TY - JOUR
T1 - An NMR study on the mechanism of ethene hydromethoxycarbonylation catalyzed by cationic Pd(II)-PPh3 complexes
AU - Amadio, E.
AU - Cavinato, G.
AU - Härter, P.
AU - Toniolo, L.
PY - 2013
Y1 - 2013
N2 - The reactivity of cis-[Pd(H2O)2(PPh3) 2](TsO)2.2(H2O) (I,H2O), trans-[Pd(COEt)(TsO)(PPh3)2] (II) and trans-[Pd(COOMe) (TsO)(PPh3)2] (III) has been studied by 1H and 31P{1H} NMR spectroscopy under conditions that mime the catalytic ethene hydromethoxycarbonylation (EHMC), i.e. in the presence of PPh3, H2O and TsOH. (I,H2O), in the presence of two equivalents of PPh3, reacts with MeOH and CO (0.3 MPa) at 193 K to give [Pd(COOMe)(TsO)(PPh3)3] (III′), which reacts with H2O in the presence of TsOH at 293 K to generate [PdH(PPh 3)3](TsO) (IV) quantitatively. This hydride inserts ethene (0.3 MPa, 293 K) to give trans-[Pd(Et)(TsO)(PPh3)2] (V), which reacts with CO (0.3 MPa, 223 K) giving [Pd(COEt)(PPh3) 3](TsO) (II)′ and initiates the catalytic EHMC at 293 K. II, in combination with PPh3 and TsOH, reacts at 293 K with MeOH with quantitative formation of methyl propanoate (MP) and IV and promotes the catalysis starting from this temperature, under 0.6 MPa of CO/ethene (1/1) when the ratio PPh3/TsOH/II is 2/6/1; upon increasing the PPh 3/II ratio, the catalytic activity passes through a maximum when the ratio is 4/1, even though it initiates at a higher temperature. In the absence of added ligand, MP is formed in a stoichiometric amount, catalysis is not observed and decomposition to Pd metal occurs. Therefore, PPh3 is essential in order to stabilize hydride IV, though an excess of ligand is detrimental. III does not insert ethene even at 343 K, a temperature well above that at which catalysis is observed. All these experimental evidences support the Pd-H cycle.
AB - The reactivity of cis-[Pd(H2O)2(PPh3) 2](TsO)2.2(H2O) (I,H2O), trans-[Pd(COEt)(TsO)(PPh3)2] (II) and trans-[Pd(COOMe) (TsO)(PPh3)2] (III) has been studied by 1H and 31P{1H} NMR spectroscopy under conditions that mime the catalytic ethene hydromethoxycarbonylation (EHMC), i.e. in the presence of PPh3, H2O and TsOH. (I,H2O), in the presence of two equivalents of PPh3, reacts with MeOH and CO (0.3 MPa) at 193 K to give [Pd(COOMe)(TsO)(PPh3)3] (III′), which reacts with H2O in the presence of TsOH at 293 K to generate [PdH(PPh 3)3](TsO) (IV) quantitatively. This hydride inserts ethene (0.3 MPa, 293 K) to give trans-[Pd(Et)(TsO)(PPh3)2] (V), which reacts with CO (0.3 MPa, 223 K) giving [Pd(COEt)(PPh3) 3](TsO) (II)′ and initiates the catalytic EHMC at 293 K. II, in combination with PPh3 and TsOH, reacts at 293 K with MeOH with quantitative formation of methyl propanoate (MP) and IV and promotes the catalysis starting from this temperature, under 0.6 MPa of CO/ethene (1/1) when the ratio PPh3/TsOH/II is 2/6/1; upon increasing the PPh 3/II ratio, the catalytic activity passes through a maximum when the ratio is 4/1, even though it initiates at a higher temperature. In the absence of added ligand, MP is formed in a stoichiometric amount, catalysis is not observed and decomposition to Pd metal occurs. Therefore, PPh3 is essential in order to stabilize hydride IV, though an excess of ligand is detrimental. III does not insert ethene even at 343 K, a temperature well above that at which catalysis is observed. All these experimental evidences support the Pd-H cycle.
KW - Ethene
KW - Hydridopalladium cycle
KW - Hydromethoxycarbonylation
KW - NMR
UR - http://www.scopus.com/inward/record.url?scp=84881523462&partnerID=8YFLogxK
U2 - 10.1016/j.jorganchem.2013.07.043
DO - 10.1016/j.jorganchem.2013.07.043
M3 - Article
AN - SCOPUS:84881523462
SN - 0022-328X
VL - 745-746
SP - 115
EP - 119
JO - Journal of Organometallic Chemistry
JF - Journal of Organometallic Chemistry
ER -