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

Highly 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

Thermal and structural investigation of random ethylene/1-hexene copolymers with high 1-hexene content

Random 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

Homopolymerization of n-butyl methacrylate by bis(salicylaldiminate)Cu(II)/MAO catalysts

Polymn. catalysts based on copper precursors appear particularly interesting due to the low metal cost, limited toxicity and modest sensitivity to deactivation by polar species. To date, .alpha.-olefin and polar monomer coordination polymn. catalyzed using copper catalysts has been scarcely investigated, and a good part of the literature is represented by patents. Here this research has been expanded to the study of the performances of bis(salicylaldiminate)copper(II)/methylaluminoxane (MAO) catalysts in the polymn. of Bu methacrylate. The study of the catalytic activity of bis(salicylaldiminate)copper(II)/MAO systems in Bu methacrylate polymn. was focused on the relationship between the catalytic behavior and the main reaction conditions and ligand structures. The electronic and steric characteristics of the chelate ligands play an important role in the catalytic performances. The presence of electron-withdrawing nitro groups on the chelate ligands increased the catalytic activity which reached 36 kgpolymer mol-1 h-1, the highest value up to now reported for copper systems in methacrylic or acrylic monomer polymn. These performances were ascribed to copper catalysts activated by MAO: without copper precursor, working in the presence of MAO and free salicylaldimine ligand, complete inactivity was ascertained

Unusual activations of oxygen molecules by early transition metal chlorides

NbCl5, 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 CN coupling and yields acylamidinium salt in mild conditions (Figure 2)

Synthesis, X-ray Characterization, and Reactivity of a-Aminoacidato Ethoxide Complexes of Niobium(V) and Tantalum(V)

High yields of the ethoxo-a-aminoacidates of general formula M(OEt)4[C(O)CHRNHR\u2019-O,N] (M = Nb, R = CH2Ph, R\u2019 = H, 2; R = CHMe2, R\u2019 = H, 3; R = CH2CHMe2, R\u2019 = H, 4; R = H, R\u2019 = Me, 5; R = CH2CH2SMe, R\u2019 = H, 6; M = Ta, R = CH2Ph, R\u2019 = H, 7; R = CH2CH2SMe, R\u2019 = H, 8) and M(OEt)4( -\uf06bO,\uf06bN) (M = Nb, 9, Ta, 10) have been obtained by the reaction of the L-enantiopure \uf061a-amino acid (or sarcosine) with a slight molar excess of M(OEt)5 (M = Nb, 1a; Ta, 1b) in dichloromethane solution. The new complexes 2-10 have been fully characterized by spectroscopic and analytical methods, and by X-ray diffraction in the cases of 2, 7, 8 and 9. Such X-ray structures are the first ones ever reported for niobium and tantalum coordination compounds containing an \uf061-aminoacidato ligand. The early-late heterobimetallic derivative Ta(OEt)4[O2CCH(NH2)CH2CH2S(CH3)(AuCl)], 11, has been prepared by the reaction of 8 with the stoichiometric amount of Au(CO)Cl. The bulk polymerization of D,L-lactide initiated by complexes 2 and 7 gave a slightly heterotactic enchainment (Pr = 0.54 and 0.63 respectively) whereas complexes 1a and 1b formed fully atactic PLA with Pr 48 0.4

Synthesis of di- and tetranuclear oxidomolybdenum (V) complexes containing p-toluenesulfonates as ligands: a joint spectroscopic, crystallographic and computational study

The 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

Niobium And Tantalum Alkoxide Complexes With Natural Amino Acids: Synthesis, Structure And Lactide Polymerization Behaviour

In Libro degli Abstrac