．２％）,且发生症状和体征之阳性率亦比铅锌矿和对     

Easy hydrolysis of white phosphorus coordinated to ruthenium

The P4 molecule bound to ruthenium as an eta1-ligand in [CpRu(PPh3)2(eta1-P4)]Y (Y = PF6, CF3SO3) undergoes an easy reaction with water in exceedingly mild conditions to yield PH3, which remains coordinated to the [CpRu(PPh3)2] fragment, and oxygenated derivatives.     

Nitrogen fixation to cyanide at a molybdenum center

Facile methoxymethylation of N(2)-derived nitride NMo(N[(t)Bu]Ar)(3) provided the imido cation [MeOCH(2)NMo(N[(t)Bu]Ar)(3)](+) as its triflate salt in 88% yield. Treatment of the latter with LiN(SiMe(3))(2) provided blue methoxyketimide complex MeO(H)CNMo(N[(t)Bu]Ar)(3) in 95% yield. Conversion of the latter to the terminal cyanide complex NCMo(N[(t)Bu]Ar)(3), which was the subject of a single-crystal X-ray diffraction study, was accomplished in 51% yield upon treatment with a combination of SnCl(2) and Me(2)NSiMe(3).     

Highly efficient ruthenium-catalyzed oxime to amide rearrangement

A wide range of aldoximes has been converted into the corresponding amides using the ruthenium-based catalyst Ru(PPh3)3(CO)H2/dppe/TsOH. The amides are generated in high yield and selectivity, with catalyst loading as low as 0.04 mol %.     

An efficient iridium catalyst for reduction of carbon dioxide to methane with trialkylsilanes

Cationic silane complexes of general structure (POCOP)Ir(H)(HSiR(3)) {POCOP = 2,6-[OP(tBu)(2)](2)C(6)H(3)} catalyze hydrosilylations of CO(2). Using bulky silanes results in formation of bis(silyl)acetals and methyl silyl ethers as well as siloxanes and CH(4). Using less bulky silanes such as Me(2)EtSiH or Me(2)PhSiH results in rapid formation of CH(4) and siloxane with no detection of bis(silyl)acetal and methyl silyl ether intermediates. The catalyst system is long-lived, and 8300 turnovers can be achieved using Me(2)PhSiH with a 0.0077 mol % loading of iridium. The proposed mechanism for the conversion of CO(2) to CH(4) involves initial formation of the unobserved HCOOSiR(3). This formate ester is then reduced sequentially to R(3)SiOCH(2)OSiR(3), then R(3)SiOCH(3), and finally to R(3)SiOSiR(3) and CH(4).     

Thermodynamic, kinetic, and mechanistic study of oxygen atom transfer from mesityl nitrile oxide to phosphines and to a terminal metal phosphido complex

The enthalpies of oxygen atom transfer (OAT) from mesityl nitrile oxide (MesCNO) to Me(3)P, Cy(3)P, Ph(3)P, and the complex (Ar[(t)Bu]N)(3)MoP (Ar = 3,5-C(6)H(3)Me(2)) have been measured by solution calorimetry yielding the following P-O bond dissociation enthalpy estimates in toluene solution (±3 kcal mol(-1)): Me(3)PO [138.5], Cy(3)PO [137.6], Ph(3)PO [132.2], (Ar[(t)Bu]N)(3)MoPO [108.9]. The data for (Ar[(t)Bu]N)(3)MoPO yield an estimate of 60.2 kcal mol(-1) for dissociation of PO from (Ar[(t)Bu]N)(3)MoPO. The mechanism of OAT from MesCNO to R(3)P and (Ar[(t)Bu]N)(3)MoP has been investigated by UV-vis and FTIR kinetic studies as well as computationally. Reactivity of R(3)P and (Ar[(t)Bu]N)(3)MoP with MesCNO is proposed to occur by nucleophilic attack by the lone pair of electrons on the phosphine or phosphide to the electrophilic C atom of MesCNO forming an adduct rather than direct attack at the terminal O. This mechanism is supported by computational studies. In addition, reaction of the N-heterocyclic carbene SIPr (SIPr = 1,3-bis(diisopropyl)phenylimidazolin-2-ylidene) with MesCNO results in formation of a stable adduct in which the lone pair of the carbene attacks the C atom of MesCNO. The crystal structure of the blue SIPr·MesCNO adduct is reported, and resembles one of the computed structures for attack of the lone pair of electrons of Me(3)P on the C atom of MesCNO. Furthermore, this adduct in which the electrophilic C atom of MesCNO is blocked by coordination to the NHC does not undergo OAT with R(3)P. However, it does undergo rapid OAT with coordinatively unsaturated metal complexes such as (Ar[(t)Bu]N)(3)V since these proceed by attack of the unblocked terminal O site of the SIPr·MesCNO adduct rather than at the blocked C site. OAT from MesCNO to pyridine, tetrahydrothiophene, and (Ar[(t)Bu]N)(3)MoN was found not to proceed in spite of thermochemical favorability.     

Oxygen binding to sulfur in nitrosylated iron--thiolate complexes: relevance to the Fe-containing nitrile hydratases

Iron-nitrosyl complex containing S-bonded monosulfinate [PPN][(NO)Fe(S,SO2-C6H4)(S,S-C6H4)] (3) has been isolated from sulfur oxygenation of complex [PPN][(NO)Fe(S,S-C6H4)2] (2) which is obtained from addition of NO molecule to [PPN][(C4H8O)Fe(S,S-C6H4)2] (1) in organic solvents. This result reveals that binding of NO to the iron center promotes sulfur oxygenation of iron dithiolates by dioxygen and stabilizes the S-bonded sulfinate iron species. Analysis of the bond angles for complexes 2 and 3 reveals that iron is best described as existing in a distorted trigonal bipyramidal coordination environment surrounded by one NO, three thiolates, and one sulfinate in complex 3, whereas the distorted square pyramidal geometry is adopted in complex 2. Complex 3 further reacts in organic solvents with molecular oxygen in the presence of [PPN][NO2] to produce the dinuclear bis(sulfinate) complex [PPN]2[(NO)Fe(SO2,SO2-C6H4)(S,S-C6H4)]2 (4). Complex 3 showed reaction with PPh3 in THF/CH2Cl2 to yield complex 2 and Ph3PO. Upon photolysis of CH2Cl2 solution of complex 3 under N2 purge at ambient temperature, the UV-vis and IR spectra consistent with the formation of complex 2 demonstrate that complex 2 and 3 are photochemically interconvertible. Obviously, complex 3 is thermally quite stable but is photochemically active toward [O] release. Also described are the X-ray crystal structures of 3 and 4.     

An efficient approach to derive hydroxyl groups on the surface of barium titanate nanoparticles to improve its chemical modification ability

Highly hydroxylated barium titanate (BaTiO(3)) nanoparticles have been prepared via an easy and gentle approach which oxidizes BaTiO(3) nanoparticles using an aqueous solution of hydrogen peroxide (H(2)O(2)). The hydroxylated BaTiO(3) surface reacts with sodium oleate (SOA) to form oleophilic layers that greatly enhance the dispersion of BaTiO(3) nanoparticles in organic solvents such as tetrahydrofuran, toluene, and n-octane. The results of Fourier transform infrared spectroscopy confirmed that the major functional groups on the surface of H(2)O(2)-treated BaTiO(3) nanoparticles are hydroxyl groups which are chemically active, favoring chemical bonding with SOA. The results of transmission electron microscopy of SOA-modified BaTiO(3) nanoparticles suggested that the oleate molecules were bonded to the surfaces of nanoparticles and formed a homogeneous layer having a thickness of about 2 nm. Furthermore, the improved dispersion capability of the modified BaTiO(3) nanoparticles in organic solvents was verified through analytic results of its settling and rheological behaviors.     

A stability indicating assay method for cefuroxime axetil and its application to analysis of tablets exposed to accelerated stability test conditions

Cefuroxime axetil is the esterified form of cefuroxime, injectable second generation cephalosporine antibiotic that can be given orally. Stereo and structural isomers of cefuroxime axetil (CA), anti-cefuroxime axetil (ACA) and Delta(3)-cefuroxime axetil (DCA), can be present in cefuroxime dosage forms as the process related impurities as well as possible degradation product. Sensitive and precise reversed-phase high-performance liquid chromatography (RP-HPLC) method was developed and validated for the determination of cefuroxime axetil in the presence of its degradation products in solid dosage forms. The RSD values for cefuroxime axetil, anti-cefuroxime axetil and Delta(3)-cefuroxime axetil of 1.80, 1.99 and 2.48%, respectively, indicated a good precision of the RP-HPLC method. Developed RP-HPLC method was sensitive with LOD = 0.08 microg mL(-1) and LOQ = 0.60 microg mL(-1) for anti-cefuroxime axetil and LOD = 0.06 microg mL(-1) and LOQ = 0.45 microg mL(-1) for Delta(3)-cefuroxime axetil. Holding studies were carried out on Ceroxim tablets, according to ICH regulation at 30 degrees C/60% relative humidity (RH) and 40 degrees C/75% RH for 1, 2, 3 and 6 months. The review data from the stability studies conducted, show the significant content change of Delta(3)-cefuroxime axetil.     

Hydride-alkenylcarbyne to alkenylcarbene transformation in bisphosphine-osmium complexes

The elongated dihydrogen complex [formula: see text](1) reacts with 1,1-diphenyl-2-propyn-1-ol and 2-methyl-3-butyn-2-ol to give the hydride-hydroxyvinylidene-pi-alkynol derivatives [OsH{=C=CHC(OH)R2}{eta2-HC(triple bond)CC(OH)R2}(PiPr3)2]BF4 (R = Ph (2), Me (3)), where the pi-alkynols act as four-electron donor ligands. Treatment of 2 and 3 with HBF(4) and coordinating solvents leads to the dicationic hydride-alkenylcarbyne compounds [OsH((triple bond)CCH=CR2)S2(PiPr3)2][BF4]2 (R = Ph, S = H(2)O (4), CH(3)CN (5); R = Me, S = CH(3)CN (6)), which in acetonitrile evolve into the alkenylcarbene complexes [Os(=CHCH=CR2)(CH3CN)3(PiPr3)2][BF4](2) (R = Ph (7), Me (8)) by means of a concerted 1,2-hydrogen shift from the osmium to the carbyne carbon atom. Treatment of 2-propanol solutions of 5 with NaCl affords OsHCl2((triple bond)CCH=CPh2)(PiPr3)2 (10), which reacts with AgBF(4) and acetonitrile to give [OsHCl((triple bond)CCH=CPh2)(CH3CN)(PiPr3)2]BF(4) (11). In this solvent complex 11 is converted to [OsCl(=CHCH=CPh2)(CH3CN)2(PiPr3)2]BF(4) (12). Complex 5 reacts with CO to give [Os(=CHCH=CPh2)(CO)(CH3CN)2(PiPr3)2][BF(4)](2) (15). DFT calculations and kinetic studies for the hydride-alkenylcarbyne to alkenylcarbene transformation show that the difference of energy between the starting compounds and the transition states, which can be described as eta(2)-carbene species [formula: see text] increases with the basicity of the metallic center. The X-ray structures of 4 and 7 and the rotational barriers for the carbene ligands of 7, 8, and 12 are also reported.