The role of ligand transformations on the performance of phosphite- and phosphinite-based palladium catalysts in the Suzuki reaction

The orthometalated complex [{Pd(mu-Cl){kappa(2)-P, C-P(OC6H2-2,4-Bu-t(2))(OC6H3-2,4-Bu-t(2))(2)}}(2)] reacts with phenylboronic acid hydrate and K2CO3 in dimethylacetamide to give [Pd{kappa(2)-P,C-mu(2)-O-P(O)(C6H2-2,4-Bu-t(2))(C6H3-2,4-Bu-t(2))(DMAc)}]. When the reaction is repeated in dimethylformamide 3,3',5,5'-tetra-tert-butyl-2,2'-biphenol is isolated. Both compounds have been characterized crystallographically. The reaction of palladium dichloride with PiPr(2)(OC6H4-4-Et) in 2-methoxyethanol followed by recrystallization in the presence of ethanol leads to the formation of trans- [PdCl2{PiPr(2)(OEt)}(2)], which was also characterized by crystallography. To determine whether related solvolytic processes have a bearing on catalytic activity, the performance of a range of catalysts with "hydrolyzed" and "nonhydrolyzed" ligands was assessed in the Suzuki coupling of aryl bromides. In some cases it was evident that hydrolysis plays a significant role on the catalytic activity; however, this depends not only on the ligand, but also on the combination of ligand and palladium precursor.