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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.

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 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 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.

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 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.

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 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 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.

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 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.

PdCl 2 (PPh 3 ) 2 , in combination with HCl, is highly active in the alkoxycarbonylation of α,β-ketocycloolefins to 3-oxocycloalkanecarboxylic acid esters. The reaction is region specific. The catalytic system is stabilized by addition of PPh 3 , which depresses the activity but prevents decomposition to inactive palladium metal. Typical reaction conditions are: Pd/P/cyclohexenone/HCl=1/2–4/200–600/50–100; [Pd] = 0.1−1·10 −2 mol l −1 ; P CO = 100 atm; temperature 100°C; solvent dioxane, THF, or benzene. With 2-cyclohexen- 1 -one the effect of the following variables on the yield has been examined: temperature, pressure of carbon monoxide, concentration of cyclohexenone, ethanol, catalyst, Pd P ratio, cyclohexenone/HCl ratio, reaction time, and solvent. As expected the yield increases with increasing reaction time, pressure of carbon monoxide, concentration of catalyst at constant Pd P ratio, and temperature. The yield passes through a maximum when increasing the concentration of HCl and EtOH, after which the yield decreases because the catalyst decomposes to palladium metal. The yield is almost insensitive to the polarity of solvents such as dioxane, THF, or benzene, but it rather depends on the bulkyness of the alkanol as the reaction rate decreases in the order: MeOH > EtOH > n-PrOH > n-BuOH > s-PrOH. The proposed reaction mechanism proceeds through the following steps. (i) The starting Pd II precursor is reduced to a Pd 0 complex which gives oxidative addition of HCl with formation of a Pd-hydride species; (ii) cyclohexenone inserts into a PdH bond giving a β-ketocyclohexyl-Pd intermediate; (iii) this inserts CO with formation of the corresponding carbonyl derivative; (iv) alcoholysis of this intermediate yields the final product with regeneration of the hydride. The reaction is region specific because of the keto group which directs the anti-Markownikoff addition of PdH to the conjugated CC double bond.

The catalytic system PdCl 2 (PPh 3 ) 2 HCl is highly active and selective in the hydrogen transfer reaction from H 2 OCO to PhCOCH 2 CHOHCOOH which yields the corresponding γ-keto acid PhCOCH 2 CH 2 COOH, with concomitant evolution of CO 2 . An increase of temperature, pressure of carbon monoxide and catalyst concentration have a beneficial effect on the reaction rate, which appears to be of the first order in the substrate and passes through a maximum when varying the concentration of HCl. It is proposed that one important function of HCl is to give rise to chloride PhCOCH 2 CHClCOOH which interacts with a palladium hydride that takes origin from the decarboxylation of a species having a PdCOOH moiety, which in turn results from the interaction of H 2 O and CO on the metal center. The yield passes through a maximum on increasing the concentration of H 2 O. This trend is attributed to the fact that, on one hand, H 2 O favors the formation of the PdCOOH species, while, on the other hand, it may compete with other reacting molecules for coordination to the metal center. Moreover, H 2 O does not favor the formation of the chloride. When employed in relatively high concentration, the catalyst precursor has been recovered as a complex of palladium(0), Pd 3 (CO) 3 (PPh 3 ) 3 or Pd(CO)(PPh 3 ) 3 , the latter in the presence of PPh 3 . The reduction to palladium(0) takes place only in the presence of H 2 O and is likely to occur via the intermediacy of a PdCOOH species, which after CO 2 evolution gives the reduced complex probably via reductive elimination of HCl from the hydride intermediate trans -PdHCl(PPh 3 ) 2 . Moreover, PhCOCHCHCOOH in combination with HCl (equivalent to PhCOCH 2 CHClCOOH) reacts with Pd(CO)(PPh 3 ) 3 to give the hydrogenated product PhCOCH 2 CH 2 COOH and PdCl 2 (PPh 3 ) 2 . On the basis of these results, and knowing that HCl reacts with Pd(CO)(PPh 3 ) 3 to give the hydride PdHCl(PPh 3 ) 2 , it is proposed that the catalytic cycle proceeds through the following steps: (i) H 2 O and CO interact with the metal center of the precursor yielding a PdCOOH species, (ii) this gives off CO 2 with formation of a hydride, (iii) this interacts with chloride PhCOCH 2 CHClCOOH to yield the product PhCOCH 2 CH 2 COOH and the palladium(II) precursor back to the catalytic cycle.

A PDHCl catalytic system is highly active and selective in the hydrogen transfer from H 2 OCO to the olefinic double bond of the unsaturated γ-ketoacid PhCOCHCHCOOH to PhCOCH 2 CH 2 COOH. Typical reaction conditions are: P CO : 20–30 atm; Pd/substrate/H 2 O/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. High yields are obtained only when the palladium catalyst is used in combination with HCl. When a palladium(II) catalyst precursor is employed, extensive decomposition to palladium metal occurs. Pd/C shows also high activity. The proposed catalytic cycle proceeds through the following steps. (i) Addition of HCl to the olefinic double bond of the starting substrate gives the chloride PhCOCH 2 CHClCOOH, which oxidatively adds to “reduced palladium”, with formation of a catalytic intermediate having a Pd[CH(COOH)CH 2 COPh] moiety. “Reduced palladium” is the metal coordinated by other atoms of palladium, and/or by carbon monoxide. (ii) H 2 O and CO react on the metal center of this species giving an intermediate having also a carbohydroxy ligand, (HOOC)Pd[CH(COOH)CH 2 COPh]. (iii) β-hydride abstraction from the carbohydroxy ligand gives a hydride HPd[CH(COOH)CH 2 COPh], with evolution of CO 2 . (iv) Finally, reductive elimination of the product PhCOCH 2 CH 2 COOH returns the catalyst to the catalytic cycle. Alternatively, protonolysis of the intermediate formed in the first step yields directly the final product and a Pd(II) species, which is reduced by CO and H 2 O to palladium metal back into the catalytic cycle. This is supported by the fact that when PhCOCHCHCOOH is allowed to react with a stoichiometric amount of Pd/C, in the presence of HCl and of CO and in the absence of H 2 O, PhCOCH 2 CH 2 COOH is formed in a significant amount.

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.

[PdCl 2 (PPh 3 ) 2 ] suspended in MeOH reacts with carbon monoxide (40–80 atm, 50°C), in the presence of a base such as NEt 3 to give the methoxycarbonyl complex trans -[PdCl(COOMe)(PPh 3 ) 2 ]. When the carbonylation reaction is carried out at 90–100°C reduction to Pd 0 carbonyl-phosphine complexes occurs, with formation of dimethyl carbonate, selectively and in an almost quantitative yield. The above complexes are less reactive than the acetato-analogues, which give dimethyl oxalate as the main organic carbonylation product even at 50°C.

A palladium-based catalytic system is highly active in the synthesis of γ-keto acids of type ArCOCH 2 CH 2 COOH via carbonylation-decarboxylation of the corresponding α-chloride. Typical reaction conditions are: P (CO) = 20–30 atm; substrate/H 2 O/Pd = 100–400/800–1000/1 (mol); temperature: 100–110 °C; [Pd]=0.25 × 10 −2 −1 × 1O −2 M; solvent: acetone; reaction time: 1–2 h. A palladium(II) complex can be used as catalyst precursor. Under the reaction conditions above, reduction of the precursor to palladium metal occurs to a variable extent. High catalytic activity is observed when the precursor undergoes extensive decomposition to the metal. Pd/C is also highly active. Slightly higher yields are obtainable when the catalytic system is used in combination with a ligand such as PPh 3 . A mechanism for the catalytic cycle is proposed: (i) The starting keto chloride undergoes oxidative addition to reduced palladium with formation of a catalytic intermediate having a Pd-[CH(COOH)CH 2 COPh] moiety. The reduced palladium may be the metal coordinated by other atoms of palladium and/or by carbon monoxide and/or by a PPh 3 ligand when catalysis is carried out in the presence of this ligand. It is also proposed that the keto group in the β-position with respect to the carbon atom bonded to chlorine weakens the CCl bond, easing the oxidative addition step and enhancing the activity of the catalyst. (ii) Carbon monoxide ‘inserts’ into the PdC bond of the above intermediate to give an acyl catalytic intermediate having a Pd-[COCH(COOH)CH 2 COPh] moiety. (iii) Nucleophilic attack of H 2 O to the carbon atom of the carbonyl group bonded to the metal of the acyl intermediate yields a malonic acid derivative as product intermediate. This, upon decarboxylation, gives the final product. Alternatively, the desired product may form without the malonic acid derivative intermediate, through the following reaction pathway: the acyl intermediate undergoes decarboxylation with formation of a different acyl intermediate, having a Pd-[CO-CH 2 CH 2 COPh] moiety, which, upon nucleophilic attack of H 2 O on the carbon atom of the carbonyl group bonded to the metal, yields the final product.

The acyl complex PdCl(COR)(PPh3)2 (R = Et, n-Hex), isolated during the course of hydrocarbalkoxylation reactions catalyzed by the precursor system PdCl2(PPh3)2-PPh3 (95°C, P(CO) 100–120 atm; Pd: P = 1:3–4), in ethanol or higher alkanols as solvents, reacts with an alkanol R'OH in the presence of added PPh3 (Pd: P = 1:3) to yield the ester RCOOR′and a mixture of PdCl2(PPh2)2 and Pd(PPh3)3 or 4. Moreover, when it is employed as catalyst precursor (R = n-Hex; Pd: P = 1:4) in the hydrocarbalkoxylation of ethylene, it is recovered as its ethyl analog and it yields almost stoichiometric amounts of n-HexCOOR′. When the di carbomethoxy complex PdCl(COOMe)(PPh3)2, isolated in mixture with PdCl(COR)(PPh3)2 in hydrocarbomethoxylation experiments, is treated with 1-hexene in methanol (Pd: P:1-hexene : MeOH = 1:3:40:125), under nitrogen, in the absence of carbon monoxide, at 95°C, methyl heptanoate ester is not formed, and the starting complex is recovered almost quantitatively (92%). When PdCl2(PPh3)2 or PdCl(COOMe)(PPh3)2 are used as catalyst precursors for the carbonylation of 1-hexene in MeOH, in the absence of added PPh3 and in the presence of NEt3 or of carboxylic acid anions (both of them are known to favor the formation of the carbomethoxy complex), no catalytic activity is observed and the precursors are recovered as palladium(0)carbonylphosphine complexes, ultimately mixed with the carbomethoxy complex. The results suppport the view that, of the two commonly accepted mechanisms for the catalytic hydrocarbalkoxylation of olefins, involving MH or MCOOR′ addition to the olefinic double bond, only the first one, in which a key intermediate is a Pd-acyl species, is probably involved. When n-BuOH is isued as solvent the catalytic activity remains high even after 5–6 reuses of the catalyst, whereas in MeOH the activity falls significantly below its initial value because of decomposition of the catalyst into inactive palladium(0) complexes and palladium metal, probably via a carbomethoxypalladium complex.

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 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.

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.

Trans -[PtCl(COPr-n)(PPh 3 ) 2 ] (I) has been isolated in good yield from the mixtures obtained by treating a mixture of propene, cis -[PtCl 2 (PPh 3 ) 2 ] and SnCl 2 · H 2 O with carbon monoxide in the presence or absence of hydrogen in an alcohol in which no significant hydroformylation or hydroxycarboalkylation actually occurs. The cis -[PECl 2 (PPh 3 2 ]-SnCl 2 · 2 H 2 O system is highly active in the catalytic hydroformylation in methyl isobutyl ketone, and from reaction mixtures in this medium trans -[Pt(SnCl 3 )(COPr-n)(PPh 3 ) 2 ] (II) has been isolated (33% yield). The presence of a PtSn bond in a complex of type II plays a key role in promoting the formation of the aldehyde from the acyl derivative, but it is not necessary for the formation of intermediate I, since this can be isolated in good yield even in the absence of the tin compound. The higher regioselectivity observed using intermediate I or II, compared with that when the precursor is used is discussed in terms of steric effects of the ligands competing for coordination to the platinum atom. The catalytic properties of complex I are compared also with those of its palladium analog, which catalyzes only the hydrocarbo

[Re(CO) 3 (PPh 3 ) 2 Cl] reacts with Li(ArNxxxXxxxNAr) (X = CH, N; Ar = p -CH 3 C 6 H 4 , C 6 H 5 , p -ClC 6 H 4 , p -FC 6 H 4 in boiling THF to yiled[[Re(CO) 2 (PPh 3 ) 2 - (ArNxxxXxxxNAr)]. The structure of these new complexes and the mode of coordination of the organonitrogen ligand are discussed on the basis of i.r. and 1 H n.m.r spectra

The title compound [Pt(CCPh)(HNNC 6 H 4 F- p )(PPh 3 ) 2 ](BF 4 ) has been synthesized from Pt(HCCPh)(PPh 3 ) 2 and p -FC 6 H 4 N 2 BF 4 , and a mechanism for its formation is proposed; X-ray diffraction studies show that the acetylide ligand is σ-bonded and that the PCCC system is essentially linear, while the diazene ligand has a trans configuration around the NN bond, and the hydrogen-bearing nitrogen atom is coordinated to the platinum.