Effect of Carboxylate Ligands on Alkane Dehydrogenation
with (<sup><i>dm</i></sup>Phebox)Ir Complexes
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Abstract
A series
of carboxylate-ligated iridium complexes (<sup><i>dm</i></sup>Phebox)Ir(O<sub>2</sub>CR)<sub>2</sub>(H<sub>2</sub>O) (R =
−CH<sub>3</sub>, −CH<sub>2</sub>CH<sub>3</sub>, −CMe<sub>3</sub>, −CH<sub>2</sub>C<sub>6</sub>H<sub>5</sub>, and −CHCMe<sub>2</sub>) were designed and
synthesized to understand the carboxylate ligand effects on the reactivity
of the complex for alkane dehydrogenation. Kinetic studies showed
that the different R groups of the carboxylate iridium complexes can
affect the reactivity with octane in the β-H elimination step.
The rate constants for octene formation with different carboxylate
ligands follow the order R = −CHCMe<sub>2</sub> >
−CMe<sub>3</sub> > −CH<sub>2</sub>CH<sub>3</sub> >
−CH<sub>3</sub> > −CH<sub>2</sub>C<sub>6</sub>H<sub>5</sub>. In contrast,
there is no significant effect of carboxylate ligand on the rate of
the C–H activation step at 160 °C. These experimental
results support the findings in the previously reported density functional
theory study of the (<sup><i>dm</i></sup>Phebox)Ir complex
in alkane C–H activation
