Experimental study of the [ZnCl2(THF)2] catalyzed cis/trans-isomerization of [Pd(C6Cl2F3)Me(PPh3)2] and of the transmetalation of trans-[PdCl(C6Cl2F3)(PPh3)2] with [ZnMeCl(THF)2]

Abstract

The kinetics of the transmetalation reaction between trans-[PdCl(C6Cl2F3)(PPh3)2] and [ZnMeCl(THF)2] shows a complex dependence on [PPh3] for the rate of formation of different reaction products: cis and trans-[Pd(C6Cl2F3)Me(PPh3)2], trans-[PdClMe(PPh3)] (which further reacts with [ZnClMe(THF)2]), and [Zn(C6Cl2F3)Cl(THF)2]. To better understand the system the reactions between cis and trans-[Pd(C6Cl2F3)Me(PPh3)2] and [ZnCl2(THF)2] (the retro-transmetalation reactions) and their kinetic dependence on [PPh3] were studied. These reactions lead to the formation of trans-[PdClMe(PPh3)] and [Zn(C6Cl2F3)Cl(THF)2] as main products. Additionally, the experiments show that the isomerization of cis to trans-[Pd(C6Cl2F3)Me(PPh3)2] is catalyzed by [ZnCl2(THF)2]. In this catalyzed isomerization the concentration of PPh3 is involved in two ways: It modulates the concentration of the organozinc [Zn(C6Cl2F3)Cl(THF)2], and also it shifts a ligand substitution equilibrium in the palladium complex, producing an anomalous dependence of the reaction rate on the concentration of triphenylphosphine.