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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%.

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.

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 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.

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.

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.

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.

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 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.

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.

Polyketone polymer -[-CO-CH(2)-CH(2)-](n)-, obtained by copolymerization of ethene and carbon monoxide, is utilized for immobilization of three different enzymes, one peroxidase from horseradish (HRP) and two amine oxidases, from bovine serum (BSAO) and lentil seedlings (LSAO). The easy immobilization procedure is carried out in diluted buffer, at pH 7.0 and 3 degrees C, gently mixing the proteins with the polymer. No bifunctional reagents and spacer arms are required for the immobilization, which occurs exclusively via a large number of hydrogen bonds between the carbonyl groups of the polymer and the -NH groups of the polypeptidic chain. Experiments demonstrate a high linking capacity of polymer for BSAO and an extraordinary strong linkage for LSAO. Moreover, activity measurements demonstrate that immobilized LSAO totally retains the catalytic characteristics of the free enzyme, where only a limited increase of K(M) value is observed. Finally, the HRP-activated polymer is successfully used as active packed bed of an enzymatic reactor for continuous flow conversion and flow injection analysis of hydrogen peroxide containing solutions.

The title complex has been synthesized by first reacting dppp with Pd(AcO)2 in acetone and then with NaHSO4 in water. It has been characterized by IR, NMR and X-ray diffraction studies. The 31P NMR spectrum in DMSO shows a singlet at 16.62 ppm indicating that the two P atoms are equivalent and that the sulfate anion is weakly coordinating. The X-ray structure shows that the Pd atom is surrounded in an almost regular square planar environment by the two P atoms and by two O atoms of the sulfate anion and that the neutral complex is accompanied by a water molecule of crystallization. The Pd–P distances (2.217(1) and 2.233(1)) and the P–Pd–P angle (90.78(3)°) are close to those found in other complexes where the chelating diphosphine is the same. Also the Pd–O distances and the O–Pd–O bond angle are comparable to those of other relevant chelating ligands. In MeOH, the title complex, in combination with H2SO4, catalyses the CO-ethene copolymerization. The productivity reaches a maximum upon increasing the H2SO4/Pd ratio up to ca. 470 (7650 g of polyketone/g Pd h at 90 °C and 45 atm, CO/ethene 1/1). The viscosity of the polyketone passes through a maximum of 0.95 dL/g in m-cresol when the above ratio is ca. 100. It has been proposed that acid promotes the copolymerization process by destabilizing the β- and γ-chelates intermediates involved in chain growing process, thus favoring the insertion of the monomers. At relatively high acid concentration the lowering of productivity and viscosity suggests that the sulfate anion competes with the monomers for the coordination to the metal center. In H2O–CH3COOH as a solvent the productivity strongly depends on the H2O/CH3COOH ratio, as it passes through a maximum of 12 000 g polymer/g Pd h in the presence of ca. 60% of H2O. The productivity is significantly lower than that found when the acetate and chloride analogues are used (27 000 g polyketone/g Pd · h). Thus, it is likely that the sulfate anion assists significantly the copolymerization process even though the concentration of CH3COOH/CH3COO− is much preponderant.

The influence of promoters and precipitants of the catalyst precursor on the activity and selectivity of the hydrogenation of benzene to cyclohexene catalyzed by highly loaded oxide-promoted Ru/ZrO2catalysts, carried out in a tetraphase reactor (in the presence of an aqueous solution of ZnSO4), at 423 K and 5 Mpa, was studied. The effect of hydrogen diffusion on the reaction kinetics and on the selectivity has been taken into consideration, the internal pore diffusion being actually the limiting step. Hydrogen chemisorption measurements indicate that the catalyst activity is not influenced by the Ru dispersion, but rather by weakly chemisorbed species.

In MeOH, [Pd(AcO)2(dppp)] becomes an efficient catalyst for the perfectly alternated CO-C2H4 copolymerization when used in combination of a relatively large amount of CH3COOH (CH3COOH/Pd, ca. 2.0×104). Under 4.56 MPa (CO/C2H4 = 1/1), at 90 °C, 7.5 kg polyketone/g Pd∗h are obtained. A significantly higher productivity is obtained in H2O-CH3COOH, in place of MeOH (27.5 kg polymer/g Pd∗h under 4.56 MPa (CO/C2H4 = 1/1), 90 °C, H2O=37% (mol/mol)). Under these conditions the catalyst undergoes only a minor deactivation with time as after 3 h the productivity decreases only by ca. 10%. The 13 C NMR analysis shows that [Pd(AcO)2(dppp)] in CH3COOH-H2O yields a perfectly alternated polyketone of ca. 8000 g/mol bearing only ketonic end groups. During the course of the copolymerization reaction CO2 forms in significant amount. These findings suggest that the insertion of C2H4 into PdH bond starts the catalytic cycle, and that alternating insertions of the monomers followed by protonolysis of a PdC bond of a Pd-CH2-CH2-(CO-C2H4)n-H growing chain yields the polymer with only keto ending groups and a Pd-OH species; a reaction closely related to the WGS reproduces the starting Pd-hydride; deprotonation of this species to inactive Pd(0) is prevented by the acid.

The complex trans-[Pd(COOCH3)(H2O)(PPh3)2](TsO) (I) has been synthesized by reacting trans-[Pd(COOCH3)Cl(PPh3)2] with AgTsO in methanol. It has been characterized by IR, 1H and 31P NMR spectroscopy. Crystals of trans-[Pd(COOCH3)(H2O)(PPh3)2](TsO)·(CH3OH) (II) have been obtained by re-crystallization of I in methanol. The structure of the complex has been determined by X-ray analysis. It shows a slightly distorted square planar conformation around the central palladium. The coordinated water molecule and the clathrated methanol form a contact with the uncoordinated TsO− anion, suggesting hydrogen bond interaction. Since I is a possible intermediate in the catalytic hydroesterification of olefins, its catalytic activity in the hydroesterification of ethylene has been tested at 100 °C under 45 atm of a 1/1 mixture of ethylene and CO in methanol as solvent, also in the presence of PPh3 and TsOH. Without addition of PPh3 and TsOH, I affords to traces of methylpropionate together with Pd(0) complexes and Pd metal. The same results are obtained when complex I is tested in the presence of PPh3, except that in this case formation of palladium metal is avoided. Using the system I/PPh3/TsOH=1/6/8, a TOF (mol of ester/mol Pd∗h) of 1800 h−1 is obtained. We propose that the role of the acid TsOH is to favor the formation of a Pd–hydride intermediate and/or to reactivate the Pd(0) species, stabilized by the excess of PPh3, via an oxidative addition of the acid. Since the acid does not favor the formation of Pd–alkoxy species we suggest that complex I plays only a minor role in catalysis and that this occurs via a Pd–hydride species.

Hydroesterification of ethylene to methyl propionate has been studied using the catalyst precursor Pd(PPh3)2(TsO)2, which is active in presence of PPh3 and TsOH (TOF=5700 h−1 at 120°C, 40 atm (CO/C2H4=1/1), Pd/PPh3/TsOH=1/8/10, [Pd]=2×10−3 mol l−1, solvent methanol, H2O=800 ppm). In this paper we study the promoting effect of a hydride source, molecular hydrogen, water and p-toluenesulfonic acid (TsOH) and the inhibiting effect of p-benzoquinone. On the basis of experimental evidences, of the two possible initial steps of the catalytic cycle, the insertion of the olefin into a Pd H species or into a Pd OCH3 species, it is suggested that the first plays a more important role.

The reactivity of Ru based catalysts in the benzene selective hydrogenation to cyclohexene has been studied. The reaction has been carried out 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 0.6 mol l 1 ZnSO4. A detailed kinetic measurement has been carried out in order to study the influence of the preparation procedure and of the treatments on the catalyst activity and selectivity. Moreover, a comparison of benzene and cyclohexene hydrogenation kinetics is presented in order to evaluate, which are the influence of the treatments carried out on the unreduced catalyst on the activity, selectivity and yield to cyclohexene. The kinetics of benzene hydrogenation indicates that the catalyst activity is influenced by the time, during which it remains in the mixture of precipitation for its preparation. The longer the time, the lower the activity is. Selectivity and yield remain practically unaffected after 18 h of permanence in the mixture of precipitation. Treatment of the unreduced catalyst with water depresses both activity and selectivity, while treatment with 1 mol l 1 NaOH gives the best results. On the contrary, in the hydrogenation of cyclohexene, the NaOH treated catalyst is three times less active than the catalyst treated with water. These results are in agreement with the higher selectivity achieved using NaOH treated catalysts. © 2000 Elsevier Science B.V. All rights reserved.

A PdHCl catalytic system is highly active in the synthesis of γ-ketoacids of type ArCOCH2CH2COOH via reduction with CO of the ketohydroxy acids ArCOCH2CHOHCOOH. Typical reaction conditions are: PCO: 20–30 atm; Pd/ substrate/H2O/HCl = 1/400–1000/800–3000/ 100–1000 (mol); temperature: 100–110°C; [Pd]: 10−3 to 10−2 M; solvent: dioxane; reaction time: 1–2 h. The reaction occurs in high yield only when the palladium precursor is used in combination with HCl and in the presence of H2O. Under the reaction conditions employed, the palladium(II) complex used as catalyst precursor decomposes to palladium metal. Pd/C is also highly active. It is proposed that the catalytic cycle proceeds through the following steps: (i) The chloride ArCOCH2CHClCOOH, which forms in situ from the starting substrate and HCl, undergoes oxidative addition to reduced palladium with formation of a catalytic intermediate having a Pd-[CH(COOH)CH2COPh] moiety. (ii) Interaction of H2O and CO on the metal yields an intermediate having also a carbohydroxy ligand, (HOOC)-Pd-[CH(COOH)CH2COPh]. (iii) This intermediate, after β-hydride abstraction from the carbohydroxy ligand, gives off CO2 and reductive elimination gives product PhCOCH2CH2COOH. Alternatively, HCl may react with the intermediate proposed in step (i), yielding directly the product and a Pd(II) species, which is reduced by CO to a Pd(0) species, which starts another catalytic cycle.

Pt/charcoal catalysts with platinum contents in the range 1.2–11.3 wt%, as used in a slurry reactor for the production of hydroxylamine by hydrogenation of nitric oxide in a sulfuric acid environment, have been microstructurally characterized by small angle X-ray scattering, line-broadening analysis of wide angle X-ray scattering profiles, and transmission electron microscopy. The microstructural data are related to the results of chemisorption analysis and to the catalytic rates of hydroxylamine production, giving a better insight into the catalytic process.

The hydrido-1,3-di- p -tolyltriazenido complex of platinum(II) trans -[Pt(PPh 3 ) 2 H( p -CH 3 C 6 H 4 NNNC 6 H 4 CH 3 - p )] reacts with CO, 2,6-Me 2 C 6 H 3 NC, PPh 3 and PhCCPh under mild conditions to yield platinum(0) complexes by reductive elimination of 1,3-di- p -tolyltriazene.

Summary The reaction of trans -PtCl(COR)(PPh 3 ) 2 ( 1 ) (R = a , C 6 H 5 ; b , C 6 H 4 - p -NO 2 ; c C 6 H 4 - p -CH 3 ; d , C 6 H 4 - p -OCH 3 ; e , CH 3 , f , Et; g , Pr n ; h , Hex n ; i , CH 2 CH 2 Ph; j , Bu t ) with SnCl 2 and SnCl 2 plus H 2 are described. The reactions with SnCl 2 alone afford a mixture of trans -Pt(SnCl 3 )(PPh 3 ) 2 ( 2 ), and trans -PtCl(C(OSnCl 2 )-R)(PPh 3 ) 2 ( 3 ) with 3 having tin oxygen bond. For 1f, 1h and 1j , reactions with SnCl 2 plus H 2 give aldehydes and platinum(II) hydride complexes, whereas for 1b and 1d , no aldehydes are obtained. The significance of these results in relation to H 2 activation in the hydroformylation reaction is discussed. 31 P, 119 Sn, 195 Pt and, in a few cases, 13 C NMR data are presented.

The structure of the title compound has been determined at room temperature from three-dimensional X-ray data collected by counter methods. The material crystallizes in the triclinic space group P 1 with two molecules in a cell of dimensions a 14.649(2), b 15.082(2), c 10.929(1) A, α 110.99(5)°, β 102.40(5)°, γ 84.54(5)°. Full-matrix least-squares treatment of 4673 observed intensities gave an unweighted R value of 0.069. The platinum atom has square-planar coordination with PtP(1) 2.268(5), PtP(2) 2.267(5), PtN(1) 2.09(2) A. The presence of the hydrogen atom is inferred from IR and 1 H NMR data. The triazenido ligand, σ bonded to the metal through N(1), lies perpendicular to the coordination plane.

The system [PtCl2(PPh3)2]/SnCl2 significantly catalyzes only the hydroformylation of α-olefins at 100°C in EtOH, at P(CO)  P(H2)  65 atm; hydrocarboalkoxylation does not occur to an apreciable extent, even in the presence of potential activating agents (HCl, LiCl). The catalyst precursor has been recovered from the reaction medium, as the cationic complex [PtH(CO)(PPh3)2](SnCl3), having the SnCl3− anion non-directly bound to the platinum atom, and as trans-[PtCl(COR)(PPh3)2]. The latter complex is a (precursor) intermediate leading to an active catalytic species possessing at least one PtSn bond which plays a key role in the catalysis.

Thermolysis of (cis-bicyclo[6.1.0]nonatriene)diiron hexacarbonyl (FeFe) involves rearrangement of the starting organic moiety with formation of four iron carboyl complexes. The major product is the known cis-8,9-dihydroindeneiron tricarbonyl complex (VI). Two complexes have the same formula, C9H8Fe2(CO)5 (VII and VIII); VII can be also obtained by reaction of VI with Fe2(CO)9, while VIII is a methylpentalenediiron pentacarbonyl complex and represents a further example of stabilization of this reactive organic molecule by coordination; IX is probably a polycyclic cyclopentadienyl derivative [C9H9Fe(CO)2]2. Possible mechanisms for the formation of the four compounds are discussed.

The complex trans-[PtCl(COC6H13-n)(PPh3)2] (I) has been synthesized by treating cis-[PtCl2(PPh3)2] and 1-hexene with carbon monoxide under pressure in EtOH at 100°C. When in combination with SnCl2-2H2O, complex I is an intermediate precursor in the highly regioselective catalytic hydroformylation of 1-hexene, which readily occurs in a solvent such as a ketone. The crystal and molecular structure of complex I has been determined from three dimensional X-ray diffractometer data. The complex crystallizes in the triclinic space group P 1 . Cell parameters are as follows: a 15.869(8), b 12.306(8), c 11.437(7) A, α 109.8(1), β 76.6(1), γ 112.9(1)°, Z  2. Fullmatrix least-squares refinement converged at R  0.058 (Rw  0.064). The structure has approximately square planar geometry, and shows no unusual dimensions.

Among the several hydrides formed when trans-[PtHClL2] (L = PPh3) reacts with Sncl2, only trans-[PtH(SnCl3)L2] rapidly inserts ethylene, at −80°C, to yield cis-[PtEt(SnCl3)L2]. At −10°C, cis-[PtEt(SnCl3)L2] irreversibly rearranges to the trans-isomer, thus indicating that the cis-isomer is the kinetically controlled species, and that the trans-isomer is thermodynamically more stable. At −50°C, a mixture of trans-[PtHClL2] and trans[PtH(SnCl3)L2] reacts with ethylene to give cis-[PtEtClL2] and cis-[PtEt(SnCl3)L2] and this has been attributed to the catalytic activity of SnCl2 which dissociates from cis-[PtEt(SnCl3)L2] at this temperature. Carbon monoxide promotes the cis-trans isomerization of cis[PtEt(SnCl3)L2], which occurs rapidly even at −80°C. This rearrangement is followed by a slower reaction leading to the cationic complex trans-[PtEt(CO)L2]+ SnCl3−. At −80°C, this complex does not react further, but when it is kept at room temperature ethyl migration to coordinated carbon monoxide takes place, to give several Pt-acyl complexes, i.e. trans-[PtCl(COEt)L2], trans-[Pt(SnCl3)(COEt)L2], trans-[PtCl(COEt)l2 · SnCl2], and trans-[Pt(COEt)(CO)L2]+ SnCl3−. This mixture of Pt-acyl complexes reacts with molecular hydrogen to yield n-propanal and the same complex mixture of platinum hydrides as is obtained by treating trans-[PtHClL2] with SnCl2. Trans-[PtH(SnCl3)L2] reacts with carbon monoxide to yield the five-coordinate complex [PtH(SnCl3)(CO)2L2], which has been characterized by NMR and Ir spectroscopy; ethylene does not insert into the PtH bond of this complex at low temperature. At room temperature, trans-[PtH(SnCl3)L2] reacts with a mixture of CO and ethylene to yield the same mixture of Pt-acyl species as is obtained when trans-[PtEt(SnCl3)L2] is allowed to react with CO. The role of a PtSn bond in these reactions is discussed in relation to the catalytic cycle for the hydroformylation of olefins.

The complexes cis-PtCl(C2H5)(diphosphine) (diphosphine = 1,3-bis(diphenylphosphino)propane and 1,4-bis(diphenylphosphino)butane) have been used as model compounds for the hydroformylation of olefin catalyzed by the system PtCl2/diphosphine/SnCl2. They react with SnCl2 to yield the corresponding trichlorostannate complexes cis-Pt(SnCl3)(C2H5)(diphosphine), which in the absence of free ethylene decompose to form the dichloro species cis-PtCl2(diphosphine) via an unstable hydrido species. Both the chloro- and trichlorostannate-alkyl complexes react with CO to give the acyl species cis-PtX(COC2H5)(diphosphine) (X = Cl or SnCl3). When the diphosphine is 1,4-bis(diphenylphosphino)butane, oligomeric acyl complexes of trans geometry are formed. Preliminary studies of the reactivity of the acyl complexes with molecular hydrogen show that only the complexes bearing the Pt—SnCl3 moiety react at ambient conditions giving propanal as the only observed organic product.

This paper reports a study of the hydrogenation of nitric oxide to hydroxylamine in aqueous sulfuric acid in the presence of platinum supported on high-surface-area active carbon as catalyst. Industrially relevant catalysts (low Pt content and finely divided carbon particles) were used. In particular, conditions for the kinetic regime have been investigated. Measurements in the range 15–55 °C and on catalysts with platinum contents approximately from 1 to 11 wt% have been carried out. An activation energy of 11.8 Kcal/mol has been calculated.