Mechanistically informed selection rules for competing β-hydride and β-heteroatom eliminations

Alkylpalladium complexes are important intermediates in several industrially relevant catalytic reactions, such as the Mizoroki–Heck reaction, alkyl C–H activation and ethylene polymerization. β-elimination—of either a hydride (β-Η) or a heteroatom (β-Χ)—is the most common decomposition pathway for these intermediates; this can either lead to the desired reaction, as in the Mizoroki–Heck reaction, or it can hinder the reaction progress, as in ethylene and/or vinyl halide co-polymerizations. Despite the importance of these elimination processes, little mechanistic understanding exists with respect to the factors that control them. Here we present a systematic investigation of the factors that govern the competition between β-Η and β-Χ in catalytically relevant alkylpalladium complexes. These results enabled us to derive selection rules that dictate ligand choice to control the selectivity for either elimination. This knowledge may allow chemists to manipulate β-eliminations in the design of chemoselective catalytic reactions for a wide range of applications. β-hydride and β-heteroatom eliminations are elementary steps in many catalytic reactions used in the synthesis of drug molecules and polymers. However, the elimination processes often compete leading to unpredictable outcomes. Here, a series of mechanistically informed selection rules are developed to selectively achieve the desired elimination.