Nuances in fundamental Suzuki−Miyaura cross-couplings employing [Pd(PPh3)4]: poor reactivity of aryl Iodides at lower temperatures

We have explored fundamental Pd-catalyzed C_sp²− C_sp² Suzuki−Miyaura cross-couplings of aryl iodides (Ar−I) employing “classical” Pd/PPh₃ catalyst systems. Surprisingly, we observed particularly inefficient couplings of these ostensibly reactive electrophiles in a range of conventional solvent mixtures at lower temperatures (∼50 °C), which was in stark contrast to analogous reactions featuring the equivalent aryl bromides. This feature of well-established Pd/PPh₃-mediated Suzuki−Miyaura reactions has received scant attention in the literature. Most significantly, our studies suggest that the inefficient coupling of aryl iodides at lower temperatures derives from the unexpectedly poor turnover of the key on-cycle intermediate <i>trans</i>-[Pd(PPh₃) ₂(Ar)(I)] (or related Pd^II−I species) in the presence of PPh₃.