24670-32-4Relevant articles and documents
On the mechanism of the hydrogen transfer from H2O-CO to γ-keto-α-hydroxy carboxylic acids to yield γ-keto acids catalyzed by a PdCl2(PPh3) 2 precursor in combination with hydrochloric acid
Cavinato,Toniolo
, p. 9 - 15 (1996)
The catalytic system PdCl2(PPh3)2-HCl is highly active and selective in the hydrogen transfer reaction from H2O-CO to PhCOCH2CHOHCOOH which yields the corresponding γ-keto acid PhCOCH2CH2COOH, with concomitant evolution of CO2. 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 PhCOCH2CHClCOOH 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 H2O and CO on the metal center. The yield passes through a maximum on increasing the concentration of H2O. This trend is attributed to the fact that, on one hand, H2O 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, H2O 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), Pd3(CO)3(PPh3)3 or Pd(CO)(PPh3)3, the latter in the presence of PPh3. The reduction to palladium(0) takes place only in the presence of H2O and is likely to occur via the intermediacy of a Pd-COOH species, which after CO2 evolution gives the reduced complex probably via reductive elimination of HCl from the hydride intermediate trans-PdHCl(PPh3)2. Moreover, PhCOCH=CHCOOH in combination with HCl (equivalent to PhCOCH2CHClCOOH) reacts with Pd(CO)(PPh3)3 to give the hydrogenated product PhCOCH2CH2COOH and PdCl2(PPh3)2. On the basis of these results, and knowing that HCl reacts with Pd(CO)(PPh3), to give the hydride PdHCl(PPh3)2, it is proposed that the catalytic cycle proceeds through the following steps: (i) H2O and CO interact with the metal center of the precursor yielding a Pd-COOH species, (ii) this gives off CO2 with formation of a hydride, (iii) this interacts with chloride PhCOCH2CHClCOOH to yield the product PhCOCH2CH2COOH and the palladium(II) precursor back to the catalytic cycle.
New aspects of the carbonylation of allylpalladium complexes
Bertani, R.,Cavinato, G.,Facchin, G.,Toniolo, L.,Vavasori, A.
, p. 273 - 276 (1994)
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 (n=3 or 4) or and trans- (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 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 complex trans-.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. Key words: Palladium; Allyl; Carbonylation
Characterization and catalytic activity of trans-[Pd(COCH2CH3)(TsO)(PPh3)2 ], isolated from the hydro-methoxycarbonylation of ethene catalyzed by [Pd(TsO)2(PPh3)2]
Cavinato, Gianni,Toniolo, Luigi,Vavasori, Andrea
, p. 233 - 240 (2008/10/09)
trans-[Pd(COCH2CH3)(TsO)(PPh 3)2] (I) was isolated after running the hydro-methoxycarbonylation (HMC) of ethylene. Complex (I) catalyzed the HMC of ethylene to methylpropanoate. Catalysis occurred via an initial
Palladium catalyzed hydrodechlorination of α-chloroacetophenones by hydrogen transfer from the H2O-CO system
Cavinato,Pasqualetto,Ronchin,Toniolo
, p. 15 - 22 (2008/10/09)
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 PdC12(PPh3)2 (II), it is proposed thai 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.
