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In this paper we compare two different reactions, aimed at the synthesis of 1,2-cyclohexanediol. Specifically: (a) the direct epoxidation and hydrolysis (dihydroxylation) of cyclohexene to trans -1,2-cyclohexanediol, with an aqueous solution of hydrogen peroxide, and (b) the hydrogenation of catechol to a mixture of cis and trans -1,2-cyclohexanediol, in an attempt to establish green protocols for the synthesis of diols. Both reactions, the dihydroxylation of cyclohexene and the hydrogenation of catechol, were carried out without organic solvents. In the former case, an unprecedented 97.4% yield to the glycol was obtained, by selecting proper reaction conditions and using a tungstic acid/phosphoric acid catalyst, in a biphasic system with a phase-transfer agent. In the second approach, a heterogeneous alumina-supported Ru(OH) x catalyst was used, and a 90% yield to the glycol was obtained. A comparison of the two processes allowed to show the lower environmental impact of the catechol hydrogenation route.

The surface acidic properties of niobium phosphate solid acidic catalyst (NbP) have been analyzed by FT IR spectroscopy before and after reactivity tests concerning the hydrolysis and dehydration to furfural of xylose, as model molecule, or of real corn stover hydrolysates. Nitriles adsorption over the fresh NbP catalyst evidences P OH and Nb OH groups acting as Bronsted acidic sites, whereas Nb5+ ions behave as Lewis exposed sites, showing medium strength acidity. The characterization of the used catalysts surface points out that, in spite of the strongly adsorbed surface species arising from the reactivity tests, both Lewis and Bronsted sites are still exposed, although slightly weaker in acidic strength and more heterogeneous than over the fresh catalyst. This effect can indeed explain the remarkably high reusability of this material, in terms of conversion and furfural yield. In situ IR studies of xylose conversion suggest that activation of xylose thorough coordination at Lewis sites is likely to occur in the reaction temperature range.

A novel catalytic system based on palladium supported on chitosan was synthesized adopting a MW-assisted process. This synthetic approach results efficient under mild reaction conditions and very short microwave irradiation times. The prepared catalyst was employed in the hydrogenation of ethyl cinnamate (EC) to ethyl hydrocinnamate (EHC) adopting both traditional heating and MW irradiation: this is the first study on this reaction which involves this type of catalyst. In addition, a one pot fully MW-assisted process which provides the synthesis of the Pd/chitosan catalyst and its direct use in the hydrogenation of ethyl cinnamate has been also studied. This one pot procedure assures fast reaction rate under mild reaction conditions avoiding the catalyst's isolation and purification, thus making easier the reaction scale-up. The achieved yields in the target product are particularly good and the system results completely recyclable, due to the stabilizing effect of the functionalized natural support toward the palladium particles.

International audience; Carbon nanotubes (CNTs) have been employed for the preparation of supported ruthenium nanoparticles using, for the first time, a low boiling alcohol or a mixture ethanol/water as solvent/reducing agent under microwave irradiation as heating source. These systems were employed as catalysts in the selective hydrogenation of p-chloronitrobenzene (p-CNB) to p-chloroaniline (p-CAN) and resulted efficient systems for the selective reduction of the nitro group in p-CNB under mild reaction conditions (60 °C and 4 MPa of H2), while the CCl bond remains intact, thus allowing the almost complete substrate conversion with total selectivity to the target product. These supported ruthenium nanoparticles are characterized by small average diameters and narrow particle size distributions, even if synthesized in the absence of any additional stabilizing agents and appear very promising systems also for other catalytic applications.

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.

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.

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 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).

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.

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.