The isomerisation of 1,4-diarylbutenes by ruthenium–phosphine complexes

Abstract

The catalytic double-bond migration in 1,4-diarylbutenes and in 2-methyl-1,4-diphenylbutenes by RuCl₂(PPh₃)₃ has been studied. The electronic nature of the substituents X in p-XC₆H₄·CH₂·CHCH·CH₂Ph does not affect the reaction rate; it does, however, affect the ratio of p-XC₆H₄·CH₂·CH₂·CHCHPh : p-XC₆H₄·CHCH·CH₂·CH₂Ph which is >1 for electron-withdrawing and <1 for electron-releasing substituents. The reaction is sensitive to steric effects and to the electronic nature of the aryl ligands in the triarylphosphine moiety of the catalyst. The experimental results support a modified metal hydride → alkylmetal mechanism for the reaction and rule out the formation of π-olefin → allylmetal intermediates.