Luca Rosi

Ruthenium carbonyl carboxylates with nitrogen containing ligands: IV. Catalytic activity in the hydroformylation of olefins in homogeneous phase☆

Abstract Ruthenium carbonyl acetato complexes containing bipyridines or phenantrolines ligands are tested as catalysts in the hydroformylation of hex-1-ene in homogeneous phase. These catalysts are active also in solutions containing water and the selectivity to aldehyde is high. Only a moderate hydrogenation of the alkene occurs. The regioselectivity to the linear aldehyde reaches 85.7% when using the mononuclear complex containing 4,7-dmphen as ligand. In the course of the reaction the starting olefin is largely isomerized.

The role of functionalized phosphines in the hydrogenation of carboxylic acids in the presence of phosphine substituted hydrido ruthenium complexes

Hydrido ruthenium carbonyl complexes substituted by functionalized phosphines such as H4Ru4(CO)8[P(CH2OCOR)3]4 have been synthesized and tested as catalysts in the hydrogenation of carboxylic acids. These complexes are more active than those reported previously, containing trialkyl- or triarylphosphines. On the basis of their behavior, their different activity has been explained in terms of an involvement of the phosphine ligand in the catalytic cycle. The ester group present in the phosphine P(CH2OCOR)3 is hydrogenated to produce an alcohol (RCH2OH) and a P(CH2OH) group which, in turn, reacts with the free acid present in solution to restore the P(CH2OCOR) group. This hypothesis has been confirmed by the reactivity of the possible intermediate H4Ru4(CO)8[P(CH2OH)3]4 with acetic acid. Another support to this statement is the almost equal catalytic activity, displayed by H4Ru4(CO)8[P(CH2OCOR)3]4 complexes, whatever the R group present, in the phosphine ligand, in the hydrogenation of carboxylic acids. These complexes, on the other hand, are less active than the corresponding tributylphosphine substituted ones in the hydrogenation of alkenes and ketones. Finally when the phosphine ligand is P(CH2CH2COOCH3)3 the ester group is not reduced and consequently the catalytic activity of this complex in the hydrogenation of carboxylic acids is very low.

Functionalized phosphine substituted cobalt carbonyls. Synthesis, characterization and catalytic activity in the hydroformylation of olefins

Abstract Four tertiary phosphines containing functionalized alkyl groups P(CH 2 CH 2 CN) 3 , P(CH 2 CH 2 CO 2 CH 3 ) 3 , P(CH 2 CH 2 CH 2 OCH 3 ) 3 and P(CH 2 CH 2 CH 2 OCH 2 CH 3 ) 3 have been synthesized and used as ligands in Co 2 (CO) 6 (L) 2 complexes which were fully characterized. The catalytic activity of these cobalt complexes in the hydroformylation of hex-1-ene and propene was tested. The influence of several parameters such as type of solvent, reaction temperature, carbon monoxide partial pressure, excess of free phosphine in solution, on the chemio- and regioselectivity of the reaction were investigated. These results are compared with those obtained when using Co 2 (CO) 8 or Co 2 (CO) 6 (PBu 3 ) 2 as catalytic precursors. The hydroformylation of hex-1-ene in the presence of the above complexes has been rationalized on the basis of the mechanism suggested for the hydroformylation of propene in the presence of Co 2 (CO) 6 (PBu 3 ) 2 .

L-Lactide polymerization by calix[4]arene-titanium (IV) complex using conventional heating and microwave irradiation

Abstract Since the first contributions by Gedye and Giguere in 1986, growing attention has been registered on the use of microwave heating in organic synthesis. However still many aspects need to be clarified especially about the so called “microwave effect” and the possible degradation phenomena that may be recognized during polymer synthesis. In this work the complex cone-25,27- dipropyloxy-26,28-dioxo-calix[4]arene titanium (IV) dichloride (1) has been tested for the ring opening polymerization of L-lactide, comparing the effect of conventional heating with a possible microwave assisted strategy. The polymers obtained were fully characterized (NMR, IR, HPLC-SEC, DSC, MALDI-TOF and WAXD analysis). As expected the use of microwave irradiation induced an increase of the polymerization rate. On the other side the use of microwaves resulted in a slight loss of the control over molecular weight and molecular weight distribution if compared with a conventional thermal treatment.

Oligomerization of aldehydes catalyzed by cobalt carbonyl complexes

Abstract The catalytic activity of Co 2 (CO) 6 L 2 complexes (L=carbon monoxide, phosphines) has been tested in the oligomerization of aldehydes under the conditions adopted for hydroformylation of olefins. The influence of the type of substrate, phosphinic ligand and reaction temperature has been investigated. The products formed are β -hydroxyaldehydes, α , β -unsaturated aldehydes and β -hydroxyesters. Very poor catalytic activity was shown by cobalt complexes in the oligomerization of ketones. The role of cobalt carbonyl complexes in the aldehyde oligomerization has been rationalized by a mechanism, in which acylcobalt intermediates are involved.

Microwave pyrolysis of polymeric materials

The consumption of polymeric materials is growing ceaselessly in the world even in spite of the financial crisis. World’s plastics production in 2009 was 2.3·108 tons and in Europe it was 4.5·107 tons whose 54% is disposed as waste. The annual average production of tires in Europe is more than 2.5 106 tons. In the 2008 in Italy were produced 3.5·106 tons of plastics among which 4.1·105 tons of tires, and 1.5·106 of waste plastics tons were collected for disposal. (Chen et al., 2007; Federazione Imprese e Servizi, Unione Nazionale Imprese Recupero [FISE UNIRE], 2009; PlasticsEurope, 2010). World rubber demand is foreseen to increase up to 4% annually to 26.5 million metric tons in 2011 (Freedonia, 2010). Therefore the disposal of waste polymers is a serious environmental problem against which public is becoming more aware. The interest of waste polymeric materials disposal is focused on new uses rather than land filling or incineration. Regarding scrap tires, a strong attention has been paid over last years to the claims for their recycling or reprocessing. In consideration of their complex composition, slow degradation rate in landfill, high calorific value and shape hindrance they may be burned hardly but otherwise they cannot send to landfill anymore and an alternative methodology must be eligible in order to dispose scrap tires. European Directive No. 31/1999 states that the disposal of scrap tires in landfills is banned with the exclusion of bicycle tires and tires with an external diameter greater than 1400mm. Since July 2006 the ban has been extended also to shredded tires. Waste plastics and tires are very attractive as a source of renewed raw materials and chemical substances. These products may be achieved by pyrolysis, heating usually in the absence, but sometimes in the presence, of an oxidative agent, and these processes may be viewed as a promising technology. The pyrolysis of polymeric materials or plastic-containing wastes including scrap tires is a possible answer to the problem of their disposal because it let recover of gas, oil and solid able to be employed as a source of products and energy. Therefore the relevance of the pyrolysis processes of plastic waste has been growing. A plethora of studies over the thermal degradation of polymeric materials are carried out using conventional heating method with internal or external heating source, under inert or oxidizing atmosphere. Generally the thermal decomposition needs operating temperature above 450°C (Kaminsky et al., 2004; Mastral et al., 2002; Whesterhout et al., 1998).

The behaviour of n- and iso-propylcobalt tricarbonyl tributylphosphine complexes under hydroformylation conditions

Tributylphosphine n-propyl-(Ia) and iso-propyl (Ib) cobalt tricarbonyl have been prepared from NaCo(CO)3(PBu3) and the proper alkyl halide. The behaviour of Ia and Ib under hydroformylation conditions (T = 120–180°C, pCO = 5 atm, pH2 in the presence or absence of an excess of an olefin or PBu3) has been tested. Ia and Ib gave the expected isomeric alcohols with a selectivity higher than 95%. The role of these complexes in the hydroformylation reaction has been discussed.

Ring-Opening Polymerisation of rac-Lactide Using a Calix[4]arene-Based Titanium (IV) Complex

cone-25,27-Dipropyloxy-26,28-dioxo-calix[4]arene titanium (IV) dichloride (1) has been assessed in the ring-opening polymerisation of rac-lactide (L,D-LA). The polymers formed (PLDA) turned out to display an isotactic stereoblock microstructure (determined by NMR) despite the fact that the catalyst has symmetry. Two techniques were applied for initiating the polymerisation reaction, microwave irradiation, and conventional thermal treatment. The polymers obtained were all characterised by NMR, IR, HPLC-SEC, DSC, and MALDI-TOF analysis. The use of microwave irradiation, applied for the first time to calixarene-based catalysts in the presence of the rac-lactide monomer, increased the polymerisation rate compared with that obtained by the other method. On the other hand, standard thermal treatment enabled a slightly better control than microwave irradiation over the molecular weight and molecular weight distribution of the polylactides formed.

Synthesis and processing of biodegradable and bio-based polymers by microwave irradiation

Biodegradable polymers, as well as polymers produced from renewable feedstocks, are attracting increasing interests as possible substitutes for conventional plastics: a higher energy efficiency in synthesis and processing steps must be continuously pursued in order to maximize the intrinsic environmental benefits brought by this class of materials. Microwave assisted organic synthesis (MAOS) is nowadays a major topic in green chemistry and a great (yet rising) number of papers can already be found that report striking advantages over conventional thermal heating. Nonetheless microwave (MW) energy sources are recently being chosen also for several polymerization reactions. Indeed, reduced heating times and superior homogeneity provided by MW reactors may play a central role in optimizing production processes, with a dramatic improvement in the environmental performance. In the introduction of this chapter we’re briefly recalling some theoretical principles of microwave-matter interaction; several experimental setups are then examined and, eventually, thermal and non-thermal specific microwave effects are described and commented. The following paragraph is dedicated to a comprehensive survey of synthesis examples found in scientific literature and categorized by polymerization technique, in which particular relevance is given to products of increasing commercial importance like poly(e-caprolactone) (PCL) and poly(lactic acid) (PLA). A third part of the chapter deals with the employment of microwave heating for chemical modification and processing of polymers; the last paragraph summarizes advantages and drawbacks of microwave assisted polymer chemistry, stressing the energy efficiency topic and drawing conclusions.

Methyl acrylate polymers as suitable materials for the conservation of stone: performance improvements through atom transfer radical polymerization

Acrylic polymers are a suitable category of materials for application in building stone conservation mainly due to their peculiarities (i.e., easy to apply, low cost, good adhesive and cohesive properties, and high solubility in many organic solvents). The performances of polyacrylates have been improved through atom transfer radical polymerization (ATRP). Polymers were obtained with low polydispersity, controlled molecular weight, and showing better stability to UV irradiation than products obtained by radical polymerization. New poly(methyl acrylate-co-perfluoropolyethers) were also prepared via ATRP, using a perfluoropolyether derivative as initiator, showing the possibility of synthesizing copolymers between acrylates and perfluoropolyethers in common solvents. Protective efficiency of poly(methyl acrylate-co-perfluoropolyether) was close to that of commercially available products.