75108-70-2Relevant academic research and scientific papers
Photolysis and photoinduced isomerization of cis-trans diethylbus(tertiary phosphine)palladium(II)
Ozawa, Fumlyuki
, p. 1481 - 1485 (2008/10/08)
The photolysis of dialkylpalladium phosphine compleses has been investigated. In contrast to the thermal
Mechanisms of Thermal Decomposition of trans and cis-Dialkylbis-(tertiary phosphine)palladium (II). Reductive Elimination and trans to cis Isomerization
Ozawa, Fumiyuki,Ito, Takashi,Nakamura, Yoshiyuki,Yamamoto, Akio
, p. 1868 - 1880 (2007/10/02)
Series of trans- and cis-dialkylpalladium(II) complexes having tertiary phosphine ligands (L) of various basicities and bulkiness have been prepared and their thermolysis and isomerization mechanisms in solution have been studied.Examination of the cause of selective formation of cis-dialkyl isomers by using alkyllithium revealed a new type of trans to cis isomerization promoted by the alkyllithium.A process involving the formation of a trialkylpalladate intermediate is proposed as a mechanism for the trans to cis isomerization.Evidence to support the mechanism has been obtained by experiments using LiCD3.Thermolysis of cis-PdR2L2 has been demonstrated to proceed through a unimolecular process initiated by a rate-determining dissociation of L to produce a three-coordinate cis-PdR2L which reductively eliminates the R groups.Addition of free ligand to the system containing cis-PdMe2L2 effectively blocks the reductive elimination pathway thus forcing the complex to be thermolyzed by a route involving liberation of methane.The second, novel type of trans to cis isomerization reaction proceeding via an intermolecular methyl transfer process has been discovered.As the crucial intermediate in the process a methyl-bridged complex formed between the partly dissociated three-coordinate species and undissociated complex has been postulated.Thermolysis of trans-PdMe2L2 has been found to proceed via initial isomerization to the cis form followed by reductive elimination.The trans-cis isomerization equilibrium greatly favors the cis form for complexes having phenyl-substituted phosphines.For the PEt3-coordinated palladium dimethyl, however, an equilibrium trans/cis ratio of 1.2 is reached at 39 deg C.Factors influencing the stability of the palladium alkyls having the tertiary phosphine ligand are discussed on the basis of present results as well as comparison of the thermolysis behavior of trans-PdEt2L2 and other transition metal alkyls.The presence of an energy barrier between the dissociated T-shaped intermediates trans-PdMe2L and cis-PdMe2L has been assumed.A unimolecular reductive elimination pathway proceeding from T-shaped cis-PdMe2L intermediate through a Y-shaped transition state consistently accounts for the thermolysis as well as isomerization behavior of the trans- and cis-PdMe2L2.
Mechanism of Thermal Decomposition of trans-Diethylbis(tertiary phosphine)palladium(II). Steric Effects of Tertiary Phosphine Ligands on the Stability of Diethylpalladium Complexes
Ozawa, Fumiyuki,Ito, Takashi,Yamamoto, Akio
, p. 6457 - 6463 (2007/10/02)
trans- with a series of alkyl groups and tertiary phosphine ligands of various steric bulkiness (R' = Et, PR3 = PMe2Ph (1), PEt3 (2), PEt2Ph (3), PmePh2 (4), PEtPh2 (5); R'= Pr (6), Bu (7), PR3 = PMe2Ph) are thermolyzed in solution by β-elimination processes liberating alkane and alkene in a 1:1 ratio.Kinetic studies on thermolysis of trans- revealed that they decompose obeying the first-order rate law with respect to the concentration of the palladium complexes.Thermolysis predominantly proceeds from the four-coordinated complex without dissociation of the tertiary phosphine ligand.The minor parallel thermolysis pathway involving the dissociation of the phosphine is completely blocked by addition of the phosphine.Activation enthalpies for thermolysis of the ethylpalladium complexes having various steric bulkiness were virtually constant in the range of 26.0 +/- 1.0 kcal/mol whereas activation entropies showed considerable variation with increasing bulkiness of the phosphine.Thermolysis of trans- (8) cleanly liberated CH2=CD2 and CH2DCD3 with a small isotope effect (kH/kD = 1.4 +/- 0.1).The kinetic results together with examination of the molecular model suggest that the interaction between the bulky phosphine ligands and the ethyl groups causes the destabilization of the Pd-Et bonds.A thermolysis mechanism consistent with the kinetic result assuming an activation state distorted from the square-planar ground state is proposed.
