P–alkene bidentate ligands: an unusual ligand effect in Pd-catalysed Suzuki reactions

The versatile reagent bis(diphenylphosphino)benzaldehyde was used to prepare a variety of electronically and sterically varied ligands using Wittig or aldol methodology in high yields. Pd-catalysed Suzuki reactions were evaluated using these ligands. The influence of the functional group on the alkene, which is in direct conjugation with the phosphorus centre of the ligand, was visible in the activity profiles of the reactions. In general, the activity and stability of the Pd–ligand system increased as electron deficiency and steric bulk increased at the alkene. Furthermore, the ligands could be used at decreased catalyst loadings with improved yields and did not themselves participate in the reactions as substrates.