A. M. Raspolli Galletti

Organometallic nickel catalysts anchored on polymeric matrices in the oligomerization and/or polymerization of olefins. Part II. Effect and role of the components of the catalytic system

Abstract Organometallic nickel complexes with bidentate P∩O chelating ligands of ylidic (ue5f8C(O)Hue5fbPPh 3 ) and phosphino-acetic (ue5f8CH(PPh 2 )ue5f8COOH) type heterogenized on polystyrene resins by anchoring through the carbon atom of the ligand have been prepared and used in the polymerization and/or oligomerization of ethylene. Their catalytic behaviour has been compared with those of corresponding homogeneous models and with heterogeneous species with the phosphine and oxygenated ligand bound in a non-chelated arrangement. The catalytic activity and selectivity are strongly dependent on the chelating strength of the ligand. The polymerization of ethylene to HDPE occurs with replica of the support morphology. The role of the ancillary ligand (phosphine, nitrogen bases, etc.) added to the systems has also been studied and clarified.

Organometallic nickel catalysts bound to polymeric matrices in the oligomerization and/or polymerization of olefins with a replica of the support morphology

Abstract Organometallic nickel complexes with bidentate P O ⌢ chelating ligands of type Ph(PPh3)Ni(Ph2PCHCOPh) were heterogenized according to a new strategy — through the =CH— group of the ylidic ligand — and their behaviour in the polymerization and/or oligomerization of ethylene investigated. When anchored to polystyrene resins the catalytic systems showed a high and very selective activity in ethylene polymerization (1–2.5 kg of polymer (g Ni)−1 h−1) working in slurry or in gas—solid phase with reproduction of the morphology of the starting resins. When the matrix is a microspherical resin (0.1–0.3 mm diameter) the HDPE (high-density polyethylene) obtained is in the form of regular and very compact spheres of 3–7 mm diameter. Depending on the physical characteristics of the matrix (crosslinking, surface area, porosity, existence of spacing groups), compact spheres, hollow spheres (‘eggs’), geminates, polymer powders, or liquid oligomers were obtained.

Striking different behavior in the activation of α-olefins by homogeneous and heterogenized catalysts based on η5-cyclopentadienyl nickel derivatives

Abstract Homogeneous η5-cyclopentadienyl nickel catalysts have been applied to ethylene oligomerization. Their activity, enhanced by the presence of Al(OEt)Et 2 as co-catalyst, resulted the highest up to now reported for this type of complexes. The same catalytic systems were also able to oligomerize propylene as well as ethylene/propylene mixtures. In particular propylene was converted into branched dimers, mostly 2,3-dimethylbutenes. Heterogenization of the above system, carried out by anchoring the nickel derivative to a styrene/divinylbenzene resin properly functionalized with the cyclopentadienyl group, caused a drastic change of the selectivity of the process, ethylene polymerization to HDPE taking place instead of oligomerization.

Direct synthesis of alcohols from n-olefins and syngas in the liquid phase catalyzed by rhodium supported on crosslinked acrylic resins

Abstract The [Rh(acac)(CO)2] complex undergoes facile coordination on macromolecular isocyanides to quantitatively give the macromolecular complex [(P℘ue5f8Nue5fcC)2Rh(acac)(CO)]. This material is the precursor of a heterogeneous, reusable catalyst able to promote the hydroformylation of 1-hexene in toluene at 120°C and 12 MPa, with subsequent quantitative hydrogenation of the aldehydes formed. No olefin hydrogenation is observed, and only minor amounts of internal hexenes are detected in the final reaction mixtures. The ratio of normal to branched products is usually close to one. Catalyst activation is accompanied by the hydrogenation of the isocyano ligand and by the reduction of Rh(I) to finely and evenly dispersed metal aggregates, with dimensions ranging from 1.6 to 7.2 nm (X-ray microprobe and TEM). It is likely that the hydroformylation reaction is catalyzed in the liquid phase by soluble rhodium hydridocarbonyl species, which form during every catalytic run. The selective reduction of the aldehydes is probably catalyzed by the polymer-supported rhodium crystallites, i.e., under real heterogeneous conditions.

Homo- and co-polymerization of styrene with ethylene by novel nickel catalysts

Abstract The homopolymerization of styrene has been studied by using catalysts based on bis(α-nitroacetophenonate)Nickel(II) [Ni(naph) 2 ] and bis(hexafluoroacetylacetonate)Nickel(II) [Ni(hfacac) 2 ] precursors and methylalumoxane (MAO) as co-catalyst. The former system displayed at room temperature a higher activity as compared with other previously reported nickel catalysts, giving rise to a substantially atactic polystyrene with a quite low molecular weight. The use of the basic and bulky tricyclohexylphosphine (PCy 3 ) as ancillary ligand allowed to increase both molecular weight (∼20,000xa0Da) and isotacticity degree (∼50%) of the polymer. On the contrary, the use of the less basic triphenylphosphine (PPh 3 ) caused a reduction of isotacticity degree. On increasing the reaction temperature at 70°C, even in absence of the phosphine ligand, both catalytic systems gave a polymer characterized by about 50% isotacticity degree. A significant further increase of isotacticity degree (65–70%) was obtained when a AlMe 3 free MAO was adopted in combination with the above nickel precursors. The GC/MS analysis of the oligomeric products allowed us to conclude that styrene insertion is mainly of secondary type. The above catalytic systems were found also to copolymerize ethylene with styrene, giving rise mainly to oligomeric products.

Hydrocarbonylation of ethyl orthoformate in the presence of rhodium catalysts

Abstract The reaction of ethyl orthoformate with a mixture of CO and H 2 ( P 8 MPa) in the presence of various rhodium carbonyl catalysts with and without iodide promoters at temperatures of 150–170°C has been studied. The [Rh(CO) 2 I 2 ] − /CH 3 I systems mainly catalyze the hydrogenation of ethyl orthoformate to diethoxymethane without any subsequent hydrogenation to methyl derivatives and methane. Carbonylation and hydrocarbonylation products of the ethyl moiety, i.e. ethyl propionate and 1,1-diethoxypropane together with diethyl carbonate coming from carbonylation of the ethoxy group, are produced, with a maximum selectivity of 12%. Chlorocarbonylrhodium systems without iodide promoters are active in the hydrogenation and hydrocarbonylation of the substrate, whereas carbonylrhodium derivatives without halide ligands and promoters only catalyze the hydrogenation to diethoxymethane. IR spectroscopic studies show that the rhodium species produced under the reaction conditions are in all cases anionic halocarbonyl or carbonyl complexes, and the course of the reaction seems to depend on the hydrido character of the parent derivative.

Homologation with CO+H2 of ethyl orthoformate in the presence of ruthenium catalysts: a stepwise hydrogenation and carbonylation reaction

The reaction of ethyl orthoformate with CO + H2 (P 10–15 MPa) in the presence of ruthenium carbonyl iodide catalysts at temperatures of 130–200°C has been studied. Products of hydrogenation, carbonylation and homologation of the CH, Et and EtO moieties of the ester are formed, indicating that the catalyst can activate the substrate in three ways. Diethoxymethane was the main product at lower temperatures, whereas methyl ethyl ether, methanol, and ethyl propionate predominate at higher temperatures. The formation of significant amounts of diethyl carbonate and diethoxyethane indicates the intermediate formation of EtO-Ru derivatives. Results of experiments with CO + D2 suggest a step-wise process of hydrogenation and carbonylation of the substrate, and shed new light on the mechanism of activation of esters by ruthenium carbonyl iodide catalysts.

Characterization of magnetite nanoparticles

This paper deals with the chemical preparation and magnetic characterization of nanoparticles of magnetite. A new hydrothermal synthesis of magnetite is adopted to prepare samples with different particle sizes and magnetic measurements are performed in two different laboratories adopting two different measurement methods. The saturation region is investigated by a vibrating sample magnetometer, while the behavior of minor cycles is mainly studied via an inductive method. An investigation is carried out on the magnetic behavior of a commercial magnetite together to an analysis of its crystal structure by X-Ray diffraction method and TEM micrographs. Some critical aspects relevant to the characterization of nanopowders by the two measurement methods are discussed throughout the paper.

Hydrogenolysis of formic esters with homogeneous and heterogeneous rhenium catalysts

Abstract The hydrogenolysis of formic esters to methanol, as the second step of the low temperature methanol synthesis from syngas, has been studied using rhenium catalysts. ‘Rhenium blacks’ containing reduced Re(0) species produced ‘in situ’ starting from soluble rhenium precursors like Re 2 O 7 or Re 2 (CO) 10 are active and generally very selective (99%) in the hydrogenation of the formyl group to methanol. Unfortunately this catalyst suffers from CO poisoning: however, the poisoning is reversible and the catalytic activity can be restored by treatment with pure hydrogen. Rhenium catalysts supported on oxides generally are less active and selective: the acid or basic centres of the support, which strongly interact with the oxophilic rhenium cations, make difficult the generation of the active Re(0) species and on other hand promote the decarboxylation of the formic ester.

Measuring the magnetic properties of Fe 3 O 4 nanopowders

An inductive measurement method was adopted to analyze the magnetic properties of magnetite nanopowders and the possibility to prepare samples having the same geometry is discussed from a macroscopic point of view. The influence of the chemical composition on magnetic and morphological characteristics of the samples was investigated by several measurement techniques with the aim to better investigate the observed magnetic effects. An innovative green Micro-Wave (MW)-assisted approach was used for the synthesis of magnetite (Fe3O4) nanopowder and of magnetic bimetallic systems M@Fe3O4 (M: Ru or Pd) and the effect of noble metals was observed. The structure and chemical identification of the synthesized materials were analyzed and correlated to the measured magnetic properties.