Pd–benzothiazol-2-ylidene complex in ionic liquids: Efficient catalyst for carbon–carbon coupling reactions

Pd-benzothiazol-2-ylidene complex 3 catalyzes efficiently the carbon–carbon coupling reactions in the ionic liquid tetrabutylammonium bromide (TBAB) as solvent. The IL does exert a striking influence on the reactivity and the stability of the catalyst. This is probably due to the formation, by reaction with TBAB, of an anionic and more nucleophilic complex surrounded by large tetrabutylammonium cation that would impede, by imposing a Coulombic barrier for collision, the formation of clusters growing further into catalytically inactive metal particles. On the contrary, ionic liquids with planar structures and poor nucleophilic anions like the [bmims], that form tight ion pairs, are barely efficient in influencing the reactivity and stability of the catalyst.