The acyl complex PdCl(COR)(PPh3)2 (R = Et, hexyl), isolated during the course of hydrocarbalkoxylation reactions catalyzed by the precursor system PdCl2-(PPh3)2-PPh3, 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 mixt. of PdCl2(PPh2)2 and Pd(PPh3)3or4. Moreover, when it is employed as a catalyst precursor [R = hexyl (n-hex); Pd:P = 1:4] in the hydrocarbalkoxylation of ethylene, it is recovered as its Et analog and yields almost stoichiometric amts. of n-HexCOOR'. When the carbomethoxy complex PdCl(COOMe)(PPh3)2, isolated in mixt. with PdCl-(COR)(PPh3)2 in hydrocarbomethoxylation expts., is treated with 1-hexene in methanol (Pd:P:1-hexene:MeOH = 1:3:40:125), under nitrogen, in the absence of CO, at 95°, Me heptanoate is not formed, and the starting complex is recovered almost quant. (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 obsd. and the precursors are recovered as palladium(0) carbonyl phosphine complexes, ultimately mixed with the carbomethoxy complex. The results support the view that, of the two commonly accepted mechanisms for the catalytic hydrocarbalkoxylation of olefins, involving M-H or M-COOR' addn. to the olefinic double bond, only the first one, in which a key intermediate is a Pd-acyl species, is probably involved. When BuOH is used 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 decompn. of the catalyst into inactive palladium(0) complexes and palladium metal, probably via a carbomethoxypalladium complex.

On the mechanism of the hydrocarbalkoxylation of olefins catalyzed by palladium complexes

TONIOLO, Luigi
1990-01-01

Abstract

The acyl complex PdCl(COR)(PPh3)2 (R = Et, hexyl), isolated during the course of hydrocarbalkoxylation reactions catalyzed by the precursor system PdCl2-(PPh3)2-PPh3, 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 mixt. of PdCl2(PPh2)2 and Pd(PPh3)3or4. Moreover, when it is employed as a catalyst precursor [R = hexyl (n-hex); Pd:P = 1:4] in the hydrocarbalkoxylation of ethylene, it is recovered as its Et analog and yields almost stoichiometric amts. of n-HexCOOR'. When the carbomethoxy complex PdCl(COOMe)(PPh3)2, isolated in mixt. with PdCl-(COR)(PPh3)2 in hydrocarbomethoxylation expts., is treated with 1-hexene in methanol (Pd:P:1-hexene:MeOH = 1:3:40:125), under nitrogen, in the absence of CO, at 95°, Me heptanoate is not formed, and the starting complex is recovered almost quant. (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 obsd. and the precursors are recovered as palladium(0) carbonyl phosphine complexes, ultimately mixed with the carbomethoxy complex. The results support the view that, of the two commonly accepted mechanisms for the catalytic hydrocarbalkoxylation of olefins, involving M-H or M-COOR' addn. to the olefinic double bond, only the first one, in which a key intermediate is a Pd-acyl species, is probably involved. When BuOH is used 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 decompn. of the catalyst into inactive palladium(0) complexes and palladium metal, probably via a carbomethoxypalladium complex.
1990
398(1-2), 187-95
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in ARCA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10278/32880
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus ND
  • ???jsp.display-item.citation.isi??? ND
social impact