Search

Bis(salicylaldiminate)copper(II) complexes, when activated with methylaluminoxane, catalyzed the homo- and copolymerizations of ethylene and methyl methacrylate (MMA). The activity in the MMA homopolymerization was influenced by the electronic and steric characteristics of the Cu(II) precursors as well as the cocatalyst concentration. The same systems revealed modest activity also in the homopolymerization of ethylene, giving a highly linear polyethylene, and in its copolymerization with MMA. These copolymers exhibited a very high content of polar groups (MMA units > 70 mol %) and were characterized by a high molecular weight and polydispersity. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1134–1142, 2007

The polymerization of norbornene in the presence of different bis(salicylaldiminate)copper(II) complexes and methylalumoxane has been investigated. In all cases a high molecular weight vinyl-type polymer was obtained. The presence of electron-withdrawing nitro groups on the chelate ligand markedly increased the activity of the catalyst. The influence on the catalytic performances and polymer characteristics as a function of reaction parameters, such as temperature, duration, and content of free trimethyl aluminum in the commercial MAO, was studied.

The polymerization of norbornene has been investigated in the presence of different bis(salicylaldiminate)nickel(II) precursors activated by methylaluminoxane. These systems are highly active in affording nonstereoregular vinyl-type polynorbornenes (PNBs) with high molecular weights. The productivity of the catalytic systems is strongly enhanced (up to 35,000 kg of PNB/mol of Ni × h) when electron-withdrawing nitro groups are introduced on the phenol moiety. On the contrary, the presence of bulky alkyl groups on the N-aryl moiety of the ligand does not substantially affect the activity or characteristics of the resulting PNBs. The catalytic performances are also markedly influenced by the reaction parameters, such as the nature of the solvent, the reaction time, and the monomer/Ni and Al/Ni molar ratios. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1514–1521, 2006

The selective oxidation of 5-hydroxymethyl-2-furaldehyde (HMF) to furan-2,5-dicarboxaldehyde (FDA) has been studied under different conditions, in terms of reaction temperature, oxidant agent (air, oxygen and their pressure), type of solvent (water, organic), in the presence of heterogeneous catalysts based on VOPO 4 ·2H 2 O (VOP). The attempt of obtaining in a one-pot reaction FDA from fructose passing through HMF as an intermediate product failed both in water and in a mixed water/methyl isobutyl ketone (MIBK) medium. The best performances in the direct oxidation of HMF to FDA have been obtained when VOP and N , N -dimethylformamide (DMF) were used as a heterogeneous catalyst and a reaction medium, respectively, under mild conditions (100 °C and room pressure of O 2 ). Productivity up to 8.13 mmol of FDA/(g catalyst h) was achieved with 95% selectivity at low HMF conversion. The modification of the heterogeneous catalysts, obtained by partial substitution of VO 3+ with different metal cations (Fe 3+ , Cr 3+ , Ga 3+ , Mg 2+ , Cu 2+ and Pd 2+ ), did not cause any improvement on the performances in this reaction.

Novel catalytic systems, prepared in situ by the oxidative addition of 8-hydroxyquinoline ligands to bis(1,5-cyclooctadiene)nickel(0) and activated by methylaluminoxane, were studied in ethylene polymerization. When 8-hydroxyquinoline was employed, only oligomeric products were obtained. On the contrary, 5,7-dinitro-8-hydroxyquinoline gave linear polyethylene (PE), but with a modest activity. For the catalyst based on 5-nitro-8-hydroxyquinoline, the productivity was largely dependent on the content of free trimethylaluminum (TMA) present in the commercial aluminoxane. The progressive optimization of the TMA/oligomeric methylaluminoxane ratio increased the productivity, which reached 700 kg of PE/(mol of Ni x h), by an order of magnitude.

New nickel (II) catalytic systems based on N,O chelate ligands, activated by methylaluminoxane, have been checked in the homopolymerization of methyl methacrylate (MMA) and its copolymerization with ethylene. In particular, the bis(8-hydroxy-5-nitro-quinolate)nickel(II)/methylaluminoxane system as well as the catalysts obtained by oxidative addition of either 8-hydroxy-5-nitro-quinoline or 8-hydroxy-5,7-dinitro-quinoline or 4-nitro-2-(p-nitrobenzylideneamino)-phenol to Ni(cod)2, subsequently activated by methylaluminoxane, have been employed. The influence of the reaction parameters on the catalytic activity and the characteristics of the resulting polymers has been investigated. All the obtained poly(methyl methacrylate) samples display a largely prevailing syndiotacticity degree, high molecular weights and a rather large polydispersity. The catalytic systems obtained through the oxidative procedure are able also to give copolymers of MMA with ethylene producing highly linear polyethylenes containing a low amount (1.5-2 mol %) of MMA counits, thus affording materials with improved surface properties.

The Guerbet self-condensation of n-butanol (BuOH) to 2-ethyl-1-hexanol (2EH) in the presence of different catalytic systems based on a metal hydrogenating/dehydrogenating component and a base was studied. In particular, homogeneous and heterogeneous palladium derivatives were used at 200 °C in combination with sodium butoxide (BuONa) as basic component. The effect of reaction parameters, such as BuONa concentration and amount of the metal component were investigated. Turnover numbers (TN) up to 80 mol of 2EH/(mol of Pd×h) were reached. In the case of heterogeneous palladium precursors an extensive leaching into solution was observed. The catalytic system based on completely heterogeneous copper chromite in combination with BuONa was also studied. In this case the effect of reaction parameters, such as the base concentration, the addition of either an ancillary base (MgO) or a dehydrating agent (CaO, molecular sieves) as well as reaction temperature was investigated. TN values up to 22 were obtained working at 280 °C. In all the experiments a complete selectivity to 2EH was ascertained, independently on the type of the adopted catalytic system and reaction conditions.

The synthesis of isobutanol ( i BuOH ) from methanol/ n -propanol (MeOH/PrOH) mixtures has been studied by the Guerbet reaction in the presence of either supported or homogeneous nickel-based/sodium methoxide (MeONa) catalytic systems. The catalysts performances were studied as a function of reaction parameters, such as pre-activation or not of the nickel component, temperature, MeONa/Ni molar ratio, gaseous atmosphere (H 2 or N 2 ) and the relative amount of the metal in the reacting alcohols mixture. In particular, PrOH conversions to i BuOH up to 75% were obtained when Ni/kieselguhr//MeONa system was employed. This system appeared more active than Ni/alumina//MeONa. Also homogeneous complexes of nickel such as nickel acetate tetrahydrate and nickel dichloro bis triisopropylphosphine, when combined with MeONa, displayed significant catalytic activity with turnover numbers (TN) up to about 66 mol of i BuOH /mol of Ni× h . In all cases the selectivity of the process to i BuOH was substantially complete. Also supported ruthenium and rhodium-based/MeONa catalytic systems were investigated. The results obtained indicated that all the investigated catalysts, when combined with MeONa, resulted active in the synthesis of i BuOH . The catalytic performances were improved when the metal component was employed without any pre-activation step, very low amount of metal component being sufficient to assure high productivity (turnover values up to about 150 mol of i BuOH /mol of Ru× h ).

The synthesis of isobutanol via the Guerbet condensation between methanol and ethanol was studied by using sodium methoxide (MeONa) as soluble basic component and copper-based catalysts as heterogeneous dehydrogenating/hydrogenating metal species. The effect of the nature of the catalyst and the relative amount of its individual components with respect to the reacting alcohols as well as of temperature on productivity and selectivity of the process was investigated. The collected data indicated that the copper chromite/MeONa was more active than Cu-Raney/MeONa system. The reaction was shown to proceed with the formation only of n-propanol and isobutanol. Ethanol conversion up to 61% with selectivity to isobutanol up to 98.4% was obtained. The same catalytic systems were also employed in the reaction of the methanol/ethanol/n-propanol ternary mixture. Again copper chromite/MeONa resulted more active than the Cu-Raney/MeONa system. Finally, experiments were carried out on methanol/n-propanol mixtures in the presence of the copper chromite/MeONa catalytic system by recycling both the recovered solid copper component and the liquid reaction mixture for evidencing eventual copper leaching by MeONa. On the basis of the obtained results it was concluded that in the Guerbet reaction copper chromite works as heterogeneous catalyst.

The homopolymerization of methyl methacrylate was investigated with bis(salicylaldiminate)nickel(II) complexes, such as bis[3,5-dinitro-N(2,6-diisopropylphenyl)salicylaldiminate]nickel(II) (IIIa) and bis[3,5-dinitro-N(phenyl)salicylaldiminate]nickel(II) (IIIb), and with methylaluminoxane (MAO) as an activator. In particular, the effect of the Al/Ni molar ratio on the catalytic activity and on the properties of the resulting poly(methyl methacrylate) (PMMA) was checked. The maximum activity was ascertained when an Al/Ni molar ratio equal to about 100 was used. However, the productivity of the catalytic systems was rather low. When the IIIa/MAO catalytic system was prepared under an ethylene atmosphere, an extremely high activity was observed, a productivity value of up to around 150,000 g of PMMA/(mol of Ni × h) being obtained, the highest ever found with nickel-based catalysts. No appreciable presence of ethylene counits in the polymeric products was also ascertained. When the IIIb/MAO system was used, similar results were found, and high molecular weight PMMAs were obtained, despite the absence of bulky isopropyl substituents in positions ortho and ortho′ to the N-aryl moiety of the salicylaldiminate ligand. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2117–2124, 2003

Salicylaldimine ligands, such as 5-nitro-N(2,6-diisopropylphenyl)salicylaldimine, 3,5-dinitro-N(2,6-diisopropylphenyl)salicylaldimine, and 3-phenyl-N(2,6-di-isopropylphenyl) salicylaldimine were checked in the oxidative addition to bis(1,5-cyclooctadiene)nickel(0) to prepare, after activation by methylaluminoxane (MAO), novel nickel-based catalytic systems active in the polymerization of methyl methacrylate. The catalytic behavior of the aforementioned systems, in terms of activity, molecular weight, and polydispersity of the resulting poly(methyl methacrylate) as well as its stereoregularity degree, was investigated as a function of the Al/Ni molar ratio, reaction temperature, and nature of the salicylaldimine ligand. The effect of ethylene atmosphere present during the preparation of the catalyst precursors was also investigated. The results are discussed and compared with those previously obtained by bis(salicylaldiminate)nickel(II)/MAO catalytic systems.

The reactivity of bis(salicylaldiminate)nickel(II) complexes ( I) with organoaluminum compounds under ethylene atmosphere, eventually in the presence of an ancillary phosphine ligand, has been studied by UV–VIS spectroscopy. When a large excess of methylaluminoxane (MAO) (Al/Ni molar ratio = 100) was used, in absence of phosphine ligands, the formation of an alkyl(monosalicylaldiminate)nickel(II) species absorbing at about 380 nm, active in the oligomerization of ethylene, was supposed to occur. Accordingly, when an equimolar I/phosphine mixture was treated with an excess of MAO (Al/Ni molar ratio = 100) an analogous absorption band was detected and the subsequent addition of an equivalent amount of Et3Al was supposed to cause the formation of the corresponding [alkyl(phosphino)monosalicylaldiminate)]nickel(II) species, as evidenced by 31 P-NMR analysis. The catalytic behavior of the homogeneous systems prepared in situ from I and different organoaluminum co-catalysts in the activation of ethylene was also investigated. In particular, the effect of reaction parameters, such as temperature and PC2H4 , as well as the type of salicylaldiminate ligand in the nickel precursor, the Al/Ni molar ratio and eventually the presence of a phosphine ancillary ligand, was studied. The catalysts evidenced very high activity with turnover frequencies (TOFs) up to 10 5 –10 7 h −1 , mainly oriented to the oligomerization rather than to the polymerization of ethylene. Changing the nature of I and reaction parameters it was possible to strongly modify the chemo- and regioselectivity of the catalytic process towards the formation of target olefin products, particularly 1-hexene. Depending on the type of I, minor amounts of polymeric products were also obtained. The heterogenization of the catalysts, either by precipitation in n-hexane of the reaction product from I and MAO, or by anchoring I to a SiO2-bound MAO, in order to increase the formation of polyethylene through a matrix effect, was also described. © 2002 Elsevier Science B.V. All rights reserved.

In the present paper, the dimerization of propylene to 2,3-dimethylbutenes (DMB) with fluorinated nickel precursors, such as bis(tetradecafluoro-4,6-nonandionate)nickel(II)·2dmf [Ni(tdfnd)2(dmf)2] and bis(hexafluoro-2,4-pentandionate)nickel(II) [Ni(hfacac)2], in combination with phosphine ligands and aluminium alkyl promoters, was investigated in fluorous solvents as reaction medium with the aim of realizing a catalytic process operating in a fluorinated biphasic system (FBS). The role of the nature of the perfluorinated medium was carefully examined and significant productivities (TOF up to ∼25,000 h−1) were ascertained. Also fluorinated phosphine ligands were used with the aim of improving catalyst solubility in the fluorinated phase. Finally, with the aim to reach the same goal, tris(pentafluorophenyl)borane [B(C6F5)3], was also employed in the place of organoaluminium co-catalysts. However, in all the catalytic experiments a progressive migration of the catalyst towards the hydrocarbon phase, generated by the formation of the oligomeric products, was observed, thus evidencing the difficulty of realizing a FBS olefin oligomerization catalytic process, at least under the adopted conditions.

The catalytic behaviour of novel α-nitroacetophenonate-nickel(II) complexes has been investigated as a function of reaction conditions, type and relative amount of the organoaluminium co-catalyst, as well as nature of the ancillary phosphine ligand, in order to orientate ethylene oligomerisation process towards specific target products. The reported data allowed to indicate that it is possible to shift the products distribution towards higher oligomers by increasing the Lewis acidity of the organoaluminium co-catalyst and by using a basic and bulky ancillary ligand such as tricyclohexylphosphine (PCy3). The catalyst productivity may be also readily modulated by choosing the proper organoaluminium co-catalyst and the suitable phosphine ancillary ligand. Under proper reaction conditions, a very high linearity (more than 80% of n-hexenes) of the C6 cut was obtained. On the other side, the mixture of the higher oligomeric components was found to have a relatively high degree of branching. This is likely due to the ability of the catalytic system to co-oligomerise ethylene with the produced dimeric and trimeric α-olefins, thus, affording more branched higher oligomers.

Novel catalytic systems based on bis-(chelate)nicke(II) precursors, such as bis (α-nitroacetophenonate)nickel(II) [Ni(naph) 2 ] and bis(2,6-diisopropyl―benzenesalicyladiminate)nickel(II) [Ni(dipbs) 2 ], and methylaluminoxane (MAO)= as the cocatalyst were employed for the polymerization of methyl methacrylate (NMA). Reaction paramethers were examined. Under proper conditions, the Ni(dipbs) 2 /MAo system allowed to obtain poly(MMA) with a very high productivity (TOF up to 70 000 h-1) and a remarkable syndiospecificity degree (rr > 80%) at room temperature without addition of an ancillary Lewis base.

The propylene dimerization to 2,3-dimethylbutenes (DMB) by homogeneous catalysts prepared in situ by an alternative method based on the reaction of bis(α-nitroacetophenonate)nickel(II) [Ni(naph) 2 ] with different organoaluminum compounds, in the presence of a bulky and basic alkyl phosphine such as tricyclohexylphosphine (PCy 3 ), was described. In particular, the influence of the nature of the organoaluminum co-catalyst as well as of the reaction temperature was studied. The catalysts prepared according to this procedure displayed higher activity at room temperature and in hydrocarbon medium as compared with those obtained by oxidative addition of α-nitroacetophenone to bis(1,5-cyclooctadiene)nickel(0) [Ni(cod) 2 ] in the presence of the same phosphine ancillary ligand, turnover frequencies up to 24 800 h −1 being achieved when methylalumoxane (MAO) was used as co-catalyst. Moreover, regio-selectivity values to DMB within the C 6 cut higher than 82% were observed under the above conditions. Finally, the regio-selectivity was scarcely influenced by decreasing the reaction temperature below 25°C, thus allowing to work at room temperature.

Novel nickel catalysts, prepared in situ by oxidative addition of α-nitroketones to nickel(0) complexes, in the presence of a phophine ancillary ligand and activated by organoaluminium co-catalysts were investigated in propylene oligomerization with the aim to selectively obtain 2,3-dimethylbutenes (DMB). In particular, the effect of the nature of the α-nitroketonate ligand as well as of the basicity and bulkiness of the phosphine on catalyst performances were studied. Finally, the influence of the type of organoaluminium co-catalyst and reaction temperature were examined. In particular, when the Ni(cod)2/tricyclohexylphosphine (PCy3)/α-nitroacetophenone (naph)/methylalumoxane (MAO) catalytic system was employed, the highest up to now reported regioselectivity within C6 cut (>90%) was achieved. Moreover, the use of balanced mixtures of MAO and Et2AlCl allowed to optimize the catalyst performances up to an overall yield to DMB of almost 70%, a significant productivity being also achieved (TOF=4500 h−1).

The propylene dimerization to 2,3-dimethylbutenes (DMB) by novel homogeneous catalysts prepared in situ by two alternative routes was described. The former synthetic procedure was based on the oxidative addition of hexafluoro-2,4-pentandione (hfacac) to bis(1,5-cyclooctadiene)nickel(0) [Ni(cod)2] in the presence of an ancillary phosphine ligand and an organoaluminium compound. The latter route consisted in the reaction of bis(perfluoroalkyl-β-diketonato)nickel(II) complexes with the organoaluminium compound in the presence of the phosphine ligand. In this context the novel bis(tetradecafluoro-4,6-nonandionato)nickel(II)·2 dimethylformamide complex [Ni(tdfnd)2(dmf)2] was synthesized and its crystal and molecular structures were determined. The catalytic systems obtained with both procedures resulted highly active in the oligomerization of propylene (TOF>20000 h−1). In particular, when Ni(hfacac)2 was combined with the bulky and basic tricyclohexylphosphine (PCy3) and MAO was adopted as co-catalyst a very high regioselectivity to DMB within the C6 cut was achieved (ca. 90%). The use of Ni(tdfnd)2(dmf)2 in the place of Ni(hfacac)2 gave similar results under the same reaction conditions. Changing the type of phosphine ligand and the nature of the organoaluminium co-catalyst it was possible to deeply modify both regio- and chemo-selectivity of the process, thus allowing to orientate the reaction towards specific target oligomeric products.

A novel approach for obtaining heterogenized catalysts, via oxidative addition of polymer-bound β-dithioacetylacetonate (sacsac) ligands to nickel(0) complexes was reported and their performances were investigated in the propylene oligomerization, in terms of activity and selectivity to 2,3-dimethylbutenes (DMB). In particular, the effect of the nature of the ancillary phosphine ligand as well as of the organoaluminium co-catalyst was studied. The influence of the addition to the reaction medium of chlorinated promoters was also checked. The results indicated that the catalysts prepared by this route were more active and selective towards DMB as compared with those previously prepared by an exchange reaction method. When basic alkyl phosphines, such as tricyclohexylphosphine (PCy 3 ) and triisopropylphosphine ( P i Pr 3 ), and organoaluminium co-catalysts with suitable Lewis acidity, such as Et 2 AlCl, were used, the resulting catalysts displayed a very high selectivity to DMB (∼80%) and an extremely high productivity (turnover frequency equal to 74,000 h −1 ), the latter being much higher as compared with that previously obtained with the homogeneous counterparts.

The oxidative addition of α-nitroacetophenone (naph) to bis(cyclooctadienyl)nickel(0) [Ni(cod) 2 ], in the presence or not of tricyclohexylphosphine (PCy 3 ) was proven to give the η 1 ,η 2 -cyclooctenyl)(naph)nickel(II) complex ( III ). When this reaction was carried out in the presence of PCy 3 , further addition of methylalumoxane (MAO) or trialkylaluminium compounds afforded the corresponding alkyl(PCy 3 )(naph)nickel(II) complex. This was also obtained by an alternative synthetic procedure involving the addition of a trialkylaluminium to the equimolar adduct of Ni(naph) 2 with PCy 3 . When the above complexes, independently of the synthetic procedure adopted, were generated in situ by using MAO as a co-catalyst (Al/Ni=100), they resulted in being active in ethylene oligomerization. Whereas in the absence of PCy 3 , they gave mainly linear C 4 –C 6 oligomers with turnover frequencies (TOFs) in the 4000–8000 h −1 range, the presence of the phosphine ancillary ligand not only produced a remarkable increase in activity (TOF=26,000–41,000 h −1 ) but also afforded a completely different distribution of oligomers, mainly branched C 6 –C 13 products being obtained.

Novel optically active monomers, based on different L-amino acid residues such as trans-(S)-4-(2-methacryloylamino-3-methylbutanoylamino)azobenzene and trans-(S)-4-( N-methacryloyl-2-pyrrolidinoylamino)azobenzene, have been prepared and homopolymerizd by free radical initiation. Circular dichroism spectra of the resulting polymers, as compared with those of the corresponding low molecular weight analogues, purposely synthesized, allow one to suggest that the macromolecules assume in solution achiral or chiral conformations with a prevailing screw sense, depending on the bulkiness and rigidity of the L-amino acid residue present in the side chains. The role of intra- and/or intermolecular hydrogen bonding between side-chain amido groups along the backbone and the structural requirements of the chiral groups in determining the macromolecular arrangement in also discussed.

The photochromic behaviour of optically active methacrylic polymers containing in the side chains a bulky chiral amino acid residue interposed between the backbone and the azobenzene chromophore through amido groups, such as poly [(S)-4-(2-methacryloylamino-4-methylpentanoylamino)azobenzene] [poly(MLEA)], poly[(S)-4-(2-methacryloylamino-3-methylbutanoylamino)azobenzene] [poly(MVA] and poly[(S)-4-(N-methyacryloyl-2-pyrrolidinoylamino)azobenzene] [poly(MPA)] was investigated in comparison with the corresponding low molecular weight model compounds. The photoresponsive properties of the above polymers were also evaluated by circular dichroism measurements at various extent of photoisomerization and in solvents with diferent polarity. All the results are discussed in terms of structural requirements of the macromolecules.

Halogeno(β-dithioacetylacetonato)nickel(II) complexes with different alkyl phosphine ligands have been studied in the selective propylene dimerization to 2,3-dimethylbutenes (DMB) in the presence of different organoaluminium compounds. When basic and bulky phosphine ligands, such as tricyclohexyl-(PCy3) and triisopropyl-phosphine ( P i Pr 3 ) were used in combination with suitable co-catalysts, such as Et3Al2Cl3, Et2AlCl and EtAlCl2/methylalumoxane (MAO), the best results in terms of productivity (up to ∼36,000 h−1) and yield to DMB (up to 68%) were obtained. A detailed analysis of the composition of C9 cut in some selected experiments allowed to evaluate the octane characteristics of the reaction mixture offering both interesting applicative perspectives and mechanistic information.

The nature of different acid sites on the surface of various niobium-based catalysts has been spectroscopically investigated by means of FT-IR and UV–VIS techniques. Surface acidity has been further characterized by acetonitrile adsorption and subsequent FT-IR analysis. The catalytic activity of the different examined samples has been preliminarily tested in the fructose dehydration to 5-hydroxymethyl-2-furaldehyde, a reaction of relevant industrial interest.

Pd(OAc) 2 undergoes easy and quantitative coordination to a cross-linked styrene/divinylbenzene resin functionalized with bis(diphenylphosphino)methane ligands to yield a supported palladium complex which behaves as a versatile and recyclable heterogenized catalyst for the hydrogenation of nitrocompounds and α,β-unsaturated aldehydes under mild conditions. Whereas nitrobenzene is converted only into aniline, cinnamaldehyde is selectively converted into hydrocinnamaldehyde.

Brominated and chloromethylated styrene–divinylbenzene resins were used for the synthesis of polymer-bound dithio-β-diketones, obtained by anchoring the chelate ligand through the central position. The heterogenized dithio-β-diketone ligand was subsequently reacted either as sodium salt with a Ni(II) phosphino derivative or directly with a Ni(0) complex in the presence of a free phosphine and activated in situ with an aluminum co-catalyst for the selective dimerization of propylene to 2,3-dimethylbutenes. The hetetogenized catalysts so obtained showed, particulary when prepared starting from chloromethylated styrene/divinylbenzene resins, very high activity and selectivity towards 2,3-dimethylbutenes. Moreover, the above catalysts, at least under the adopted reaction conditions, did not display any appreciable metal leaching during the catalytic cycle, thus working as really heterogeneous systems. Copyright © 1999 John Wiley & Sons, Ltd.

The telomerization of 1,3-butadiene with methanol in the presence of heterogenized palladium(II) catalysts, obtained by anchoring the metal on both a styrene/divinylbenzene macroporous resin and a linear poly(styrene) functionalized with bis(diphenylphosphino)methane moieties, is reported. In particular, the activity and selectivity to telomers of the above catalytic systems is compared with the corresponding homogeneous counterpart and with those previously obtained with analogous heterogenized systems via polymer-bound 1,3-bis(diphenylphosphino)propane moieties. The effect of a methoxide promoter is also studied. Finally, the performances and metal leaching in solution of the above heterogenized catalysts are checked after several reaction cycles in order to verify their real heterogeneous character.

The heterogenization of palladium complexes on silica as well as on functionalized styrene/divinylbenzene crosslinked resins and linear poly(styrene) is described. In particular, palladium (0) and palladium (II) derivatives were anchored to the above polymeric systems through their functionalization with bidentate ligands such as acetylacetonate and 1,3-bis(diphenylphosphino)propane moieties. The resulting heterogenized complexes were checked in the catalytic telomerization of 1,3-butadiene with methanol. Their performances were studied in terms of activity and selectivity to telomers. Whereas the heterogenization of palladium complexes either on silica or on polymer resins via the acetylacetonate ligand resulted labile during the catalytic cycle, the polymer-bound palladium complexes via the diphosphine ligand, when activated by an alkoxide, displayed activity and selectivity comparable with those of the corresponding homogeneous counterparts, without appreciable metal leaching in solution.

The oxidative polymerization of furan, 3-methylfuran and 2,2',5',2-terfuran, induced by iodine in organic solvents having different donicity, was investigated by time-resolved electron paramagnetic resonance (EPR) spectroscopy. The reaction was monitored starting from the onset of the process and radical species arising from the monomers in early stages of the polymerization reaction were detected. The comparison between experimental and theoretical hyperfine coupling constants, obtained by simulated EPR spectra and theoretical ab initio calculations, respectively, allowed one to structurally characterize the above radical species, thus enabling mechanistic conclusions about oxidative coupling. Moreover, the analysis of the time evolution of EPR spectrum during the oxidative polymerization process was used for evaluating the relative amount of localized and mobile radical species along the polymer backbone, thus getting preliminary information about conjugation extent and electroconducting properties of the final material.

The selective synthesis, by telomerization of 1,3-butadiene with alcohols in the presence of palladium catalysts, both of octadienyl ethers (especially from higher linear primary alcohols) and of butenyl ethers is reported. The variation of the alcohol/diene molar ratio plays a decisive role in both the cases, excess of alcohol favouring in the former case the synthesis of octadienyl ethers with respect to octatrienes, being useful in the latter case, together with other factors such as high P/Pd and low Pd/diene molar ratios, to favour the formation of butenyl ethers. It has in fact been discovered that, for palladium catalysts, the formation of butenyl ethers is ruled by a complex mechanism involving both the reversible formation of butenyl ethers and their direct transformation into octadienyl ethers.

Styrene–divinylbenzene resins were used for the synthesis of different polymer-bound β-diketones, obtained by anchoring the chelating group through either the central or the lateral position. The heterogenized diketone ligand was subsequently reacted with Ni(COD)2 analogously to the corresponding homogeneous catalysts active in α-olefin oligomerization. The heterogenized catalysts showed a good activity only when the central position of the chelate moiety was free. Heterogenization caused a significant change of selectivity: olefin oligomerization was accompanied by the formation of a large amount of polymeric products. This behavior is discussed in terms of steric effects caused by the bulky polymeric ligand. © 1998 John Wiley & Sons, Ltd.

The synthesis and structural characterization of a novel bidentate ligand such as bis(diphenylphosphino) methane bound to a cross-linked styrene/divinylbenzene resin and to linear poly(styrene) are reported. Moreover, the anchoring of palladium acetate to the above polymeric ligands is described and the structure of the heterogenized palladium(II) complexes obtained is proposed.

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.

Organometallic nickel complexes with bidentate P∩O chelating ligands of ylidic (C(O)HPPh3) and phosphino-acetic (CH(PPh2)COOH) 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.

The co-polymerization of ethylene with 1-hexene has been performed with titanium precursors based on carboxylato ligands in the presence of organoaluminium compounds as activators to afford linear low-density polyethylenes (LLDPEs). The influence of the polymerization parameters was studied with particular reference to the type and amount of catalyst components, solvent, temperature, ethylene pressure, 1-hexene concentration. The chloro-substituted bis-carboxylato titanium complex resulted the most active precursor in the co-polymerization, allowing to obtain copolymers with modulable composition in the 1–5 mol% range of 1-hexene units. The obtained copolymers were characterized by thermal analysis, X-ray diffraction spectroscopy, FTIR and NMR techniques.

Ethylene/1-hexene random copolymers with 1-hexene content in the range of 1-5 mol-%, synthesised in the presence of new heterogeneous catalyst systems based on bis-carboxylato and -bis-chloro-carboxylato titanium chelate complexes, have been characterised by FTIR microspectroscopy (FTIR-M), DSC calorimetry and X-ray scattering. The co-monomer content and sequence distribution in the various samples were determined by means of both FTIR-M and 13 C NMR spectroscopy. The deformation bands of methyl groups in the region of 1400-1330 cm -1 were used for the structural analysis of these copolymers. The effect of composition on the crystallinity and phase transitions of copolymers was analysed both in 1500-1 300 and 760-690 cm -1 1 frequency ranges as a function of the annealing temperature. A neat variation of the absorbance ratio of methyl band at 1378 cm -1 was recorded between 110 and 130°C corresponding to the melting range of the copolymer crystals. The crystallisation behaviour of the copolymers was examined by DSC in dynamic and isothermal conditions; the isothermal kinetics were analysed according to the Avrami model. A marked decrease in the bulk crystallisation rate, accompanied by changes in the nucleation and growth of crystals, was found with an increase in the co-monomer content. The melting behaviour of isothermally crystallised samples was also investigated and the melting temperatures of the copolymers at equilibrium conditions were related to the composition; the experimental data were consistent with the Flory exclusion model of side branches from the crystalline phase. The lowering of crystal growth rate in the copolymers has been accounted for by an increase in the free energy of formation of critical size nuclei due to the effect of the side branches.

The performances of ethylene polymerization catalysts based on III and commercial methylaluminoxane were investigated by reducing the content of free trimethylaluminum in methylaluminoxane by its reaction with 2,6-di-tert-butylphenol. This allowed optimization of the formulation of the catalyst, affording a high-molecular-weight linear polyethylene (PE) with a productivity [(1 900 kg of PE/(mol of Ni × h)], ten-fold higher than that previously achieved for the same system adopting commercial methylaluminoxane not pre-treated with the above phenol derivative.

The synthesis of isobutyl alcohol ( i BuOH) from methanol (MeOH) and n -propanol (PrOH) through the Guerbet condensation has been studied in batch experiments using bifunctional heterogeneous systems based on a dehydrogenating/hydrogenating metal (Pd, Rh, Ni or Cu) and a basic Mg–Al mixed oxide derived from hydrotalcite-type (HT) precursors. Only copper-based systems showed appreciable performances. In particular, the Cu/Mg/Al mixed oxides catalysts obtained by the co-precipitation method offered the best results in terms of activity and selectivity, thus allowing to reduce pollution problems connected with the up to now adopted copper chromite. These co-precipitated systems were also tested in some preliminary experiments carried out in gas–solid phase in a flow reactor, thus confirming promising application perspectives.

The homopolymerization of styrene by using different catalytic systems based on bis(salicylaldiminate)nickel(II) and methylaluminoxane was investigated. In particular, the effect on catalyst activity and polymer characteristics by electron withdrawing groups located on the phenolic moiety was studied. The influence of the bulkiness of the substituents on the N-aldimine ligand was also ascertained. Finally the catalytic performances were investigated as a function of the main reaction parameters, such as temperature, Al/Ni molar ratio and duration.

Vanadyl phosphate (VOP) was used as acid catalyst in the dehydration of fructose aqueous solutions to afford 5-hydroxymethyl-2-furaldehyde (HMF). Promising results, in terms of activity (turnover frequency (TOF) ≈ 200 mmol HMF/gcat h) and selectivity, have been achieved. New catalytic systems, obtained by substitution of some VO3+ groups with trivalent metals (Fe3+, Cr3+, Ga3+, Mn3+, Al3+), were also checked. In particular, when Fe-substituted VOP was employed the highest up to now reported activities were obtained working on concentrated fructose solutions in the presence of a low amount of catalyst (TOF up to 376). Notwithstanding the high concentration of the substrate in aqueous medium neither insoluble polymeric by-products nor HMF rehydration compounds were formed. Finally, preliminary experiments carried out with VOP catalysts supported on inorganic oxides allowed to conclude that this approach is promising, provided that a support with proper acid character is adopted.

The homopolymerization of ethylene by using different catalytic systems based on dinitro-substituted bis(salicylaldiminate)nickel(II) precursors such as bis[3,5-dinitro-N(2,6-diisopropylphenyl)]nickel(II) and bis[3,5-dinitro-N(phenyl)]nickel(II) in combination with organoaluminum compounds was investigated. In particular, the catalytic performances were studied as a function of the main reaction parameters, such as temperature, pressure, Al/Ni molar ratio, and duration. Methylaluminoxane resulted in the best co-catalyst. Activities up to 200 kg polyethylene/(mol Ni × h) to give a linear high-molecular-weight polymer were achieved. The influence of the bulkiness of the substituents on the N-aryl group of the aldimine ligand was also checked; it resulted in a determinant for catalytic activity rather than for polymer characteristics. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2534–2542, 2004

The synthesis of isobutyl alcohol ( i BuOH ) from methanol (MeOH) and n-propanol (PrOH) through the Guerbet condensation has been studied at 200 °C and under inert atmosphere (3.0 MPa of N2), using a two-component heterogeneous catalytic system based on pre-activated copper chromite and Mg–Al mixed oxides deriving from hydrotalcite-type (HT) precursors with different Mg/Al ratios. All the investigated catalysts displayed a significant activity, with an almost complete selectivity to i BuOH . Unlike the copper chromite/soluble sodium methoxide system, the catalysts were tolerant of the co-produced water and did not display any appreciable deactivation during the course of the reaction. The catalyst productivity was found to increase by reducing the Mg/Al ratio in the heterogeneous base, according to the increase of the fraction of medium–strong and strong basic sites which favour the aldol condensation between the aldehydes derived from MeOH and PrOH.

The catalytic synthesis of isobutanol ( i BuOH), via the Guerbet condensation of methanol with n-propanol is described.In particular, bifunctional catalysts based on either heterogeneous or homogeneous dehydrogenating/hydrogenating pal-ladium species and on sodium methoxide (MeONa) as basic component were investigated. When heterogeneous Pd/Cand MeONa was used as catalytic system a high activity was obtained with turnover numbers up to about 110mol of i BuOH/(mol of Pdh). The increase of the MeONa/Pd molar ratio increased the activity of the catalyst. However, differentlyfrom Cu-based/MeONa catalysts, a significant metal leaching was observed; recycle experiments indicated that both hetero-geneous and homogeneous palladium species are involved in the catalysis. When homogeneous palladium complexes, such astetrakis(triphenylphosphine)palladium(0) [Pd(PPh 3 ) 4 ], diphenylphosphinoethane(dichloro)palladium(II) [Pd(dppe)Cl 2 ] andbis(dibenzylideneacetone)palladium(0) [Pd(dba) 2 ], were used in combination with MeONa a remarkable activity was alsoobtained, independently of the oxidation state of the palladium precursor. During the reaction deposition of a solid was ob-served and recycle experiments carried out both on the recovered solid and on the liquid phase suggested that also in this casethe activity has to be addressed to both heterogeneous and homogeneous (or colloidal) palladium species.© 2003 Elsevier Science B.V. All rights reserved.

A new series of monochelate nickel(II) catalysts, obtained by oxidative addition of salicylaldimine ligands to bis(1,5-cyclooctadiene)nickel(0), was reported for the polymerization of ethylene (E). Almost stoichiometric amounts of MAO as co-catalyst were necessary in order to activate these systems, the productivity being dependent on the Al/Ni molar ratio. The activity and the average molecular weight of the resulting PE were mainly influenced by the nature of the substituents on both the phenolate moiety and on the N-aryl ring. In particular, when two nitro groups are present on the 3,5-positions of phenolate moiety high activity (up to 120,000 g PE/(mol Ni×h)) was observed. The obtained PE samples showed a high linearity and average molecular weight in the 100,000–500,000 Da range. The obtained results seem to suggest that, at least for these catalysts based on salicylaldiminate ligands, the presence of electron withdrawing nitro groups on the phenoxy moiety plays a more important role with respect to the bulkiness of the substituents on both the ortho positions of the N-aryl group in order to prevent chain transfer and thus enhance the molecular weight of the polymer.

Bis(salicylaldiminate)nickel(II) complexes, such as bis[N(2,6-diisopropylphenyl) salicylaldiminate]nickel(II) and bis(N-isopropylsalicylaldiminate)nickel(II), were activated by methylalumoxane (MAO) to give catalytic systems able to copolymerize ethylene (E) with methyl methacrylate (MMA), thus producing low molecular weight copolymers with a rather high content of MMA co-units (50- 80 mol-%). On the contrary, when catalytic systems, obtain- ed by oxidative addition of salicylaldimine ligands such as 5-nitro-N-(2,6-diisopropylphenyl)salicylaldimine (NPS) and 3,5-dinitro-N-(2,6-diisopropylphenyl)salicylaldimine (DNPS) to bis(cyclooctadienyl)nickel(0) [Ni(cod) 2 ], were activated with MAO, high viscometric average molecular weight (M v 10-30 × 10 4 Da) E/MMA copolymers with a low content of MMA co-units (3-6 mol-%) were formed, thus allowing to obtain directly by synthesis functionalized highly linear poly(ethylene)s (T m up to 130 °C) to be potentially applied as new materials with improved surface properties.

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 (∼20,000 Da) 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.

Novel Ziegler–Natta-type catalysts, prepared in situ by oxidative addition of carboxylic acids to bis(cyclooctadiene)nickel(0) [Ni(cod)2]/phosphine adducts and activated by different organoaluminum compounds, are described. These catalysts resulted very active in olefin oligomerization. When 2-nitrobenzoic acid (NBA), tricyclohexylphosphine (PCy3) and MAO were employed in combination with Ni(cod)2 for propylene oligomerization, a regioselectivity to 2,3-dimethylbutenes (DMB) within the C6 cut very close to 90% was achieved with a high productivity (turnover frequency (TOF) values up to 16,400 h−1). Similar results in terms of regioselectivity to DMB were obtained when trifluoroacetic acid (TFA) was adopted. However, although with a lower productivity, a higher value of overall yield to DMB (62.7%) was achieved. When these catalysts were used for ethylene oligomerization they resulted very active (TOF values up to 65,000 h−1), the nature of the phosphine ligand allowing to strongly affect the chemoselectivity of the process, shifting the oligomeric composition towards specific fractions.