posted on 2016-12-20, 00:00authored byArghya Deb, Avijit Hazra, Qian Peng, Robert S. Paton, Debabrata Maiti
Directing
group-assisted regioselective C–H olefination
with electronically biased olefins is well studied. However, the incorporation
of unactivated olefins has remained largely unsuccessful. A proper
mechanistic understanding of olefination involving unactivated alkenes
is therefore essential for enhancing their usage in future. In this
Article, detailed experimental and computational mechanistic studies
on palladium catalyzed C–H olefination with unactivated, aliphatic
alkenes are described. The isolation of Pd(II) intermediates is shown
to be effective for elucidating the elementary steps involved in catalytic
olefination. Reaction rate and order determination, control experiments,
isotopic labeling studies, and Hammett analysis have been used to
understand the reaction mechanism. The results from these experimental
studies implicate β-hydride elimination as the rate-determining
step and that a mechanistic switch occurs between cationic and neutral
pathway. Computational studies support this interpretation of the
experimental evidence and are used to uncover the origins of selectivity.