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. [...

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

Coordination chemistry of niobium and tantalum pentahalides: unusual activation reactions of simple organic molecules

Niobium and tantalum compounds lived for long time in the shadow of metal complexes of group 4, probably for the extremely interesting applications of the latter in alkene transformations. In this context, the chemistry of niobium and tantalum pentahalides was scarcely explored in the past. However, in the last decade, such commercial compounds have found increasing use in homogenous catalysis, encouraged by their easy availability and the non toxicity of the metal elements. The direct interaction of MX5 (M = Nb, Ta; X = F, Cl, Br) with limited amounts of simple organic molecules has been recently elucidated by a systematic investigation, aimed to contribute to the progress of the related catalytic processes. In some cases, the formation of coordination complexes, especially with O-donors, represents the first step of an activation process, which is usually driven by the nature of the halide. We report an overview of the main activation reactions, involving for instance carbonyl compounds, -aminoacids, arenes, etc

Reactivity of α-aminoacids with high valent transition metal halides

Studies on the interaction of high valent transition metal halides with α-amino acids are surprisingly rare. This contrasts with the observation that α-amino acidato complexes of transition metals in low-to-medium oxidation state may exhibit valuable properties in very different fields. We have been recently involved in the chemistry of α-amino acids with niobium and tantalum pentahalides, molybdenum pentachloride and tungsten hexachloride. The reactions may proceed selectively according to different routes, including O/halide interchange, decarboxylation and unprecedented condensation of α-amino acid units via CC bond formation. These results will be presented in the light of the peculiar features of the distinct metal halide reactants

Reactions of molybdenum pentachloride with oxygen and nitrogen donor ligands

The interactions of molybdenum pentachloride (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\u2032 (R = R\u2032 = Ph; R = H, R\u2032 = 2-C6H4Me) afforded the complexes Mo(O)Cl3(OCRR\u2032)2 (R = R\u2032 = Ph, 2a; R = H, R\u2032 = 2-C6H4Me, 2b) in high yields. Compound , 3, was isolated in 35% yield from 1 and 2-acetylfuran. The 1:1 reaction of 1 with phenazine (C12H8N2) 1 resulted in the formation of MoCl5(C12H8N2), 4; the oxydo-chloride derivative Mo(O)Cl3[\u3ba1(N)-C12H8N2], 5, was prepared straightforwardly by addition of phenazine to Mo(O)Cl3, formed in situ upon treatment of 1 with tetrahydrofuran. The addition of a twofold excess of Me2NCH2CH2CO2Me to 1 afforded MoCl4[\u3ba1(N)-Me2NCH2CH2CO2Me]2, 6, in 72% yield. The reaction of 1 with MeO2CCtriple bond; length of mdashCCO2Me led to a mixture of inseparable products: MoOCl3(\u3ba1-MeO2CCtriple bond; length of mdashCCO2Me)2, 7a, MoCl5(\u3ba1-MeO2CCtriple bond; length of mdashCCO2Me), 7b, and MoCl4(\u3ba1-MeO2CCtriple bond; length of mdashCCO2Me)2, 7c, were recognized by combined EPR/DFT investigation. Analogous DFT/EPR studies were performed on 2b and 4. The X-ray structures of 2a, 3 and 5 were determined; the X-ray structure of 5 represents a rare example of crystallographically-characterized pentacoordinated Mo(V) neutral complex

Activation Reactions of Oxygen-Containing Organic Molecules by High Valent Metal Halides of Groups 5-6

NbF5, NbCl5 and WCl6 are commercial non expensive compounds, which have found large application as catalytic precursors in synthetic organic chemistry. However, the direct interactions of such transition metal halides with stoichiometric amounts of organic reactants has been limitedly explored. Our recent, systematic investigation on the chemistry of NbF5, NbCl5 and WCl6 with oxygen donors has provided evidences of unusual features: 1) such halides are capable of directing mild conditions transformations, which are not commonly achieved by means of other transition metal compounds; 2) NbX6- (X = F, Cl) and WOCl5 are easily obtained and may allow the isolation of unstable organic cations. Examples will be provided with particular reference to natural -aminoacids, such as L-proline

Molybdenum(V) and molybdenum(IV) coordination compounds from the reactions of MoCl<inf>5</inf> with sulfones

The mononuclear complexes MoCl5L (L = 2,5-dihydrothiophene-1,1-dioxide), 1, and MoCl4L2 (L = dimethylsulfone, 2; diethylsulfone, 3; diphenylsulfone, 4) were obtained by the reactions of MoCl5 with the corresponding sulfones at room temperature in dichloromethane, and were characterized by analytical and magnetic data, and by X-ray crystallography in the cases of 1 and 2. The X-ray structure of 1 is the first one ever reported for an adduct of MoCl5 with a carbon-containing species

The Potentiality of High Valent Metal Halides of Groups 5-6 in the Activation of Organic Molecules

NbF5, NbCl5 and WCl6 are easily-available compounds, whose direct interaction with organic reactants was scarcely explored up to recent years. Our investigation on this piece of chemistry has provided evidence of unusual features: 1) the cited halides are capable of directing mild conditions transformations, which are not commonly achieved by means of other transition metal compounds [1]; 2) NbF5, NbCl5 and WCl6 can act as one-electron oxidants towards a variety of organic molecules, resulting in the formation of salts containing reactive cations [2]; 3) such salts may be stabilized by inert, high valent metal haloanions which are generated in situ. Examples will be provided with reference to natural -aminoacids (see Figure 1), alkoxy-arenes, alkyl-ureas and amines