530112-06-2Relevant academic research and scientific papers
Synthesis, characterization and X-ray structure of trans-[Pd(COOCH3)(H2O)(PPh3)2] (TsO), a possible intermediate in the catalytic hydroesterification of olefins (TsO = p-toluenesulfonate)
Cavinato, Gianni,Vavasori, Andrea,Toniolo, Luigi,Benetollo, Franco
, p. 183 - 188 (2003)
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.
New carboalkoxybis(triphenylphosphine)palladium(II) cationic complexes: Synthesis, characterization, reactivity and role in the catalytic hydrocarboalkoxylation of ethene. X-ray structure of trans-[Pd(COOMe)(TsO)(PPh3)2]·2CHCl3
Amadio,Cavinato,Dolmella,Ronchin,Toniolo,Vavasori
, p. 103 - 110 (2009/04/12)
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.
