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 R at lower temperatures (similar to 50 degrees 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 trans-[Pd(PPh3)(2)(Ar)(I)] (or related Pd-II-I species) in the presence of PPh3.