Palladium–NHC complex

In

Synthesis

The synthesis of Pd-NHC complexes follows the methods used for the synthesis of

The utility of palladium-catalyzed cross-coupling reactions is enhanced by the use of N-heterocyclic carbene ligands. Indeed, Pd-NHC complexes have been proven effective in Suzuki-Miyaura, Negishi, Sonogashira, Kumada-Tamao-Corriu, Hiyama, and Stille cross-coupling. Compared to the corresponding Pd-phosphine catalysts, Pd-NHC catalysts can be faster, exhibit broader substrate scope, all with higher turnover numbers.^[4]

Suzuki-Miyaura cross-coupling

In

The use of NHC-Pd-PEPPSI complexes in Negishi cross-coupling has resulted in high turnover numbers and turnover frequencies.^[7] Additionally, NHC-Pd complexes can be used to couple sp3 centers to sp3 centers in higher yield than their non-NHC Pd analogs.^[8] However, studies of Pd-NHC complexes and their utility in Negishi coupling are currently lacking despite these promising results.^[4]

Sonogashira coupling

Pd-NHC complexes used in Sonogashira cross-coupling effect temperature stability in the complex.^[9] As in other Pd-NHC mediated cross-coupling reactions, the use of Pd-NHC complexes also allow higher turnover numbers than their NHC-free counterparts.^[10] NHC-palladacycles permit copper-free Sonogashira reactions to be carried out.^[11][12]

Heck-Mizoroki coupling

The use of Pd-NHC complexes in Heck-Mizoroki cross-coupling permits the use of cheaper, ample supplies of aryl chloride substrates.^[4] Additionally, the activity and stability of the catalyst in Heck-Mizoroki coupling can be enhanced by adjusting the 1,3 substituents on the imidazole ring.^[13]

References