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)

Abstract

The complex trans -[Pd (COOCH 3 (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 8C under 45 atm of a 1/1 mixture of ethylene and CO in methanol as solvent, also in the presence of PPh 3 and TsOH. Without addition of PPh 3 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 PPh 3 , except that in this case formation of palladium metal is avoided. Using the system I/PPh 3 /TsOH 0/1/6/8, 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 Á/ hydride intermediate and/or to reactivate the Pd(0) species, stabilized by the excess of PPh 3 , via an oxidative addition of the acid. Since the acid does not favor the formation of Pd Á/alkoxy species we suggest that complex I plays only a minor role in catalysis and that this occurs via a Pd Á/hydride species. #

Synthesis, characterization and catalytic activity in the carbonylation of ethene of cis-[Pd(H2O)2(PPh3)2]X2·nH2O (X=p-CH3C6H4SO3, n=2; X=CH3SO3, n=0). X-ray structure of cis-Pd(H2O)2(PPh3)2](p-CH3C6H4SO3)2·2H2O and of cis-[Pd(H2O)2(PPh3)2](CH3SO3)2·2CH2Cl2

“…The IR spectrum of both Ia and IIa shows two broad absorptions at 3508, 3445 cm À1 and 3534, 3489 cm À1 , respectively, assigned to m as (O-H) and m s (O-H) of the water molecules [13,[22][23][24][25] …”

“…20 h, there was production of 25 g of polymer/g of Pd. 13 C NMR analysis shows average n ¼ 27 and that only keto endgroups CH 3 CH 2 CO-are present. Moreover, catalysis occurs with formation of CO 2 .…”

“…Recently, we extended the studies on the hydroesterification of olefins using the catalytic system based on Pd(AcO) 2 /p-CH 3 C 6 H 4 SO 3 H/PPh 3 originally employed by Drent [9][10][11][12][13][14]. Pd(II)-hydrido and -acyl species were detected by NMR spectroscopy [10].…”

“…Moreover, it has been found that the catalytic activity is significantly enhanced when catalysis is carried out in the presence of a hydride source, such as H 2 O, p-CH 3 C 6 H 4 SO 3 H, H 2 . It has been proposed that of the two widely accepted mechanims (Scheme 1), one via initial formation of a Pd(II)-H species, followed by subsequential insertion of the olefin and of CO, with formation of a Pd(II)-acyl intermediate, which undergoes alkanol attack with production of the ester and regeneration of the Pd(II)-hydride [15,16], and the other one via initial formation of a Pd(II)-COOR species, followed by insertion of the olefin and by protonolysis of the resulting Pd(II)-alkyl intermediate [17][18][19], the first one plays a major role [9,[11][12][13]. Further support to this suggestion came very recently from the catalytic activity of the acyl complex trans-[Pd(COEt)(p-CH 3 C 6 H 4 SO 3 )(PPh 3 ) 2 ], isolated in the course of the methoxycarbonylation of ethene [14].…”

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

“…Methanol was purchased from Baker (purity > 99.5%, 0.01% of water) and Pd(OAc) 2 , Ag(TsO), NEt 3 , PPh 3 and p-toluenesulfonic acid were purchased from Aldrich Chemicals. NEt 3 2 ] complexes were prepared according to the methods reported in the literature [24][25][26][27].…”