Synthesis of γ-ketocarboxylic acids via reduction of γ-keto-α-hydroxycarboxylic acids with carbon monoxide catalyzed by a PdHCl system
TL;DR: In this paper, 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(COO H)CH2COPh] moiety.
About: This article is published in Journal of Molecular Catalysis.The article was published on 1994-04-20 and is currently open access. It has received 8 citations till now. The article focuses on the topics: Palladium & Catalytic cycle.
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TL;DR: In this article, the catalytic system PdCl 2 (PPh 3 ) 2 HCl is highly active and selective in the hydrogen transfer reaction from H 2 O to PhCOCH 2 CH 2 COOH, with concomitant evolution of CO 2.
Abstract: The catalytic system PdCl 2 (PPh 3 ) 2 HCl is highly active and selective in the hydrogen transfer reaction from H 2 OCO 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 PdCOOH 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 PdCOOH 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 PdCOOH 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, PhCOCHCHCOOH 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 PdCOOH 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.
7 citations
TL;DR: In this paper, a PDHCl catalytic system is proposed, which is highly active and selective in the hydrogen transfer from H 2 O ǫ to the olefinic double bond of the unsaturated γ-ketoacid PhCOCHCHCOOH to PHCOCH 2 CH 2 COOH.
4 citations
TL;DR: In this paper, a PdCHCl catalytic system is proposed for the hydrogen transfer from H2O to ArCH2COOH for the synthesis of ArCH(Ar) substituted with a OH group.
Abstract: A PdCHCl catalytic system is highly active and selective in the hydrogen transfer from H2OCO to ArCHOHCOOH for the synthesis of ArCH2COOH (Ar is para substituted with a OH group). Typical reaction conditions are: temperature 50–70°C; PCO 20–80 atm; solvent; acetonitrile; substrate/Pd/HCl/H2O = 200–400/1/25–100/500–2000; [Pd] = 0.6−1.2 mmol·l−1. The reaction rate is approximately of the first order with respect to ArCHOHCOOH. The yield increases with the increasing of PCO and of the temperature, as expected, and passes through a maximum with the increasing of the concentration of H2O and of HCl. The proposed catalytic cycle proceeds through the following steps. (i) H2O and CO interact with the metal giving rise to an intermediate having a PdCOOH moiety, which, upon β-hydride abstraction, gives off CO2 with formation of a PdH species. (ii) The starting substrate is in equilibrium, in the presence of HCl, with the corresponding chloride ArCHClCOOH, which adds to the metal forming an intermediate having a PdCH(Ar)COOH moiety. (iii) This species interacts with the hydride yielding the product ArCH2COOH and regenerating the catalyst. The reaction is compared to the closely related catalyzed water gas shift reaction.
4 citations
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TL;DR: In this paper, a homogeneous palladium catalyst system was developed for the production of perfectly alternating copolymers of carbon monoxide with ethylene, where C 3 units randomly replace ethylene units along the chain.
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