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Highly Active and Easily Accessible Catalysts for Vinyl Polymerization of Norbornene Obtained by Oxidative Addition of Salicylaldimine Ligands to Bis(1,5-cyclooctadiene)nickel(0) and Methylaluminoxane
No full textHighly active, cheap, and easy to synthesize catalytic
systems, obtained in situ by the oxidative addition of salicylaldimine
ligands to bis(1,5-cyclooctadiene)nickel(0) and
activated by methylaluminoxane (MAO), are now reported for
the vinyl polymerization of norbornene. Their activity resulted
mainly influenced by the nature of the substituents present
both on the phenolate moiety and on the N-aryl ring as well as
the content of free trimethylaluminum (TMA) present in the
commercial MAO. In particular, the maximum activity, up
to about 78,000 kg polynorbornene/mol Ni h, was ascertained
when 3,5-dinitro-N-(2,6-diisopropylphenyl)salicylaldimine
ligand was adopted in conjunction with Ni(cod)2 and
TMA-depleted MAO. This remarkable performance, to the best
of our knowledge, the highest never reported working in toluene
instead of chlorinated aromatics, was reached adopting
this more sustainable reaction medium. The influence of the
main reaction parameters such as reaction time, temperature,
monomer/Ni, and Al/Ni molar ratios on the catalytic performances
and polymer characteristics was studied as well
Niobium And Tantalum Alkoxide Complexes With Natural Amino Acids: Synthesis, Structure And Lactide Polymerization Behaviour
No full textIn Libro degli Abstrac
Reactions of Molybdenum Pentachloride with Oxygen and Nitrogen Donor Ligands
No full textThe interactions of MoCl5 (1) with a variety of organic compounds were studied in dichloromethane and the metal products were isolated in the solid state. The 3:1 molar reactions of 1 with OCRR′ (R = R′ = Ph, R = H, R′ = 2-C6H4Me) afforded the complexes Mo(O)Cl3(OCRR′)2 (R = R′ = Ph, 2a; R = H, R′ = 2-C6H4Me, 2b) in high yields. Compound Mo(O)Cl3[ ], 3, was isolated in 35% yield from 1 and 2-acetylfuran. The 1:1 reactions of 1 with, respectively, MeO2CCCCO2Me and phenazine (C12H8N2) resulted in the formation of the polynuclear complexes [MoCl4:2-L]n (L = MeO2CCCCO2Me, 4; L = C12H8N2, 6). The mononuclear Mo(O)Cl3[1(N)-C12H8N2], 7, was prepared straightforwardly by addition of phenazine to Mo(O)Cl3, formed in situ upon treatment of 1 with tetrahydrofuran. The 1:2 reaction of 1 with Me2NCH2CH2CO2Me gave MoCl4[1(N)-Me2NCH2CH2CO2Me]2, 5, in 72% yield. The molecular structures of 2a, 3 and 7 were elucidated by X-ray diffraction studies; the X-ray structure of 7 represents a rare example of crystallographically-characterized pentacoordinated Mo(V) complex
Synthesis of di- and tetranuclear oxidomolybdenum (V) complexes containing p-toluenesulfonates as ligands: a joint spectroscopic, crystallographic and computational study
No full textThe 1 : 1 reaction of MoCl5 with 1,4-Me(SO3Me)C6H4 led to the isolation of crystalline Mo2O2Cl6[μ–κ2-
1,4-Me(SO3Me)C6H4], 1, in low yields. Attempts to reproduce the synthesis of 1 from MoOCl3/1,4-Me
(SO3Me)C6H4 resulted in the good-yield formation of [MoOCl2(μ-Cl)(κ1-1,4-Me(SO3Me)C6H4)]2, 2. The
1 : 1 reaction of MoCl5 with 1,4-Me(SO3H)C6H4·H2O selectively yielded Mo4O4Cl8[μ3-1,4-Me(SO3)C6H4]4,
3. Compounds 1 and 3 were characterized by X-ray diffractometry; moreover DFT calculations were
carried out on 1–3 in order to shed light on their thermodynamic and structural features
Thermal and structural investigation of random ethylene/1-hexene copolymers with high 1-hexene content
No full textRandom ethylene/1-hexene copolymers with the 1-hexene content in the range from 2 to 28 mol% were produced with a novel post-metallocene catalyst and analyzed by three techniques, FTIR, 13C NMR, and DSC. The 1-hexene content and the sequence distribution in the copolymers were determined by means of FTIR-M and 13C NMR. The crystallization behavior of the copolymers was studied by DSC under dynamic and isothermal conditions; the Avrami model was used to analyze the crystallization kinetics. It was found that both the 1-hexene content and the crystallization temperature affect the relative crystallinity. The bulk crystallization rate decreases with the 1-hexene content and reduces exponentially with an increase of T c. The melting behavior of isothermally crystallized samples was also investigated and it was found that the melting temperatures of the copolymers under equilibrium conditions were related to the compositio
Activation Reactions of Oxygen-Containing Organic Molecules by High Valent Metal Halides of Groups 5-6
No full text
Unusual activations of oxygen molecules by early transition metal chlorides
No full textNbCl5, MoCl5 and WCl6 are commercial non expensive compounds, which have found application in material and synthetic chemistry. Nonetheless the knowledge about the direct interaction of these transition metal halides with stoichiometric amounts of organic molecules is far from being well understood. Recently, our systematic study on the chemistry of MX5 (M = Nb, Ta; X = halide) with oxygen donors has provided evidence of interesting and unusual features.1 Here we report the distinct activation routes followed by a series of simple carbonyl-containing molecules when contacted with the cited chlorides. For instance, natural aminoacids are deoxygenated by MoCl5, whereas rare decarboxylation to iminium may occur with NbCl5 (Figure 1). Furthermore WCl6 acts as efficient chlorinating agent towards ketones and amides. In particular, the reaction with acetanilide proceeds with CN coupling and yields acylamidinium salt in mild conditions (Figure 2)
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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