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[PdX2(PPh3)2]/PPh3 (X = HCOO, AcO, NO3, Cl, TsO; X2 = SO4) and [Pd(AcO)2(dppf)] in HCOOH with 5% H2O catalyse the CO-ethene copolymerization to high molecular weight polyketones (2700–2900 gPK (gPd⋅h)−1 at 333 K, 4.5 MPa of CO/ethene 1/1; M ¯ n = 20000–40000 Da). Catalysis occurs in homogeneous phase because the PK is soluble in the reaction medium. The polydispersity M ¯ v / M ¯ n is close to 2 dL⋅g−1, as expected for a homogeneous process. With the dppf-based catalyst, when the copolymerization is carried out in water/formic acid = 60/40 (mol/mol), the PK precipitates during the copolymerization and the polydispersity rises to 3.16 dL⋅g−1, in line with a process that becomes heterogeneous.

The catalytic activity of a series of palladium diphosphine complexes of the type [PdX2(P∩P)] has been studied in the oxidative carbonylation of i-PrOH with p-benzoquinone as an oxidant. Diphosphine ligands have been chosen in order to cover a wide range of bite angles and electronic and steric parameters. Their properties have been correlated with the catalytic activity and selectivity of the reaction. The best catalytic performance has been achieved with weakly coordinating anions as well as non-bulky and electron-donating P∩P ligands with a relatively wide bite angle yet capable of maintaining a cis-coordination, such as cis-[Pd(OTs)2(pMeO-dppf)]. These results and those on the reactivity of dicarboalkoxy species of the type cis-[Pd(COOMe)2(P∩P)] toward reductive elimination, which is a crucial step in oxalate formation, suggest that the slow step of the catalysis depends on the nature of the P∩P ligand.

The catalytic system trans -[PdBr 2 (PPh 3 ) 2 ]/NEt 3 /PPh 3 /LiBr is highly active and selective in the oxidative carbonylation of i PrOH to the corresponding oxalate using benzoquinone (BQ) as a stoichiometric oxidant. The oxalate is formed together with minor amounts of carbonate and acetone. The influence of each component in the catalytic system is discussed together with the influence of the concentration of BQ, reaction time, temperature and CO pressure. NEt 3 neutralizes the acid released in the catalytic cycle, thus favouring the formation of a dicarboalkoxy intermediate. Added PPh 3 reacts with benzoquinone giving betaine, which is a base that contributes to a further enhancement of the catalytic activity. The Br − anion might coordinate the Pd(0) which is formed in the product forming step thus stabilizing it against decomposition and making its reoxidation easier and reentering into the catalytic cycle. The catalytic activity depends slightly only on the concentration of BQ, suggesting that either uncoordinated BQ is not involved in the slow step of the catalytic cycle or that BQ is strongly coordinated in these species. The catalytic activity toward oxalate increases upon increasing the concentrations of NEt 3 and PPh 3 , whereas the selectivity toward carbonate and the formation of acetone remains practically constant. The increase of the pressure of CO has a similar effect, except that the formation of acetone is suppressed. It is suggested that at relatively high pressure of CO, a pentacoordinated species may be formed so that there is no place for any interaction between palladium and the C–H bond before the β-H elimination. Instead there is a nucleophilic intrasphere attack of the alkoxy ligand onto a CO ligand. After catalysis the precursor trans -[PdBr 2 (PPh 3 ) 2 ] has been detected, together with trans -[PdBr(COO i Pr)(PPh 3 ) 2 ] and [Pd(BQ)(PPh 3 ) 2 ]. PPh 3 remains coordinated to the palladium centre during catalysis. A BQ- and halides-assisted catalytic cycle is proposed. In this cycle, the reoxidation occurs through the release of a proton from an ammonium salt or a phosphonium salt, which are formed during the catalysis, with reformation of the catalyst precursor.

The reactivity of the complexes cis -[Pd(OTs) 2 (PPh 3 ) 2 ] ( I ), trans -[Pd(COOMe)(OTs)(PPh 3 ) 2 ] ( II ) and trans -[(COOMe) 2 (PPh 3 ) 2 ] ( III ), regarding the catalytic oxidative carbonylation of MeOH to dimethyl oxalate (DMO) using benzoquinone (BQ) as a stoichiometric oxidant, has been studied in CD 2 Cl 2 /MeOH (10/1, v/v) by 1 H and 31 P{ 1 H} NMR spectroscopy. I reacts with CO and MeOH at 193 K giving II , which is transformed into III upon addition of a base. The same occurs in the presence of BQ. Instead, if the base is added before admission of CO, [Pd(BQ)(PPh 3 ) 2 ] is formed. Starting also from II , complex III is formed only after addition of a base. The base neutralizes TsOH which is formed in the transformation of I to II and III . III is unstable in the presence of 1 equivalent of TsOH and it is transformed into II . At 333 K, under 0.4 MPa of CO, III decomposes with formation of DMO and dimethyl carbonate (DMC) (15%) each), whereas, in the presence of BQ, III is unstable already at 298 K, with formation of only DMO (10%). Catalysis to DMO is observed at 333 K. Thus BQ enhances the reactivity of III and directs the catalysis selectively to DMO. I , II and III have also been used in catalytic experiments in pure MeOH at 298 K, under 0.3 MPa of CO. II and III are active even in the absence of a base (TOF ca . 30 h −1 ). I is active only after addition of a base. A catalytic cycle is proposed.

The reactivity of cis -[Pd(H 2 O) 2 (PPh 3 ) 2 ](TsO) 2 .2(H 2 O) ( I ,H 2 O), trans -[Pd(COEt)(TsO)(PPh 3 ) 2 ] ( II ) and trans -[Pd(COOMe)(TsO)(PPh 3 ) 2 ] ( III ) has been studied by 1 H and 31 P{ 1 H} NMR spectroscopy under conditions that mime the catalytic ethene hydromethoxycarbonylation (EHMC), i.e. in the presence of PPh 3 , H 2 O and TsOH. ( I ,H 2 O), in the presence of two equivalents of PPh 3 , reacts with MeOH and CO (0.3 MPa) at 193 K to give [Pd(COOMe)(TsO)(PPh 3 ) 3 ] ( III ′), which reacts with H 2 O in the presence of TsOH at 293 K to generate [PdH(PPh 3 ) 3 ](TsO) ( IV ) quantitatively. This hydride inserts ethene (0.3 MPa, 293 K) to give trans -[Pd(Et)(TsO)(PPh 3 ) 2 ] ( V ), which reacts with CO (0.3 MPa, 223 K) giving [Pd(COEt)(PPh 3 ) 3 ](TsO) ( II )′ and initiates the catalytic EHMC at 293 K. II , in combination with PPh 3 and TsOH, reacts at 293 K with MeOH with quantitative formation of methyl propanoate (MP) and IV and promotes the catalysis starting from this temperature, under 0.6 MPa of CO/ethene (1/1) when the ratio PPh 3 /TsOH/ II is 2/6/1; upon increasing the PPh 3 / II ratio, the catalytic activity passes through a maximum when the ratio is 4/1, even though it initiates at a higher temperature. In the absence of added ligand, MP is formed in a stoichiometric amount, catalysis is not observed and decomposition to Pd metal occurs. Therefore, PPh 3 is essential in order to stabilize hydride IV , though an excess of ligand is detrimental. III does not insert ethene even at 343 K, a temperature well above that at which catalysis is observed. All these experimental evidences support the Pd–H cycle.

The copolymerization of ethene with carbon monoxide catalyzed by [Pd(OAc)2(dppp)] in an aprotic solvent such as 1,4-dioxane or nitromethane is efficiently promoted both by H2O and HCOOH and yields a perfectly alternating polyketone (PK). The influence of the concentration of the promoters, pressure and temperature on the catalyst productivity and the limiting viscosity number (LVN) has been studied. The productivity increases with the increase of temperature and pressure. The LVN increases upon increasing the pressure and lowering the temperature. At 363 K and 9.0 MPa, in HCOOH/H2O/1-4,dioxane (2.7/1.35/1 molar ratio), the productivity is 37.50 kgPK (gPd h)−1 (LVN 2.77 dL g−1). LVN lowers upon increasing the concentration of the acid, suggesting that it is involved in the protonolysis chain-transfer process.

a b s t r a c t The reactivity of several phenols toward liquid phase alkylation with cyclohexene in the presence of heterogeneous and homogeneous acid catalyst at 358 K is studied. The comparison between Amberlyst 15 and CH3SO3H, as examples of heterogeneous and homogeneous systems, shows a higher activity of the former with different behavior of selectivity between the two systems, anyway, in both systems O-alkylation and ring alkylations occur. A remarkable difference in the selectivity of the ring alkylation between heterogeneous and homogeneous systems is observed: Amberlyst 15 shows a constant ortho/para ratio close to 2, while in the presence of CH3SO3H ortho/para is variable from 3 to 5, suggesting an involvement of the cyclohexyl phenyl ether rearrangement. This is proved also by a direct relationship between the ortho/para ratio and the concentration of the cyclohexyl phenyl ether when CH3SO3H is used as a catalyst. The formation of cyclohexyl aryl ethers is reversible; on the contrary, ring alkylation appears irreversible. The reactivity of the dimethylphenols shows a strong influence of the steric hindrance of the substituent on the electrophilic attack of the cyclohexyl cation, which is poorly influenced by the inductive effect of the methyl group. © 2011 Published by Elsevier B.V.

The selective hydrogenation of ethyl-benzoylacetate to 3-hydroxy-3-phenyl-propionate catalyzed by Pd/C in EtOH in a solution of KOH has been investigated. Mass transfers as well as adsorption and desorption stages do not influence reaction kinetics. A kinetic model is proposed based on the best fitting of the experimental data with Langmuir–Hinshelwood type kinetics equation. The mechanism implies that the enolate of the ethyl-benzoylacetate adsorbs strongly on two sites, thus occupying a large part of the surface Pd atoms without any reaction. The ethyl-benzoylacetate adsorbs also on two sites but with adsorption equilibrium constant almost three order of magnitude lower than that of the enolate anions. Also the hydrogen is poorly adsorbed, however, it forms Pd–H and reacts with the adsorbed keto-ester by a step hydrogenation mechanism in which the first hydride insertion is the rate-determining step. Furthermore, due to the low surface Pd–H availability and the fast desorption of the 3-hydroxy-3-phenyl-propionate the consecutive hydrogenolysis of the C–OH bond of the product is practically suppressed, thus achieving selectivity close to 100%.

An organic-inorganic hybrid material, PK-SiO2 (PK = polyketone), was employed as support for Pd catalysts. Their synthesis was carried out by MW irradiation of an ethanol solution of Pd(OAc)2 in the presence of the support. The obtained systems were characterized by solid state NMR, SEM, TEM, ICP, XPS, BET, gas porosimetry and tested in two probe reactions: the selective hydrogenation of cinnamaldehyde to hydrocinnamaldehyde carried out in decalin and the oxidation of 1-phenylethanol to acetophenone in water. For comparison, Pd/PK and Pd/SiO2 catalysts were also prepared by using the same procedure, characterized and tested in the same reactions. On the hybrid support the Pd nanoparticles resulted significantly smaller and with a more homogeneous size distribution compared to those on bare SiO2 or PK. The catalysts on the hybrid support allowed a higher performance and could be recycled up to five times without loss of activity and metal leaching. These results were related to the improved surface area of the hybrid material (compared to the low surface area of bare PK) ascribable to silica introduction, combined with the stabilizing effect of the polymeric counterpart against Pd nanoparticles agglomeration. © 2015 Elsevier B.V. All rights reserved.

[PdCl2(dppb)] is highly active in the catalytic CO-ethene copolymerization in H2O–H(CH2)nCOOH (n = 0, 1 or 2). The influence on the productivity, the limiting viscosity number and the average viscosity molecular weight M W ¯ v of the following reaction conditions is investigated: (i) solvent composition; (ii) temperature; (iii) CO and ethene partial pressure at a given pressure of one monomer; (iv) monomers ratio at a given total pressure; (v) total pressure at CO/ethene = 1/1; (vi) reaction time. The productivity passes through a maximum with a H2O molar fraction of 0.55–0.70 (14,800 gPK(g Pd h)−1 in H2O–HCOOH, H2O molar fraction = 0.58, 45 bar, CO/ethene = 1/1, 90 °C; LVN = 0.48 dLg−1, M W ¯ v = 21,194 Da). The productivity is in the order of the strength of the acid n = 0 > n = 1 > n = 2, whereas the activation energy is in the opposite order. These findings suggest that the protonation of the resting states β- and ɣ-chelate rings destabilizes them, thus favoring the chain-growing process. Proposed power rate laws fit the productivity data obtained at different monomer pressures. The productivity lowers with time, but in the first hour the rate remains almost constant. The morphology and crystallinity of selected PKs determined by solid state NMR is also discussed.

The title complex (I) has been isolated after running the hydro-methoxycarbonylation (HMC) of ethene (4.5 MPa of CO/C2H4 = 1/1, 343 K) in MeOH, catalyzed by [Pd(TsO)2(PPh3)2]. It has been characterized by IR, 1 H and 31 P NMR spectroscopy. Complex (I) reacts with MeOH, saturated with CO, even at r.t., yielding methylpropanoate (MP) in stoichiometric amount and Pd(0) complexes and/or trans-[Pd(COOCH3)(TsO)(PPh3)2] (II), the latter forms in the presence of PPh3 and of p-toluenesulfonic acid (TsOH); complex (I) catalyses the HMC of ethene to MP; it catalyses also the HMC of a different olefin yielding also a stoichiometric amount of MP. After catalysis, complex (I) is recovered as such or as [Pd(TsO)2(PPh3)2] (III), the latter forming when an excess of TsOH is used (Pd/TsOH = 1/8). Complex (II), a potential catalytic intermediate, has been prepared under conditions similar to those employed to synthesize complex (I), except for the presence of ethene. This complex, dissolved in MeOH saturated with C2H4, does not yield MP at r.t., whilst at 353 K, it becomes a catalyst precursor for the HMC of ethene, however, it is recovered as complex (I). The conversion of (II) to (I) occurs with CO2 evolution. For the conversion of (I) to (II), it is proposed that: (i) (I) reacts with MeOH yielding MP and a Pd(II)-hydride; (ii) this reacts with TsOH with hydrogen evolution and yielding complex (III); (iii) this reacts with CO and MeOH yielding (II). For the conversion of (II) to (I) it is proposed that: (i) (II) reacts with H2O yielding MeOH and a PdCOOH species; (ii) this evolves CO2 with formation of a Pd(II)-hydride; (iii) sequential addition of ethene and CO gives (I). In addition, it has also been found that catalysis is accompanied by formation of CO2 also when using complex (I) as catalyst and that the catalytic activity passes through a maximum with increasing the concentration of water (TOF=420 h−1 at 353 K, 4.5 MPa CO/C2H4 = 1/1, (I)/PPh3/TsOH = 1/6/8, H2O = 800 ppm). It is proposed that: (i) catalysis occurs through initial formation of a Pd(II)H species (which form after CO2 evolution from a Pd(COOH) species formed via interaction of H2O with CO), followed by the insertion of the olefin into the Pd(II)H bond to form a Pd(II)(alkyl) intermediate, which in turn inserts CO with formation of an acyl complex of type (I), which reacts with MeOH yielding the ester and Pd(II)H back to the catalytic cycle; (ii) a carbomethoxy complex of type (II) does not play a major direct role in the catalytic cycle; (iii) during the catalysis Pd(II)H consuming side reactions occur with formation of Pd(II) species of type (II) and/or (III); these species are reintroduced, as hydrides, back to the catalytic cycle via interaction with H2O and CO.

The complex [PdCl2(dppp)] catalyses the copolymerisation of CO–ethylene when employed in a mixture of methanol and water as solvent. In the absence of H2O, it is inactive and at the end of the experiment, formation of metallic palladium has been noted. A sharp increase in the activity occurs at a water concentration above 5%, to reach a maximum of 4100 g copolymer/(g Pd h) by increasing the content of H2O up to 20% (mol/mol). In AcOH as solvent the catalytic activity of [PdCl2(dppp)] is also strongly dependent on the content of H2O. In the absence of H2O it is inactive, though it does not decompose to palladium metal. Upon addition of H2O, it turns into a highly active system and the catalytic activity passes through a maximum of ca. 28 000 h−1 when the molar ratio H2O/AcOH=55%. The 13 C NMR spectra show that the polymer chain is perfectly alternated. Polyketones obtained in MeOH–H2O (molecular weight ca. 6.5×103 g/mol) are of three types, differing for the nature of end-groups H(CH2CH2CO)nOMe, MeOCO(CH2CH2CO)nOMe and H(CH2CH2CO)nCH2CH3. In AcOH–H2O, only one type of polyketone forms having ketonic end-groups (average molecular weight ca. 2.7×104 g/mol). On the basis of these experimental evidences, a mechanism for their formation is proposed. It is also proposed that the main role of H2O is that of forming an active Pd–H species which would start the catalysis upon interaction with CO through a reaction closely related to the water gas shift reaction (WGSR) (during the catalysis there is formation of CO2 in significant amounts). It is also proposed that the main role of acid is that of stabilizing Pd–H active species preventing their deprotonation to inactive species.

The hydroesterification of cyclohexene is catalyzed by a preformed Pd(PPh 3 ) 2 (TsO) 2 complex I in methanol as solvent. The effect of PPh 3 , TsOH, and water on the TOF has been evaluated. The system I /PPh 3 /TsOH=1/6/8, in the presence of 800 ppm of H 2 O, at 373 K and under 2.0 MPa of CO leads to a TOF as high as 850 h −1 . The increase of TOF observed adding a hydride source such as TsOH and H 2 O suggests that Pd-hydride species plays a key role in the first step of the catalytic cycle. The initial reaction rate increases linearly with the concentration of cyclohexene and of MeOH and passes through a maximum with increasing the pressure of CO. The rate equation r 0 = k 1 P CO (1+ k 2 P CO + k 3 P CO 2 ) −1 fits well the experimental data. The values of k 1 , k 2 , and k 3 have been evaluated at different temperatures. From the plot ln k versus 1/ T , E 1 =19.4 kcal/mol, E 2 =20.6 kcal/mol and E 3 =6.5 kcal/mol have been evaluated. On the basis of experimental evidences and of the kinetic study, a catalytic cycle mechanism has been proposed.

Polyketones are obtained by the copolymerization of carbon monoxide and ethylene in the presence of a palladium catalyst formed in situ from Pd(OAc) 2 , dppp and formic acid in methanol which acted as a solvent. The productivity (g polymer/g Pd * h) is significantly influenced by the concentration of formic acid. Using the ratio Pd/dppp/HCOOH=1/1/3000 at 90 °C and 45 atm, a productivity of 7500 h −1 is obtained. It is suggested that the efficiency of HCOOH as a promoter is due to its capability to act as a source of Pd-hydride species, which initiates the catalytic cycle.

The influence of some preparative variables, of the metal loading and of the support on the activity of Ru catalysts for the selective hydrogenation of benzene to cyclohexene has been studied. The reaction has been carried out in a tetraphase reactor (in the presence of an aqueous solution of ZnSO4) at 423 K and 5 MPa pressure. The effect of hydrogen diffusion on the reaction kinetics and on cyclohexene selectivity was studied. The hydrophilicity of the support was related to the observed selectivity. Hydrogen chemisorption indicates that the catalyst activity is not influenced by the Ru dispersion, but mainly by the weakly chemisorbed species on the catalyst surface.

This report describes a new class of “core–shell” electrocatalysts for oxygen reduction reaction (ORR) processes for application in Proton Exchange Membrane Fuel Cells (PEMFCs). The electrocatalysts are obtained by supporting a “shell” consisting of PtNix alloy nanoparticles embedded into a carbon nitride matrix (indicated as PtNix-CN) on a “core” of pyrolyzed polyketone nanoballs, labeled ‘STp’. STps are obtained by the sulfonation and pyrolysis of a precursor consisting of XC-72R carbon nanoparticles wrapped by polyketone (PK) fibers. The STps are extensively characterized in terms of the chemical composition, thermal stability, degree of graphitization and morphology. The “core–shell” ORR electrocatalysts are prepared by the pyrolysis of precursors obtained impregnating the STp “cores” with a zeolitic inorganic–organic polymer electrolyte (Z-IOPE) plastic material. The electrochemical performance of the electrocatalysts in the ORR is tested “in situ” by single fuel cell tests. The interplay between the chemical composition, the degree of graphitization of both PtNix-CN “shell” and STps “cores”, the morphology of the electrocatalysts and the fuel cell performance is elucidated. The most crucial preparation parameters for the optimization of the various features affecting the fuel cell performance of this promising class of ORR electrocatalysts are identified.

The interplay between morphology and electrochemical performance of a new class of “core–shell” electrocatalysts for the oxygen reduction reaction (ORR) is studied. The electrocatalysts, labelled PtNi–CNl Tf/STp, consist of a “core” of pyrolyzed polyketone nanoballs (indicated as STp “core” support) covered by a carbon nitride (CN) “shell” matrix embedding PtNix alloy NPs (indicated as PtNix-CN). The electrocatalysts are characterized by means of: (a) high-resolution transmission electron microscopy (HR-TEM); and (b) cyclic voltammetry with the thin-film rotating ring-disk electrode (CV-TF-RRDE) method. The structure of the STp “core” supports and the details of the preparation procedure, such as pyrolysis temperature, Tf, and treatment with H2O2, play a crucial role on modulating: (a) the morphology; and (b) the ORR performance of the electrocatalysts. In particular, the best results are achieved for PtNi–CNl Tf/STp systems: (a) including a STp “core” support with a high porosity; and (b) obtained at Tf = 600 °C. It is demonstrated that in general, the treatment with H2O2 of electrocatalysts is detrimental for the ORR performance. Nevertheless, in particular conditions, the treatment in H2O2 improves the ORR performance of PtNi-CNl Tf/STp. The results presented in this work allow to elucidate the complex correlation existing between: (a) the composition; (b) the interactions in PtNix-CN; (c) the morphology of STp and PtNi–CNl Tf/STp; and (d) the ORR performance of the electrocatalysts.

The kinetics of the copolymerization of ethylene with carbon monoxide has been studied in a batch slurry reactor using the homogeneous Pd complex [(dppp)Pd(H 2 O)(TsO)](TsO) as the catalyst precursor in methanol. The effects of the catalyst loading and the partial pressures of CO and ethylene on the rate of copolymerization have been studied over a temperature range of 353-373 K. The rate of copolymerization was found to increase with increasing catalyst loading and partial pressures of CO and ethylene. The approximate orders of reaction were found to be 0.63 and 0.72 with respect to dissolved CO and ethylene, respectively. Different rate equations based on probable reaction mechanisms were evaluated for fitting the rate data. The rate data were interpreted in terms of the activities of the monomers in solution instead of their concentrations. This is particularly important because the copolymerization involves the reaction of two gaseous monomers with significant differences in their solubilities and ideal behavior. The rate models were discriminated using statistical as well as thermodynamic criteria. A model derived by assuming the insertion of ethylene into the tetracoordinated Pd-acyl species as the rate-determining step has been found to represent the kinetics in good agreement with experimental results. The apparent energy of activation for copolymerization was found to be 49 kJ/mol.

The selective hydrogenation of benzene to cyclohexene in the presence of Ru supported catalysts has been investigated in a tetraphase slurry reactor at 423 K, at 5 MPa of pressure, in the presence of two liquid phases: benzene and an aqueous solution of ZnSO 4 (0.6 mol l −1 ). A study of the influence of the transport phenomena on the reactivity of the catalyst has been carried out. But no correlation between Carberry and Wheeler–Weisz numbers and the selectivity of the catalysts has been found. The main features of the catalysts are the strong dependence between the catalysts preparation procedure and their activity and selectivity. The best results have been observed with Ru/ZrO 2 catalysts. The influence of the bases employed in the precipitation of the catalysts precursor has also been investigated. KOH is the most effective, yield of 41% and initial selectivity of 80% of cyclohexene has been observed.

The mechanism of hydroesterification of styrene using in situ-formed Pd(OTs) 2 (PPh 3 ) 2 from Pd(OAc) 2 , PPh 3 and TsOH in methanol has been investigated by isolation and characterisation of catalytically active intermediates. From reaction mixtures, Pd–hydridocarbonyl and Pd–acyl complexes were isolated and characterised, based on which a Pd hydride mechanism has been proposed. Formation of palladium hydride species has also been confirmed by 31 P-NMR experiments.

The system Pd(OAc) 2 /BQ/Co(acac) 3 (BQ=benzoquinone), in combination with tetrabutylammonium bromide (TBAB) as a surfactant agent and a chelating ligand such as 2,9-dimethyl-1,10-phenanthroline (dmphen) or 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (dmdpphen), is an efficient catalyst for the oxidative carbonylation of phenol to diphenyl carbonate (DPC). The best results have been obtained using the system Pd(OAc) 2 /BQ/Co(acac) 3 /dmphen=1/30/8/5 (molar ratio) in which [Pd]=10 −3 mol l −1 and TBAB/Pd=60/1. This system gives the maximum productivity of 700 mol DPC/mol Pd h at 135°C and under P tot =60 atm (CO/O 2 =10/1 molar ratio). The role of each component of the catalytic system is discussed and a catalytic cycle is proposed.

The oxidative carbonylation of phenol to diphenyl carbonate is catalyzed by palladium salts in combination with a cocatalyst such as p -benzoquinone (BQ) or a salt of Co, Mn, Cu. The addition of a surfactant such as tetrabutylammonium bromide makes the catalytic system more efficient. The role of each component in the catalytic system is discussed. A catalytic cycle is proposed where, in the first step, diphenylcarbonate is formed from phenol and CO with concomitant reduction of Pd(II) to Pd(0) and formation of two protons. p -Benzoquinone, which is reduced to hydroquinone, in the presence of protons, reoxidizes Pd(0) to Pd(II) while the metal cocatalyst is reduced by hydroquinone which is reoxidized to p -benzoquinone. Oxygen and protons, arising from the last reaction, close the cycle with reoxidation of the reduced metal cocatalyst and formation of water.

Kinetics of carboxylation of styrene to methyl 2-phenylpropionate and methyl 3-phenylpropionate has been investigated using a homogeneous Pd(OAc)2/PPh3/p-toluenesulfonic acid catalyst system. The effect of concentration of styrene, catalyst, water, and partial pressure of CO on the activity, selectivity, and rate of reaction has been studied in a temperature range of 338−358 K. The activity of the catalyst as well as the selectivity of the products was sensitive to all the reaction parameters studied. The selectivity of 2-phenylpropionate was found to decrease substantially with an increase in temperature and was enhanced by an increase in the partial pressure of CO and beyond a styrene concentration of 3.84 kmol/m3. The rate of carboxylation varied linearly with the catalyst and was zero order with respect to styrene concentration in the range of 0.567−3.84 kmol/m3. An unusual trend of an increase in activity was observed beyond a styrene concentration of 3.84 kmol/m3. The rate also increased with an inc...

The hydrogenolysis of the c~-C-O bond of mandelic acid derivatives catalysed by 5% Pd/C, in the presence of hydrochloric or sulphuric acids as cocatalysts, was carried out in water or ethanol as solvent, under 35-150 kPa of hydrogen pressure, at 343 K. Typically, the substrate/catalyst/cocatalyst ratio was 200 : 1 : 10. The hydrogenation of the ethyl ester of mandelic acid in ethanol as solvent is much faster, ca. 20 times, than that of the acid in water. The influence of the concentration of the reagents, products and cocatalysts on the initial reaction rate was investigated. Upon increasing the concentration of the ester the rate increases to a plateau. The pressure of hydrogen has little influence. The products inhibit the reaction. The rate steeply increases and reaches a maximum upon increasing hydrochloric acid concentration. From equilibrium constant data, the concentration of protonated ester as a function of the hydrochloric cocatalyst concentration has been estimated. The trend of the concentration of the protonated species parallels the trend of the reaction rate, thus suggesting that the protonated species plays a key role in relation to the catalyst activity. It is suggested that from this species, adsorbed on the catalyst surface, a molecule of water is displaced by a hydride formed upon activation of molecular hydrogen by palladium. Though less effective than hydrochloric acid, sulphuric acid acts also as a cocatalyst. However, in the latter case, the initial hydrogenation rate increases to reach a plateau. In addition, when HC1 is introduced in the reaction after the preactivation step of the catalyst, the hydrogenolysis rate is equal to the rate observed when sulphuric acid is used as cocatalyst. It is suggested that in the first case the possible formation of the superficial PdOxCly may be related to the higher activity of the chlorided catalyst, i~ 1997 Elsevier Science B.V.

PdCl2(PPh3)2, in combination with an extra amount of PPh3, is an excellent catalyst precursor for the hydrodechlorination of α-chloroacetophenone to acetophenone by hydrogen transfer from the H2OCO system. The reaction occurs with concomitant evolution of CO2. Under typical reaction conditions (50–70°C, 40–80 atm, substrate/Pd/P = 2000/1/50, H2O/substrate = 8–12/1), the reaction occurs in 70–80% yield in 2 h, using ethanol or dioxane as a solvent ([Pd] = 5 · 10−4 mol · l−1). When the catalyst precursor is employed without adding an additional amount of PPh3 extensive decomposition to metallic palladium occurs. Also Pd C is active in promoting the hydrodechlorination reaction. As expected the reaction rate increases upon increasing concentration of catalyst, carbon monoxide pressure and temperature. The yield is slightly influenced by the concentration of the substrate. The effect of the concentration of H2O is the most significant. In ethanol as a solvent at low concentration of water the reaction rate increases to reach a plateau above 6–7 · 10−2 mol · l−1 of water. On the basis of the fact that it is known that (i) the precursor is reduced to a Pd(0) species by the H2OCO system, even in the presence of hydrochloric acid, which is freed during the course of the hydrodechlorination reaction and that (ii) the starting α-chloroacetophenone oxidatively adds to Pd(0) to give Pd(CH2COPh)Cl(PPh3)2 (I) and that (iii) this complex reacts with hydrochloric acid to give acetophenone and PdCl2(PPh3)2 (II), it is proposed that the hydrodechlorination reaction proceeds via the intermediacy of a species analogous to complex (I) and that (II) is reduced to the Pd(0) complex through the intercation of CO and H2O with the metal center to give a species having a Pd-(COOH) moiety, which after β-hydride abstraction gives a palladium-hydride species with concomitant evolution of CO2. The hydride gives off a proton and reduces Pd(II) returning a Pd(0) species back to the catalytic cycle. We found also that complex (I) is reduced to a Pd(0) complex with formation of acetophenone through the action of H2O and CO. It is proposed that this reaction, which may be at the base of a different catalytic path, occurs via the intermediacy of a species having a HPd(CH2COPh) which, after reductive elimination of acetophenone give the Pd(0) complex starting a new catalytic cycle. In the case of the Pd C catalyzed hydrodechlorination it is suggested that H2O and CO interacts on the surface of the metal to give a hydride and evolution of CO2 and that this hydride displaces a chloride anion from α-chloroacetophenone absorbed on the catalytic surface to give the hydrodechlorination product.

For the title copolymerization the catalyst productivity (g-polymer/g-Pd · h) is significantly influenced by the presence of water and of the acid as it passes through a maximum upon increasing concentration of H2O and of TsOH. In the presence of 450 ppm of H2O, the maximum productivity is ca. 3.7 times higher than when the copolymerization is carried out in the presence of 1% of trimethylorthoformate, used as H2O scavenger in MeOH as solvent, at 90°C, under 45 atm of total pressure, employing the catalyst precursor in the molar ratio Pd/dppp/TsOH 1/1/2 ([Pd] 5.6 × 10−5 mol · 1−1). Under similar conditions, but under 60 atm of the two monomers, in the presence of 900 ppm of H2O and when employing an excess of the acid ( TsOH Pd 6.4) the productivity reaches a maximum of ca. 11500 g-polymer/g-Pd · h, which is 1.4 times higher than that obtained when the TsOH Pd ratio is 2 1 . The promoting effect of H2O is ascribed to the possibility that a higher concentration of active PdH species, which are proposed to initiate the catalytic process through the insertion of the olefin into a PdH bond, is achieved through the interaction of carbon monoxide with water on the metal center, via a reaction closely related to the water gas shift reaction. It is also proposed that the promoting effect of the acid is due to the reactivation of inactive Pd(0) species, which inevitably form under the reducing reaction conditions, with formation of active PdH species. When the copolymerization is carried out in the presence of benzoquinone (BQ), either under the reaction conditions in which the productivity reaches a maximum or under unfavorable conditions, that is, in the presence of low or relatively high concentrations of water, the productivity has an average value of ca. 7000 g-polymer/g-Pd · h. Since it was found by other research groups that in the presence of BQ the polymer takes origin mainly through the insertion of CO into a PdOCH3 species whose formation is favored in the presence of BQ, the findings presented above give further support to the suggestion that the promoting effect of H2O and of TsOH are due to the possibility that, when present in appropriate amounts, they favour the formation of PdH species which start the catalytic cycle.

The title complex was prepared by reacting Pd(AcO) 2 first with dppp and then with TsOH·H 2 O in MeOH at r.t. It is highly active in COC 2 H 4 copolymerization in MeOH. It has been characterized by IR and 1 H and 31 P NMR spectroscopies. The X-ray structure consists of a packing of monomeric palladium cations and tosylate anions in the ratio 1:1. The palladium atom is in rather distorted square coordination.

The alternating copolymerization of carbon monoxide with ethene is efficiently accomplished using [PdCl2(dppf)] as catalyst precursor in H2O–HCOOH as a solvent. At 90 °C, under 4.5 MPa of total pressure with the monomers in the ratio 1/1, the productivity passes through a maximum of 18,100 gPK(gPd h)−1, when the concentration of H2O is 50 mol.%, in which case the limiting viscosity number of the polyketone is 0.51 dL g−1. A much higher LVN is obtainable at a lower temperature. A satisfactory balance between productivity and LVN is achievable under higher pressure (10,100 gPK(gPd h)−1, LVN = 6.5 dL g−1 under 9.0 MPa, CO/ethene = 1/1, at 45 °C, H2O 40 mol.%). The influence of the operative conditions on productivity and LVN is discussed. The kinetics under different pressure of CO, keeping constant that of ethene, and the kinetics under constant total pressure at different CO/ethene ratios show that the copolymerization rates are virtually constant with time within 1 h reaction. The PK presents only keto-end groups ( COCH2CH3) and catalysis occurs with the concomitant evolution of CO2. NMR evidences show that the chloride-precursor is transformed, through the interaction of H2O with CO on the metal center, into a Pd-hydride species that starts the catalysis. A catalytic cycle is proposed.

The complexes [Pd(COOMe)nX2−n(PPh3)2] (n = 0, 1, 2; X = TsO, OAc, ONO2, Cl, Br), [Pd(SO4)(PPh3)2], [PdCl2(PPh3)]2 and PdX2 (X = Cl, Br, I) catalyze the oxidative ethene carbonylation in MeOH using benzoquinone (BQ) as stoichiometric oxidant. The main products dimethyl succinate (DMS) and dimethyl oxalate (DMO) are formed together with minor amounts of methyl propanoate and dimethyl carbonate. The formation of DMS unambiguously proves that ethene inserts into a Pd–COOMe bond. The influence of the CO/ethene ratio at constant total pressure and of the BQ/Pd ratio on the product distribution has been studied. Model reactions of a Pd-hydride with BQ, of trans-[Pd(COOMe)(TsO)(PPh3)2] with ethene in the presence of BQ and of trans-[Pd(COOMe)2(PPh3)2] with BQ have been studied by 31P{1H} NMR. BQ consumes the Pd–hydride and directs the catalysis toward a Pd–COOMe initiator leading to DMS. In the catalysis to DMO, BQ is likely to favour the formation of a Pd–(COOMe)2 species having the two carbomethoxy ligands in vicinal position such to favour the elimination of the product. The proposed catalytic cycles for the formation of the products are discussed.

bis(alkoxycarbonyl) complexes of platinum of the type [Pt(COOR)2L] [L = 1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp), l,4-bis(diphenylphosphino)butane (dppb), 1,1'-bis(diphenylphosphino)ferrocene (dppf) or 1,2-bis-(diphenylphosphino)benzene (dpb); R = CH3, C6H5 or C2H5] were obtained by reaction of [PtCl2L] with carbon monoxide and alkoxides. Palladium and nickel complexes gave only carbonyl complexes of the type [M(CO)L] or [M(CO)2L]. The new complexes were characterized by chemical and spectroscopic means. The X-ray structure of [Pt(COOCH3)2(dppf] · CH3OH is also reported. The reactivity of some alkoxycarbonyl complexes was also investigated.

Unexpected corrosion problems that arose in a crystallization plant with evaporators made entirely of type 316L (UNS S31603) stainless steel (SS) were solved using a corrosion inhibitor system of ethylenediaminetetraacetic acid (EDTA)-hydroxylamine sulfate (Sl)-iron anions (Fe2+). An experimental statistical plan reduced the number of experiments needed to optimize the concentration of EDTA-Sl-Fe2+. Moreover, the plan allowed more rapid and economical study of the action of each component in the inhibition mechanism. Statistical processing of the data collected from the potential-vs-time, anodic, and cathodic potentiodynamic measurements permitted estimations of the influence of each independent variable (EDTA, Sl, and Fe2+concentrations). Voltammetric, polarographic, anodic potentiodynamic curves, and Flade potential measurements helped further understanding of the inhibiting system.

An experimental statistical plan is utilized to solve corrosion problems of a section of an industrial plant for the production of caprolactam, consisting of a multistage flash evaporator entirely constructed in AISI 316L (X2CrNiMo 17 12 2). Preliminary tests show that the nitrates or acidity due to the sulfuric acid do not influence the corrosive phenomena and confirmed the positive, though costly, effect of adding hydroxylamine sulfate (SI) in the evaporator feed. An experimental plan was prepared to diminish the cost and dosage of SI in the system: the experimental statistical approach has allowed us to minimize the number of tests required in order to define the system rapidly and adequately, and to optimize the required amount of SI. The data processed have been obtained in a two-step experimental plan that allowed us to establish a relationship between the logarithm of critical corrosion current (icr) and the concentrations of some evaporator feeding components. In addition, it has been possible to clarify certain corrosion effects and to reduce the SI addition up to 1.4 g/l, thereby optimizing the chemical system and considerably reducing maintenance costs. A plausible explanation of the related effects of some of the feeding components is also proposed. Korrosionsinhibierung in einer industriellen Kristallisationsanlage: Verfahrensoptimierung mittels Statistik Die vorliegende Arbeit handelt von einer experimentellen statistischen Vorgehensweise zur Losung von Korrosionsproblemen in einer industriellen Anlage. Die Anlage, die den Produktionszyklus fur Caprolactam abschliest, besteht aus einem mehrstufigen Entspannungsverdampfer, der ausschlieslich aus AISI 316L (X2CrNiMo 17 12 2) gefertigt ist. Vorversuche haben ergeben, das die Nitrate Oder der durch Schwefelsaure bedingte Sauregehalt keinen Einflus auf die Korrosion haben und bestatigten die vorteilhafte, wenn auch kostspielige Wirkung der Zugabe von Hydroxilamin sulfat (SI) in die Versorgungsleitungen des Verdampfers. Zur Senkung der Kosten und zur Verringerung der SI-Zugabe wurde eine experimentelle Versuchsreihe ausgearbeitet, deren statistische Behandlung es ermoglichte, mit einer minimalen Anzahl von Versuchen das System schnell und ausreichend einzustellen und die erforderliche SI-Menge zu optimieren. Die Auswertung der Daten aus zwei aufeinanderfolgenden Versuchsreihen zeigte einen Zusammenhang zwischen dem Logarithmus des kritischen Korrosionsstroms (icr) und der Zusammensetzung einiger Komponenten in der Versorgung der Verdampfer. Diese Beziehung ermoglichte die Klarung einiger Korrosionsvorgange und die Verminderung der SI-Zugabe bis auf 1,4 g/l, wodurch das chemische System optimiert und die Instandhaltungskosten erheblich gesenkt werden konnten. Es wurde auch versucht, eine plausible Erklarung fur die damit verbundenen Effekte einiger der Speisekomponenten zu geben.

The carbonylation of (η3-allyl)palladium(II) chloride dimer in the presence of an excess of ylide, such as Ph3PC(H)COR (R = Me or Ph) (Pd:ylide = 1:5) in MeOH or EtOH, at a CO pressure of 4 atm at room temperature occurs with reduction of the palladium(II) complex to palladium metal and with formation of the corresponding alkyl 3- butenoate with a high yield. The ylide does not give rise to any carbonylation product. When the carbonylation is carried out in the presence of PPh3 (Pd : PPh3 = 1 : 2–3), there is also formation of the unsaturated ester, although in lesser amount, together with [Pd3(PPh3)n(CO)3] (n = 3 or 4) or [Pd(PPh3)3(CO)] andtrans-[Pd(PPh3)2(COOR)Cl] (R = Me or Et). These products also form when the carbonylation is carried out in the presence of NEt3 or PrCOONa, in place of the ylide, and of PPh3. It has also been found that [Pd(PPh3)2Cl2] reacts in MeOH or EtOH at a CO pressure of 4 atm at ambient temperature in the presence of an excess of ylide to give the corresponding carbalkoxy complextrans-[Pd(PPh3)2(COOR)Cl]. These findings suggest that the ylide probably promotes formation of carbalkoxy species, as do NEt3 or PrCOONa because the ylide can behave as a base (pKa ⋍7). They are strong support for the suggestion that the carbonylation of (allyl)palladium complexes occurs via a (carbalkoxy)palladium species.

The acyl complex trans -[Pt(PPh 3 ) 2 (CO n Bu)Cl] ( A ) has been synthesized by reaction of [Pt(PPh 3 ) 2 Cl 2 ] with 1-butene under 100 atm of CO at 80–100°C, in ethanol. With 2-butene rather than 1-butene under the same conditions, a mixture of the above acyl complex and of trans - [Pt(PPh 3 ) 2 (CO s Bu)Cl] ( B ) was formed. Complexes A and B do not interconvert. The new acyl complexes A and B have been characterized by IR and 1 H NMR and 13 C NMR spectroscopy. The ratio A / B increases with PPh 3 /Pt ratio and with temperature. The formation of two isomers when 2-butene is used involves an isomerization process which is likely to be limited to the alkyl precursor complexes. The reactivity of complexes A and B has been tested in reactions with SnCl 2 , H 2 , HCl and trans -[Pt(PPh 3 ) 2 HCl]. From the reaction solutions crystals of cis -[Pt(PPh 3 ) 2 Cl(SnCl 3 )] have been obtained. Its molecular structure has been determined by X-ray diffraction. The Pt atom has cis square planar coordination, with angular distortions due to steric factors. The strong trans influence of the SnCl 3 group is confirmed by the lengthening of the trans Pt-P distance. The SnCl 3 group has the pyramidal geometry found in all related compounds.

This report describes a new family of bimetal carbon nitride (CN) electrocatalysts for the oxygen reduction reaction (ORR) for application in polymer electrolyte membrane fuel cells (PEMFCs). The materials, which bear active sites based on Pt and Rh, are prepared with a three-step protocol consisting of: (1) the synthesis of a homogeneous zeolitic inorganic–organic polymer electrolyte (Z-IOPE) precursor; (2) the pyrolysis of the precursor at a temperature Tf = 400, 500, 600, 700 or 900 °C; (3) the activation, yielding the final product. It is found that Tf has a major effect on the structure and the electrochemical properties of these electrocatalysts, as determined from a wide array of independent characterization techniques including: high-resolution thermogravimetry (HR-TGA); Fourier-transform medium infrared (FT-MIR), Fourier-transform far infrared (FT-FIR) and confocal micro-Raman spectroscopies; powder X-ray diffraction (powder XRD); X-ray photoelectron spectroscopy (XPS); and electrochemical investigations carried out with the cyclic voltammetry thin-film rotating disk electrode (CV-TF-RDE) method. All the information is integrated to propose a comprehensive model correlating the effect of Tf on the structure of the materials with the corresponding electrochemical performance. The best results in the ORR are obtained with materials prepared at 600 ≤ Tf ≤ 700 °C. These systems present the optimal compromise between the size of the metal-rich nanoparticles, the degree of graphitization of the carbon nitride support and the concentration of ligands blocking the active sites. The best Pt-Rh electrocatalysts exhibit an ORR activity very similar to the Pt/C reference. In addition, the peculiar structure of the proposed materials, which are characterized by active sites supported on the carbon nitride bulky materials, results in a better tolerance toward typical contaminants in the ORR process such as chloride anions with respect to the Pt/C reference.

The catalytic system Pd/C—HCl is highly active in the reduction of mandelic acid derivatives to phenylacetic acid derivatives with carbon monoxide when the aromatic ring is para-substituted with a hydroxy group. Typical reaction conditions are: 70–110 °C, 20–100 atm of carbon monoxide, benzene—ethanol as reaction medium, substrate/Pd=102–104/1, HCl/substrate=0.3–0.8/1. [Pd] = 10−2 −10−4 M. When the catalytic system is used in combination with PPh3 a slightly higher activity is observed. Comparable results are observed when using a Pd(II) catalyst precursor such as PdX2, in combination with PPh3, or PdX2(PPh3)2 (XCl, AcO). When operating at 110 °C, decomposition to metallic palladium occurs. Pd(II) complexes with diphosphine ligands, such as diphenylphosphinemethane, -ethane, -propane or -butane, do not show any catalytic activity and are recovered unchanged. These observations suggest that Pd(0) complexes play a key role in the catalytic cycle. The proposed catalytic cycle proceeds as follows: the chloride ArCHClCOOR, formed in situ upon reaction of ArCHOHCOOR with hydrochloric acid, oxidatively adds to a Pd(0) species with formation of a catalytic intermediate having a Pd—[CH(Ar)COOR] moiety, which inserts a CO molecule, yielding an acyl intermediate of the type Pd—[COCH(Ar)COOR]. The nucleophilic attack of H2O on the carbon atom of the carbonyl ligand gives back the Pd(0) complex to the catalytic cycle and yields a phenylmalonic acid derivative, which produces the final product, ArCH2COOR, upon CO2 evolution. Alternatively, protonolysis of the intermediate having a Pd—[CH(Ar)COOR] moiety yields directly the final product and a Pd(II) species, which is then reduced by CO to Pd(0). Moreover, no catalytic activity is observed when the Pd/C—HCl system is used in combination with any one of the above diphosphine ligands, probably because these ligands block the sites on the catalyst able to promote the catalytic cycle or because they prevent the reduction of Pd(II) to Pd(0). The influence of the following reaction parameters has been studied: concentration of HCl, PPh3, palladium and substrate, pressure of carbon monoxide, the temperature, reaction time and solvent. The results are compared with those obtained in the carbonylation of aromatic aldehydes to phenylacetic acid derivatives catalyzed by the same system, for which it has been proposed that the catalysis occurs via carbonylation of the aldehyde to a mandelic acid derivative as an intermediate, which is further reduced with CO to yield the final product.

Benzyl alcohols are carbonylated to phenylacetic acid derivatives in the presence of a palladium catalyst. Typical reaction conditions are: temperature 9O–120°C;P(CO)=20–80 atm; benzyl alcohol/ROH/Pd=100–200/300–1000/1; [Pd]=0.5×10−2−1 × 1O−2 M; solvent: dioxane, benzene, ethanol; reaction time 1–4 h. Under these experimental conditions high yields are obtained only when the aromatic ring contains a hydroxy substituent at the para position and when the palladium precursor is a chloride used in combination with 2–4 equivalents of PPh3. When the substituent is in a m- or o-position or is a methoxy group, or in the case of benzyl alcohol, only trace amounts of phenylacetic acid derivatives are obtained. The system PdY2(PPh3)2-PPh3 yields the same results as PdY2 with equivalent amounts of phosphine (Y=Cl, Br, I, CH3COO). When the precursor is employed in combination with a base, catalysis does not occur to an appreciable extent. On the contrary, when HCl is added in an amount comparable to that of the palladium precursor (HCl/Pd=2–15), slightly higher yields are obtained. These results suggest that the starting benzyl alcohol reacts with HCl to yield the corresponding chloride, which initiates the catalytic cycle. Moreover, it has been observed that the best results are obtained when the palladium(II) precursor decomposes to metallic palladium. Pd/C is also active, provided that it is employed in combination with HCl and PPh3. Thus, for example, the system Pd/C-HCl-PPh3 is catalytically equivalent to the system that originates from the initial precursor PdCl2(PPh3)-PPh3, eventually in the presence of added HCl. Low catalytic activity is observed in the absence of PPh3 or when this ligand is added in relatively small amounts. The highest yields are obtained when P/Pd=2–3. These facts suggest that the PPh3 ligand eases the oxidative addition step by enhancing the electron density on the metal. Under these conditions, the yield increases with increasing gas pressure. When the ligand is present in relatively large excess, the catalytic activity drops dramatically, probably because PPh3 competes with the coordination to the metal. The catalytic activity is strongly influenced by the nature of the solvent. The yield decreases in the order: dioxane » ethanol ≈ benzene, and depends also on the ROH/solvent ratio; the highest yields are achieved when the EtOH/dioxane ratio is ca. 1/5 (ml). At higher concentrations of EtOH the yield is significantly lower, probably because the equilibrium between benzyl alcohol and hydrochloric acid is less favorable to the formation to benzyl chloride and/or the acid competes with the chloride for the oxidative addition to the metal. A mechanism for the catalytic cycle is proposed: (i) oxidative addition of ArCH2Cl to ‘reduced palladium’, which may be palladium coordinated by other palladium atoms, and/or carbon monoxide, and/or phosphine ligands. (ii) Carbon monoxide ‘insertion’ into Pd—benzyl intermediate with formation of an acyl intermediate. (iii) Nucleophilic attack of EtOH on the carbon atom of the acyl intermediate to give the desired product and return the catalyst back to the catalytic cycle. The promoting effect of the hydroxy substituent in the para position is interpreted in terms of resonance structures, in which deprotonation of this substituent may play an important role in weakening the CCl bond, thus easing the initial step of the catalysis.

cis-[Pd(ONO(2))(2)(PPh(3))(2)] (1) reacts under mild conditions with CO in methanol (MeOH) in the presence of pyridine (py), yielding trans-[Pd(COOMe)(ONO(2))(PPh(3))(2)] (1a). The use of NEt(3) instead of py leads to a mixture of 1a, trans-[Pd(COOMe)(2)(PPh(3))(2)] (2), and [Pd(CO)(PPh(3))(3)]. Pure 2 was prepared by reacting cis-[Pd(OTs)(2)(PPh(3))(2)] with CO in MeOH and subsequently adding NEt(3). The nitro complex trans-[Pd(COOMe)(NO(2))(PPh(3))(2)] (3a) was prepared by reacting trans-[Pd(COOMe)Cl(PPh(3))(2)] with AgNO(2) or with AgOTs and NaNO(2). New syntheses for 1 and trans-[Pd(NO(2))(2)(PPh(3))(2)] (3) are also reported. All complexes have been characterized by IR and (1)H and (31)P{(1)H} NMR spectroscopies. Complexes 1 and 2 exchange irreversibly and quantitatively one nitrato with one carbomethoxy ligand, yielding 1a. 2 in CD(2)Cl(2) at 40 degrees C decomposes with the formation of dimethyl carbonate (DMC), whereas under 4 atm of CO, DMC and dimethyl oxalate (DMO) are formed, ca. 12% each; in the presence of PPh(3) and in the absence of CO, decomposition occurs at 60 degrees C with the formation of DMC only, suggesting that decarbonylation involves a five-coordinate intermediate or predissociation of a PPh(3) ligand. The oxidative carbonylation of MeOH does not occur when using NaNO(2) or NaNO(3) as the oxidant and 1, 1a, 3, or 3a as the catalyst precursor. On the contrary, when using benzoquinone (BQ) as the oxidant, these complexes, 2, or [Pd(COOMe)(2-n)X(n)(PPh(3))(2)] (X = Cl, OAc, OTs; n = 1, 2) promote selective catalysis to DMO. After catalysis the precursors are transformed into [Pd(BQ)(PPh(3))(2)](2).H(2)BQ, [Pd(CO)(PPh(3))](3) and [Pd(CO)(PPh(3))(3)]. Also the last with BQ gives selective catalysis to DMO. The solid-state structures of 1.CH(2)Cl(2) and 1a have been determined by means of single-crystal X-ray diffraction.

The [PdCl2(dppf)] complex efficiently catalyzes the terpolymerization of propene and ethene with carbon monoxide in HCOOH–H2O as a solvent, when H2O concentration ranges between 50 and 65 molar %. The productivity, the melting temperature and the viscosity average molecular weight of the terpolymer depend on the propene concentration and on the reaction time. The NMR analysis of the polymer composition indicates the presence along the chain mainly of ethene–CO units together with a low percent of propene–CO units. A reaction mechanism is proposed and discussed.

The influence on the productivity of [PdCl2(dapp)] in H2O–CH3COOH in the CO–ethene copolymerization and on the LVN of the copolymer of the following reaction parameters has been studied: (i) composition of the H2O–CH3COOH reaction medium; (ii) temperature; (iii) CO/ethene ratio at a given total pressure; (iv) total pressure at fixed ratio CO/ethene = 1/1; (v) CO or ethene partial pressure at a given pressure of one monomer; (vi) reaction time. High molecular weight PKs are obtained under high pressure with the monomers in the ratio 1/1 at relatively low temperature and with a H2O/CH3COOH 40–50% with productivity ranging from 4 to 20 kg PK(g Pd h)−1. The relation between productivity and LVN has been discussed in the light of the key steps of the catalytic cycle.

The neutral precursor cis -[Pd(SO 4 )(PPh 3 ) 2 ] turns into an active catalyst for the hydromethoxycarbonylation of ethene when used in combination with H 2 SO 4 and PPh 3 . The influence of the following operating conditions on the catalytic activity have been studied: (i) H 2 SO 4 /Pd ratio; (ii) PPh 3 /Pd ratio; (iii) total pressure with CO/ethene = 1/1; (iv) pressure of one gas at constant pressure of the other; (v) H 2 O concentration; (vi) temperature. At 100 °C a TOF = 2168 h −1 has been achieved when the catalytic system is used in the ratios Pd/H 2 SO 4 /P = 1/107/18 (mol/mol), under 6 bar (CO/E = 1/1), H 2 O concentration 0.16% in MeOH by weight. After catalysis and upon addition of LiCl, trans- [Pd(COEt)Cl(PPh 3 ) 2 ], which is related to the “Pd–H” catalytic cycle, has been isolated. Cis -[Pd(SO 4 )(PPh 3 ) 2 ] in CD 2 Cl 2 /MeOH reacts with CO to give a PdCOOMe complex (related to the “carbomethoxy mechanism”), which neither inserts ethene, nor gives methyl propanoate (MP). In the presence of H 2 O and H 2 SO 4 the carbomethoxy complex is unstable giving a Pd–H complex, which yields catalysis to MP in the presence of CO and ethene. The “Pd–H” and “Pd–COOMe” catalytic cycles are discussed on the basis of the influence of the operating conditions on the TOF and of NMR evidences.

The reduction of mandelic acid derivatives (ArCHOHCOOH) to phenylacetic acid derivatives by carbon monoxide catalyzed by a PdHCl system easily occurs when the aromatic ring is para -substituted with a hydroxy group. Other electron-releasing substituents such as a methoxy group have a much lower promoting effect. The reaction practically does not occur with mandelic acid. A compound of Pd(II), such as PdX 2 , [Pd(1,3-η-C 3 H 5 )Cl] 2 ] or PdX 2 (PPh 3 ) 2 (X  Cl, AcO) can be used as catalyst precursor. The reaction occurs to an appreciable extent only in the presence of HCl. Under the reaction conditions tested (70–110 °C, 50–100 atm of carbon monoxide, benzene-ethanol as reaction medium, [Pd(II)] = 10 −3 −10 −2 M, substrate/HCl/Pd = 100:50:1) decomposition to Pd metal occurs. Pd/C can also be used: it gives practically the same results as the precursors listed above. The key steps of the proposed catalytic cycle are: (i) the chloride ArCHClCOOR (R  H, Et), formed in situ by substitution of the α-hydroxy group of ArCHOHCOOR upon reaction with HCl, oxidatively adds to a Pd(O) species with formation of a catalytic intermediate having a Pd[CH(Ar)COOR] moiety; (ii) the PdC σ-bond of this species inserts carbon monoxide, yielding an acyl intermediate of the type Pd[COCH(Ar)COOR]; (iii) nucleophilic attack of ROH on the carbon atom of the carbonyl ligand yields a phenylmalonic acid derivative which splits off CO 2 yielding the final product, ArCH 2 COOR. Alternatively, H + may react with the intermediate formed in step (i), yielding directly the final product and a Pd(II) species, which is reduced by CO to Pd(O), which starts another catalytic cycle. The promoting effect of the hydroxy substituent in para position is discussed in terms of resonance structures. This reaction is compared with the carbonylation of aromatic aldehydes to ArCH 2 COOR, catalyzed by a PdPPh 3 HCl system. Also in this case there is a marked promoting effect of a hydroxy substituent in the para position. However, the carbonylation of the aldehydes occurs only in the presence of both PPh 3 and HCl, at variance with the reductive carbonylation described in this paper, where this ligand does not play any major role.

The catalytic activity of the [PdCl 2 (dppp)] complex in the 1-olefin/ethene (E)/CO terpolymerisation has been studied in MeOH (containing 1000 ppm of H 2 O) as a solvent. The 1-olefins tested were propene (P), 1-hexene (Hex), 1-decene (D) and styrene (S). At 90 °C and 45 atm (E/CO = 1/1), the system [PdCl 2 (dppp)]/TsOH ( p -toluenesulfonic acid) = 1/8 catalyses efficiently the reactions leading to 5000 g PECO/(g Pd h), 5600 g HexECO/(g Pd h), 5650 g DECO/(g Pd h) and 4100 g SECO/(g Pd h). In particular, it has been studied deeper the effect of Hex and S concentrations on productivities, average molecular weights and melting temperatures of HexECO and SECO, respectively. A mechanism of reaction has been also proposed and discussed, supported by IR, and NMR characterizations.

The cationic complexes trans-[Pd(COOR)(H2O)(PPh3)2](TsO) have been synthesised by reacting cis-[Pd(H2O)2(PPh3)2](TsO)2·2H2O with CO in ROH (R = Me and Et), practically under room conditions, or by methathetical exchange of trans-[Pd(COOMe)Cl(PPh3)2] with Ag(TsO) (R = n-Pr, iso-Pr, n-Bu, iso-Bu, sec-Bu). They have been characterised by IR, 1H NMR and 31P NMR spectroscopies. The X-ray investigation of trans-[Pd(COOMe)(TsO)(PPh3)2] reveals that the palladium center is surrounded in a virtually square planar environment realized by two PPh3 trans to each other, the carbon atom of the carbomethoxy ligand and an oxygen atom of the p-toluensulfonate anion, with two crystallization molecules of CHCl3. The Pd–O–S angle, 151.9 (3)°, is very wide, probably due to the interaction of one CHCl3 molecule with the complex inner core. The carbomethoxy derivatives react with R′OH yielding the corresponding R′ carboalkoxy derivative (R′ = Et, n-Pr and iso-Pr); ethene does not insert into the Pd–COOMe bond; decarbomethoxylation occurs when treated with TsOH/H2O in MeOH at 50 °C. All the carboalkoxy are precursors for the catalytic carboalkoxylation of ethene if used in combination of PPh3 and TsOH, better in the presence of some water. Experimental evidences are more in favor of the so-called “hydride” mechanism rather than the “carbomethoxy” mechanism.

Homogeneous and heterogeneous Pd-based catalysts (in the presence of Co(acac)3/ligand/BQ/TBAB and molecular sieve 4A), have been compared in the oxidative carbonylation of phenols. The best yields have been observed in the presence of bulky bidentate N-N ligands such as dmphen and triind. The comparison between homogeneous and heterogeneous systems shows similar behavior in terms of yield and selectivity in DPC, as in 4 h of reaction only small differences of activity have been observed. On the contrary, in 20 h of reaction only the systems Pd(OAc)2/Co(acac)3/dmphen/BQ/TBAB and Pd(OAc)2/Co(acac)3/triind/BQ/TBAB double the yield in DPC, while with the other systems the conversion is blocked. The beneficial effect of the ligands and of TBAB might be due to their capacity of inhibiting the growing of Pd nanoparticles that are likely to form, thus easing their reoxidation to Pd(II) species. The initial rate of phenol or methyl substituted phenols in CH2Cl2 as a solvent are only slightly influenced, except in the case of bulkier 2,6-dimethylphenol. The conversion vs. time profile evidences that fast catalyst deactivation occurs in any case.

Aromatic aldehydes having electron-releasing para substituents, such as a hydroxy group, are carbonylated to phenylacetic acid derivatives in the presence of a PdPPh3HCl catalytic system, at 90–120 °C, 50–100 atm of carbon monoxide, 1–2 h, in the presence of water or an alkanol. PPh3 and HCl play key roles in the catalysis, since in their absence no activity is observed. When a Pd(II) compound, such as PdCl2, Pd(AcO)2, Pd(PPh3)Cl2, [Pd(1,3-η-C3H5)Cl]2, is used as catalyst precursor, partial decomposition to palladium metal occurs. Pd/C is also active, provided that PPh3 and HCl are present. The catalytic system is more active when an excess of PPh3 and HCl is used. Vanillin (4-hydroxy-3-methoxy-benzaldehyde) is carbonylated with 70–75% yields when catalyst and reagents are employed in the ratio Pd(II)/PPh3/HCl/aldehyde/alkanol = 1/6/100/100/800–1000, in a solvent such as dioxane, benzene or dichloroethane ([Pd] = 10−2 M). Higher yields are achieved with primary alkanols, except with MeOH. In t-BuOH only trace amounts of product are obtained because the alkanol subtracts HCl, yielding t-BuCl. The yield increases on increasing the concentration of EtOH added to the solvent and reaches a maximum of ca. 75% when the ratio EtOH/solvent = 1/1, while it is lower (55%) when EtOH alone is used. The yield increases on increasing the carbon monoxide pressure and the concentration of the catalyst, and is almost independent of the aldehyde concentration. In the proposed catalytic cycle it is suggested that a chloride of type ArCH(OR)Cl (RH, alkyl radical of the alkanol, formed in situ by addition of HCl to the C double bond of the aldehyde, oxidatively adds to a Pd(0) species with formation of an intermediate having a Pd - [CH(OR)Ar moiety, which, upon insertion of carbon monoxide followed by interaction with the alkanol or water, yields a mandelic acid derivative, ArCH(OR)COOR. HCl reacts with this product with formation of the corresponding chloride, ArCHClCOOR, which in turn gives oxidative addition to a Pd(0) species to form an organopalladium(II) intermediate having a PdCH(COOR)Ar bond. Successive insertion of carbon monoxide and interaction with water or the alkanol yields a phenylmalonic acid derivative, which, upon decarboxylation, leads to the final product, ArCH2COOR.

The system [PdCl2(PPh3)2]/PPh3/HCl catalyses the carbonylation of ethene in MeOH as a solvent to give methyl propanoate (MP) or a polyketone (PK). The influence of temperature, Pd/P, CO/ethene and Pd/HCl ratios, and concentration of H2O on the catalytic activity has been studied. The catalytic system is active only in the presence of HCl and is stable when P/Pd is ≥6/1 up to 110 °C. At 100 °C, with Pd/P/HCl = 1/6/1600 (HCl initially added), under 6.0 MPa total pressure, the main product is MP at 1.0 MPa of ethene, whereas is PK when the pressure of the olefin is higher than 4.0 MPa. Water, which forms in the solvent, because of the reaction of MeOH with HCl, has a minor effect. The PK product presents a 2.5–4/1 ratio between the keto and ester end groups. The proposed catalytic cycle takes into account the results.