What Makes for a Bad Catalytic Cycle? A Theoretical Study on the Suzuki−Miyaura Reaction within the Energetic Span Model

The Suzuki−Miyaura cross-coupling reaction using PMe 3, PPh 3, and P t Bu 3 as ligands was studied theoretically with accurate density functional theory (DFT) methods and the Energetic Span Model. The energetic span model is a tool to compute catalytic turnover frequencies (TOF) from computationally obtained energy states. In this work the model is expanded to include turnover numbers (TON) and off-cycle intermediates. The results show that although the monophosphine route is the fastest pathway, the diphosphine cis route (accessible for small ligands) may also be reactive. The death sentence of the PMe 3 catalyst is the possibility to reach the low energy trans diphosphine species, which substantially reduces the TON. In the PPh 3 case, the formation of Pd 0 L 3 was found to be the major drawback for efficient catalysis. The P t Bu 3 system is the most efficient of the three, as only the monophosphine mechanism is accessible.