β-X vs. β-H Elimination. Selection Rules for Chemoselectivity Enabled by Mechanistic Studies

Alkylpalladium complexes are important intermediates in several industrially relevant catalytic reactions such as the Mizoroki–Heck, alkyl C–H activation and ethylene polymerisation. Beta-elimination - of either a hydride (β-Η) or a heteroatom (β-Χ) - is the most common decomposition pathway for these intermediates; this can either promote the desired reaction as in the Mizoroki–Heck reaction, or it can hinder reaction progress as in ethylene/vinyl halide co-polymerisations. Despite the importance of these elimination 15 processes, little mechanistic understanding exists with respect to the factors that control them. We present a systematic investigation of the factors governing the competition between β-Η and β-Χ in catalytically relevant alkylpalladium complexes. These results enabled us to derive selection rules which dictate ligand choice to control selectivity for either elimination. This knowledge may allow chemists to manipulate beta-eliminations in the design of chemoselective catalytic reactions for a wide range of applications.