The Role of Ligand Transformations on the Performance of Phosphite- and Phosphinite-Based Palladium Catalysts in the Suzuki Reaction

The orthometalated complex [{Pd(μ-Cl){κ 2 - P, C -P(OC 6 H 2 -2,4- t Bu 2 )(OC 6 H 3 -2,4- t Bu 2 ) 2 }} 2 ] reacts with phenylboronic acid hydrate and K 2 CO 3 in dimethylacetamide to give [Pd{κ 2 - P, C -μ 2 - O -P(O)(C 6 H 2 -2,4- t Bu 2 )(C 6 H 3 -2,4- t Bu 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 P i Pr 2 (OC 6 H 4 -4-Et) in 2-methoxyethanol followed by recrystallization in the presence of ethanol leads to the formation of trans -[PdCl 2 {P i Pr 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.