Metathesis or Isomerization: Counteranion Directed Reactivity of Grubbs I

Catalytic isomerization of alkenes has garnered interest
for many
years, but there are remaining challenges when it comes to thermodynamic
selectivity and uncontrolled isomerization. Nonbiased substrates,
be it sterically or thermodynamically, remain challenging for many
catalysts, with a few examples available in the more modern literature.
Herein, we present the controlled isomerization of linear alkenes
with a cocatalytic mixture of commercially available catalyst and
reagents: Grubbs I, tris(pentafluorophenyl)borane, and triethylsilane.
DFT calculations indicate that an observed alkylidyne hydride intermediate
is in rapid equilibrium with an alkylidene that binds the alkene substrate.
This combination results in a π-acidic metal and a hydridic
H–B(C6F5)3– counteranion to provide the controlled monoisomerization of aliphatic
alkenes.