Reaction products of W(CO)(6) with formamidines; electronic structure of a W(2)(mu-CO)(2) core with unsymmetric bridging carbonyls

Reactions of W(CO)(6) with formamidines contrast with those of Mo(CO)(6) and Cr(CO)(6) in that the former do not yield quadruply bonded dimetal species. From the reaction of W(CO)(6) with HDAniF (HDAniF = N,N'-di-p-anisylformamidine), several new ditungsten carbonyl compounds (W(2)(mu-CO)(2)(mu-DAniF)(2)(eta(2)-DAniF)(2) (1), W(2)(mu-CO)(2)(mu-DAniF)(2)(eta(2)-DAniF)(eta(2)-CH(2)DAniF) (2), and W(2)(mu-CO)(mu-CNC(6)H(4)OCH(3))(mu-DAniF)(2)(eta(2)-DAniF)(2) (3)) have been isolated and fully characterized. In 2, CH(2)DAniF represents a DAniF ligand in which a methylene group has been added to one of the nitrogen atoms. This ligand binds to the tungsten atom using a nitrogen and a carbon atom. Compound 1 has a tungsten-tungsten bond distance of 2.476(1) A and a planar W(2)(mu-CO)(2) core structure which has C(2)(h)() symmetry with short and long W-C bond distances (1.99(1) and 2.28(1) A, respectively). DFT calculations on a model of 1 indicate that (a) the C(2)(h)() instead of D(2)(h)() symmetry of the ditungsten core may be attributed to W --> CO pi back-bonding interactions and (b) the bond between the tungsten atoms may be formulated as a double bond. The new tetragonal paddlewheel compound W(2)(DAniF)(4) (4) and the edge-sharing bioctahedron W(2)(mu-O)(mu-NC(6)H(3)Cl(2))(mu-D(Cl)PhF)(2)(eta(2)-D(Cl)PhF)(2) (5) (D(Cl)PhF = N,N'-di-(3,5-dichlorophenyl)formamidinate) have also been prepared.     

Cleavage by halogens of carbon—cobalt bonds in organometallic complexes of cobalt(III) : III. Kinetics and mechanism of the reactions of organobis(dimethylglyoximato)cobalt(III) complexes with iodine in chloroform

The kinetics of the reaction between organocobaloximes, RCo(DH)₂H₂O, and iodine have been investigated. They reveal the participation of an RCo(DH)₂H₂O · I₂ intermediate which undergoes intramolecular transalkylation and acts as an electrophile towards a second organocobaloxime molecule. The trend in reactivity as the R group is varied is discussed.     

Synthesis of 4H-3,1-benzoxazines, quinazolin-2-ones, and quinoline-4-ones by palladium-catalyzed oxidative carbonylation of 2-ethynylaniline derivatives

An effective and straightforward approach to the synthesis of 4H-3,1-benzoxazines 3 and 4, quinazolin-2-ones 5, and quinoline-4-one derivatives 6 and 7 is provided by palladium-catalyzed cyclization-alkoxycarbonylation of variously substituted 2-(trimethylsilanyl)ethynylaniline amide or urea derivatives 2. Reactions are carried out in 7:1 MeCN/MeOH at 65 or 75 degrees C in the presence of catalytic amounts of 10% Pd/C in conjunction with Bu(4)NI and KF and under 2.4 MPa of a 3:1 mixture of CO and air. Anti and syn 6-exo-dig cyclization modes account for the formation of the two stereoisomers. Isomerization of the vinylpalladium intermediate may occur as well. Formation of a double carbonylation product 7r and of a gem-dimethoxycarbonylation product 6s, whose structures have been determined by X-ray diffraction analysis, is justified through an unusual type of rearrangement.     

DABCO-directed self-assembly of bisporphyrins (DABCO=1,4-diazabicyclo[2.2.2]octane)

Three isomeric zinc bisporphyrins have been prepared by covalently linking together two aminoporphyrins with an isophthalic acid derivative. The porphyrins differ in the substitution pattern on the meso phenyl groups, that is, ortho, meta, or para. Titrations carried out by UV-visible and 1H NMR spectroscopy have been used to map out the stabilities and the stoichiometries of the complexes formed with 1,4-diazabicyclo[2.2.2]octane (DABCO) in chloroform. The ortho- and meta-substituted bisporphyrins form 1:1 intramolecular sandwich complexes. The para-substituted bisporphyrin cannot adopt the cofacial conformation required for this type of complex and forms a higher order 2:2 intermolecular assembly, which is stable over a wide range of DABCO concentrations.     

Chloroheptakis(dimethyl sulfoxide)­uranium(IV) trichloride

In the title complex, [UCl(C₂H₆OS)₇]Cl₃, the uranium metal center is coordinated in a distorted bicapped trigonal prism geometry by seven O atoms from di­methyl sulfoxide ligands and by a terminal chloride ligand. Charge balance is maintained by three outer‐sphere chloride ions per uranium(IV) metal center. Principle bond lengths include U—O 2.391 (2)–2.315 (2) Å, U—Cl 2.7207 (9) Å, and average S—O 1.540 (5) Å.     

Density of states due to donor-pair molecules in three- and two-dimensional semiconductor systems

The density of states is calculated for a random distribution of donor-pairs of hydrogenlike impurities in three- and two-dimensional systems. Recent investigations of the hydrogen molecule in the alternant–molecular–orbital approximation are here extended. We found that the lowest excited state ¹Σu (i.e., H⁺H^?), which is optically connected to the ground state, plays a relevant role in the absorption spectra of semiconductor systems.     

Determination of copper in medicinal plants used as dietary supplements by atomic absorption spectrometry with direct flame solid analysis

An alternative device for the direct solid analysis (DSA) for copper determination by flame atomic absorption spectrometry (FAAS) is proposed. Copper was directly determined in commercial medicinal plants used as dietary supplements. The determination of copper in solid samples by DSA–FAAS was made by using a conventional air–acetylene flame. Between 0.05 and 1.5 mg of each test, sample was weighed directly into a small polyethylene vial connected to the device used for solid introduction into the flame. Test samples were introduced into the flame as a dry aerosol using a T-quartz cell set between the burner and the optical path. The T-quartz cell has a slit in the superior part by which the solid aerosol passes to the flame. A transient signal, evaluated as integrated absorbance, is produced and it is totally integrated in 2 s. Background signals always presented absorbance values less than 0.1. It was found a characteristic mass of 0.8 ng Cu and absolute limit of detection of 1.2 ng (3 s), or 1.2 μg g⁻¹ if a sample mass of 1 mg was used. Optimized conditions for air flow rate, flame stoichiometry, and so on were established as well. No excessive grinding of the samples was needed and samples with particle of size less than 80 μm were used throughout. No statistical difference between the results from the proposed system and those obtained by sample digestion and determination by conventional FAAS was observed. With the proposed procedure, more than 50 test samples can be analyzed in 1 h and it can be easily adapted to conventional spectrometers for FAAS.     

Thermal degradation of a highly chlorinated paraffin used as a fire retardant additive for polymers

The thermal degradation of a highly chlorinated paraffin, (Cl 70% w/w)(CP), used as a fire retardant additive for polymers, has been studied by TG, DTA and TVA. The main volatile degradation product is HCl which is eliminated in two steps. To 60–70% dehydrochlorination an apparent zero order reaction occurs with a detectable rate from 250°C, probably initiated at labile chlorine atoms. The apparent activation energy of the process is 40 kcal/mole. A charred residue containing 35% chlorine is obtained. This residue undergoes nearly complete dehydrochlorination in the range 300–600°C.     

Zum Nachweis der Oxyde von Molybdän,Wolfram und Vanadin

Zusammenfassung Es wird eine sehr empfindliche Reaktion zum Nachweis der Oxyde des Molybdäns, Wolframs und Vanadins angegeben. Sie beruht auf der Abscheidung von braunem Thallium(III)-oxydhydrat, aus ammoniakalischer Lösung von Thallium(I)-salzen auf Zusatz von Wasserstoffsuperoxyd und den oben genannten Oxyden, die hiebei als Katalysatoren wirken.Herrn Prof. Dr.Emil Abel, dem österreichischen Altmeister der Katalysenforschung, zum 80. Geburtstag.