Novel titanium precursors for homo- and co-polymerization of \u3b1-olefins: catalytic activity and materials characterization

Billions of pounds of commodity plastics, based on polyolefin resins, are produced annually and are used in wide variety of sectors in our daily lives. Despite its long history, the polyolefin industry is continuing to grow steadily and remains technologically driven because of continuous discoveries of new catalyst and applications. As a consequence polymerization of \u3b1-olefins has been one of the focus areas for catalyst research both in industry and academia. Enormous efforts have been dedicated to fine tune of the processes and to obtain better control of the polymerization and to produce tailored polymer structures. The literature review of the thesis is focused on the use of Group 4 metal complexes as precursors for \u3b1-olefin homo - and copolymerizations. More precisely, the review concentrates on the use of complexes bearing [O,O] and [O,N] type ligands which have gained considerable interest. Furthermore, the chemistry of group 4 metals complexes bearing homoleptic N,N-dialkylcarbamato ligands as potential precursors for olefin polymerization are discussed. [...

Exploration of Lewis acidity and fluorophilicity of germanium compounds and their applications in C-F bond activation

The elusive branched fluoro-oligogermane (Ph3Ge)3GeF which is the only crystallographically characterized Ge-F containing compound with unsupported Ge- Ge bonds, was successfully synthesized and its chemical/electrochemical properties studied by NMR, UV-Vis spectroscopy, CV, DPV, and DFT calculations. The key to access (Ph3Ge)3GeF is the germylium intermediate (Ph3Ge)3Ge+ that is a strong Lewis acid and is able to activate the C-X bond in CH2X2 (X=Cl, Br, I).The potential of germyliums as Lewis acids is explored in hydrodefluorination reactions. In a transition-metal-free approach, the germylium [Ph3Ge]+ generated from Ph3GeH and a catalytic amount of [Ph3C][B(C6F5)4] is able to convert aryl and aliphatic acid fluorides directly to their corresponding aldehydes without decarbonylation. The catalyst is also capable of performing the hydrodefluorination of aliphatic organofluorines.In the early attempts at C - F amination of organofluorines, it was observed that germanium amides Ph3GeNR2 exhibit a frustrated-Lewis pair-type reactivity. However, when germanium amides Ph3GeNR2 (R=TMS, Me, iPr) are reacted with acyl fluorides, it results in the direct amidation reactions to form important tertiary amides. Experimental and computational studies suggest a o-bond metathesis pathway for this reaction

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

Reactions of TaF5 with activated arenes. Synthesis of [4-(OH)-3-(OCH3)C6H3CH(OH)][4-(OH)-3-(OCH3)C6H3CHO][TaF6], a rare example of protonated aldehyde

The rare example of protonated aldehyde salt [4-(OH)-3-(OCH3)C6H3CH(=O-H)][4-(O-H)-3-(OCH3)C6H3-CHO][TaF6], 1, was isolated in the solid state by the reaction of 4-hydroxy-3-methoxybenzaldehyde (vanillin) with TaF5 in dichloromethane. The product 1 was characterized by X-ray diffraction and IR spectroscopy. The 1:1 reaction of TaF5 with N,N-dimethylaniline in CH2Cl2 cleanly afforded [TaF4(NMe2- C6H5)(2)][TaF6], 2, which was identified by NMR spectroscopy. Attempts of crystallization of 2 resulted in the isolation of the ammonium salt [NHMe2C6H5][TaF6], 3

Activation reactions of oxygen compounds by early-transition high-valent metal halides

NbF5, NbCl5, MoCl5 and WCl6 are commercial non expensive compounds, which have found large application in synthetic chemistry. However, little is still known about the direct interactions of such transition metal halides with stoichiometric amounts of organic molecules. Our recent, systematic investigation on the chemistry of NbF5, NbCl5, MoCl5 and WCl6 with oxygen donors has provided evidences of interesting and unusual features. Here we report an overview of the distinct activation routes followed by a series of simple oxygen containing molecules when contacted with the cited metal halides. The series includes natural alkoxyarenes, ketones/aldehydes, amides, and natural -aminoacids

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