Mechanism insight and scope of PEPPSI-catalyzed cross-coupling reaction between triarylbismuth and arylbromide

Abstract

In this paper we report the first cross-coupling reaction of Ar3Bi with Ar’X mediated by Pd-NHC complexes by keeping the ability of Ar3Bi to transfer the three aryl moieties. Investigations were carried out in order to minimize the quantity of the side product Ar-Ar coming from the conversion of Ar3Bi. The results showed that PEPPSI IPr was a good catalyst precursor. Efforts were focussed on the rule of each additive such as PPh3 and the base. It was notably found that the presence of PPh3 (ratio PEPPSI IPr/PPh3: 1/1) was essential to keep the process efficient. Therefore NHC-Pd-PPh3 has been assumed as being the catalytic species. Under the optimized reaction conditions the concomitant formation of the undesired biaryl side product was restricted to its inherent formation consecutive to the reduction of the catalyst precursor to Pd(0). In a last study, the scope and the limitation of the new catalytic methodology were examined and a large range of unsymmetrical biaryl compounds Ar-Ar’ bearing various substituents from strongly electron-donating to electron-withdrawing ones have been prepared and fully characterized.