Giorgio Valentini

Role and effect of promoters of the ruthenium catalysts in the homologation of methyl acetate to ethyl acetate

Abstract The role and the effect of iodide promoters on the catalytic activity and selectivity of the ruthenium-catalyzed homologation of methyl acetate to ethyl acetate was studied. A significant cation effect in determining the distribution of the reaction products was observed. Alkaline cations and ammonium or tetraalkylammonium cations favour the simple carbonylation reaction rather than the homologation, improving the selectivity to acetic acid but also decreasing the formation of secondary products. The water formed in the homologation reaction is mostly consumed in the water-gas shift reaction, which is also favoured by the presence of alkaline or ammonium cations.

Role of the polymeric ligand in determining the catalytic activity of Ru(II) and Rh(I) complexes bound to vinyl ether/maleic acid alternating copolymers

Abstract Ruthenium(II) and rhodium(I) complexes with alternating copolymers of maleic acid and different alkyl and aryl vinyl ethers have been prepared starting from RuH2(CO)(PPh3)3 or RhH(CO)(PPh3)3. The carboxylic groups of the maleic co-units functioned as ‘monodentate’ or ‘bidentate’ ligands for anchoring the metal complexes to macromolecular carriers having chemical and physical properties depending on the hydrophobicity, electronegativity, and bulkines of the ether co-units. The importance of the primary and secondary structures of the polymers in determining the distribution of metal species and the catalytic properties of the heterogeneous systems was demonstrated in a series of catalytic experiments carried out in different reaction media. The drop of the catalytic activity of the Ru derivatives and the progressive activation of the Rh systems observed in successive catalytic cycles were related to chemical modifications of the polymer-bound metal species. RuCl2(PPh3)3 was used to obtain heterogenized complexes through reaction with the sodium salts of poly(acrylic acid) and ethylene/maleic acid alternating copolymer. These last systems exhibited a practically constant catalytic activity with time.

Solid state reactions of RhCl(PPh3)3: an XPS study

Rh(I) complexes frequently used as catalysts reveal from XP spectra systematically the presence of oxidized species on the surface. As a sample system the phenomenon has been studied in greater detail on the Wilkinson compound RhCl(PPh3)3. XPS data are reported and discussed along with hypotheses on the structure of the oxidized species, taking into account peculiar features showing similarities to Rh(III) species. A series of solid state reaction, whose behaviour has been followed by means of XPS, is discussed, including air oxygenation, oxygen removal by H2 under mild conditions, and displacement reactions by strong π-acceptor ligands (CO, C2H4) leading to stable Rh(I) substitution products.

Ruthenium(II) and rhodium(I) complexes bound to poly-carboxylate and poly-β-diketonate matrices: Synthesis and catalytic activity

Abstract Complexes of ruthenium(II) and rhodium(I) with linear polymeric ligands such as poly(acrylic acid), some alternate copolymers of maleic acid with vinyl monomers (ethylene, benzylvinylether, and vinyl alcohol) and poly-β-diketones (polymethacroylacetone) have been prepared starting with RuH2(PPh3)4, RuH2CO(PPh3)3, and RhH(PPh3)4. The coordination of the metal units to the macromolecular matrices occurs with displacement of one hydride group and, on the average, of more than one triphenylphosphine ligand per metal atom. The “coordinatively unsaturated” metal species so formed along the polymeric matrices give to these complexes high catalytic activity in hydrogenation and isomerisation of olefins under mild conditions.

Surface oxidation of some Rh(I) compounds and some polymer-supported Rh(I) catalysts

Several Rh(I) compounds used in homogeneous hydrogenation and isomerization catalysis and some of their heterogenized derivatives have been investigated by the X-ray photoelectron spectroscopy (XPS) technique. XPS measurements both on polymer-bound rhodium complexes and on mononuclear Rh(I) complexes with monomeric ligands taken as reference compounds and used as precursors in the preparation of heterogenized catalysts, as well as some other Rh complexes structurally similar to such precursors, show, from Rh 3d spectra, the presence of several oxidation states of rhodium (i.e., +1 and higher), the higher oxidized being generally the major component in the surface layers. The extent of the oxidation phenomenon increased with time and was dependent on the structure and nature of ligands (e.g., RhCl(CO)(PPh3)2 being the most stable toward surface oxidation).

Polymer effect on catalysis by macromolecules/transition metal complexes

Abstract The present status of research in the field of macromolecules/transition metal complexes is critically reviewed on the basis of selected examples both from the authors′ laboratories and other laboratories around the world. The substantial lack of inertness of the polymeric ligand (the polymer effect) is examined and shown to occur in most cases during preparation of the macromolecule/transition metal complex as well as during its catalytic use. This behavior is attributed and confirmed as due to the polydentate ligand character of the macromolecules and to the effect of physical and chemical parameters which can be varied over large ranges. Future work is duscussed for the development of the field in suitable directions.

Carbonylation and Homologation of Methanol, Methyl Ethers and Esters in the Presence of Ruthenium Catalysts

Different transition metal compounds in conjunction with suitable promoters have been reported in the literature to catalyze the alcohols homologation (1–9)(Equation 1).

Some aspects of the reactivity of rhodium(I) and rhodium(II) tricyclohexylphosphine derivatives studied by ESR spectroscopy II. Formation of a paramagnetic Rh(II) carbonyl species by treatment of RhCl2(PCy3)2 in the solid state with carbon monoxide

Abstract The behaviour of RhCl(PCy 3 ) 2 in the solid state towards O 2 , Co, and H 2 was investigated. Whereas no reaction occurred with dioxygen and dihydrogen, treatment with carbon monoxide led to the formation of RhCl 2 (CO)(PCy 3 ) 2 , which is the first example of a paramagnetic carbonyl Rh(II) derivative. The product is rather labile but the life-time in the solid state was long enough to allow the spectroscopic study of the decay process. ESR and IR spectra indicated a disproportionation reaction to Rh(I) and Rh(II) carbonyl species.

Five-coordinated metal complexes of bis(2-hydroxy-1-naphthylideneimine-3-propyl)amine and their reactivity towards dioxygen. Part I. An electrochemical investigation on manganese(II), iron(II), cobalt(II), nickel(II) and copper(II) complexes

Abstract The electrochemical behaviour in aprotic solvent of the complexes {M[bis-(2-hydroxy-l-naphthylideneimine-3-propyl)amine]}, where M = Mn(II), Co(II), Fe(II), Ni(II) and Cu(II) is reported. The complexes were prepared and characterized by elemental analysis, infrared and visible spectroscopy and magnetic susceptibility measurements. In addition the reactivity towards dioxygen of the Mn(II), Fe(II) and Co(II) derivatives was investigated, mainly by cyclic voltammetry and gas-volumetric uptake measurements. The results indicate that the Co(II) complexes are able to add dioxygen reversibly, while Mn(II) and Fe(II) compounds undergo an irreversible oxygenation process. The pathway of the dioxygenation processes is tentatively interpreted on the basis of the electrochemical responses. The results confirm that the location of the oxidation potential allows one to predict whether a compound is able to react with dioxygen, but it is not sufficient to predict whether the dioxygenation reaction proceeds reversibly.

Application of microwave irradiation for the removal of polychlorinated biphenyls from siloxane transformer and hydrocarbon engine oils

The removal of polychlorinated biphenyls (PCBs) both from siloxane transformer oil and hydrocarbon engine oil was investigated through the application of microwave (MW) irradiation and a reaction system based on polyethyleneglycol (PEG) and potassium hydroxide. The influence of the main reaction parameters (MW irradiation time, molecular weight of PEG, amount of added reactants and temperature) on the dechlorination behavior was studied. Promising performances were reached, allowing about 50% of dechlorination under the best experimental conditions, together time and energy saving compared to conventional heating systems. Moreover, an interesting dechlorination degree (up to 32%) was achieved for siloxane transformer oil when MW irradiation was employed as the unique driving force. To the best of our knowledge, this is the first time in which MW irradiation is tested as the single driving force for the dechlorination of these two types of PCB-contaminated oils.