Pd(η<sup>3</sup>‑1-PhC<sub>3</sub>H<sub>4</sub>)(η<sup>5</sup>‑C<sub>5</sub>H<sub>5</sub>), an Unusually Effective Catalyst Precursor
for Heck–Mizoroki and Sonogashira Cross-Coupling Reactions
Catalyzed by Bis-Phosphine Palladium(0) Compounds
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Abstract
The compound Pd(η<sup>3</sup>-1-PhC<sub>3</sub>H<sub>4</sub>)(η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>) reacts
essentially quantitatively with a variety of phosphines L to form
cross-coupling catalysts of the type PdL<sub>2</sub> and has recently
been shown to be a much more effective catalyst precursor for Suzuki–Miyaura
cross-coupling reactions in comparison to more commonly utilized precursors
such as Pd(PPh<sub>3</sub>)<sub>4</sub>, Pd<sub>2</sub>(dba)<sub>3</sub>, and Pd(OAc)<sub>2</sub>, which do not effectively generate two-coordinate
species PdL<sub>2</sub>. This advantage is expected to apply also
to e.g. Heck-Mizoroki and Sonogashira cross-coupling reactions, both
of which are generally believed to be catalyzed by species of the
type PdL<sub>2</sub>. Therefore, comparisons of the efficacies of
catalyst systems based on Pd(η<sup>3</sup>-1-PhC<sub>3</sub>H<sub>4</sub>)(η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>), Pd(PPh<sub>3</sub>)<sub>4</sub>, Pd<sub>2</sub>(dba)<sub>3</sub>, and Pd(OAc)<sub>2</sub> are made utilizing the conventional coupling reactions of
aryl halides with methyl acrylate and styrene for Heck–Mizoroki
coupling and with phenylacetylene for Sonogashira coupling. As anticipated,
catalyst systems based on Pd(η<sup>3</sup>-1-PhC<sub>3</sub>H<sub>4</sub>)(η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>) are
found to be significantly more active
