Ligands for Pd catalysed cross-coupling reactions
Acomparison of commercially accessible ligands
In a comparative study, a large variety of commercially available phosphine ligands and types of Pd catalysts was evaluated for Suzuki-Miyaura cross-coupling, the Buchwald-Hartwig amination and Buchwald amidation reactions. Electron rich and sterically demanding phosphine ligands such as Buchwald or cataCXium ligands were found to frequently exhibit improved catalyst performance in those cross-coupling reactions compared to generic ligands. In general the use of catalysts of the type PR3-Pd G3 was found advantageous, particularly with respect to low catalyst loadings and high chemoselectivities. Despite the fact, that exceptions from this tendency could be found, as generic diphosphines matched or even outperformed such ligands, it was demonstrated that these modular and in bulk amounts available ligands are a valuable starting point for rapid and efficient development of C-X cross coupling reactions.
Over the last two decades the field of Pd catalysed C-C and C-X cross coupling reactions has wit-nessed re-mark-able progress, which eventually led to the development of numerous pro-ces-ses on pilot plant or production scale (1). Such advancement came true be-cause of the availability of suitable ligands, the broad evaluation of the scope of the metho-do-logy and the evolution of new ligands and catalyst precursors (2). The dedication of industrial groups to implement such procedures on commercial scale was an additional driving force for further improvement of the state-of-the-art. While a “one-catalyst-fits-all” solution still has to be identified, the fast and efficient evaluation of the most suited ligand/catalyst system is still a major task in the course of process ... ...