Palladium catalysts immobilized in thin films of ionic liquid for the direct addition of aniline to styrene

Immobilization of organometallic complexes in thin supported films of ionic liquid has been used to generate a new class of hydroamination catalysts. High activities for the addition of aniline to styrene were obtained with a bi-functional system comprising [Pd(DPPF)](CF₃CO₂)₂ and CF₃SO₃H immobilized in silica supported imidazolium salts. In this environment, the metal complexes are concluded to be enclosed in solvent cages of ion pairs of the ionic liquid. With increasing temperature, the imidazolium cations gain mobility until the solvent cages break down at a specific temperature, which is noticeable as phase transition. At temperatures below the phase transition, the catalytic activity was strongly influenced by the choice of the ionic liquid. At temperatures above the phase transition, the activity for formation of the Markownikoff product was, in contrast, nearly identical with all ionic liquids tested. Under these conditions, also the formation of the anti-Markownikoff product was observed.