Ligand Effects in Pd-Catalyzed Intermolecular Alkyne Hydroarylations

Abstract

The use of palladium(II) catalysts for the synthesis of aryl alkenes by addition of aromatic C−H bonds to alkynes has received a great interest in the literature. The mechanistic features of the reaction have been largely discussed, but no systematic study has been reported so far, particularly for what concerns the role of ligands. In this work, we performed a detailed theoretical study in order to fill this gap. To this extent, three different systems have been considered, with the aim to emphasize how the steric and electronic metal environment affects the catalytic activity and, most notably, steers the reaction selectivity toward the two main products of single and double alkyne insertion into the aromatic C−H bond. Moreover, given the crucial role of the acid media, two acids have been considered, namely, trifluoroacetic acid and tetrafluoroboric acid, to understand the effect of the acid strength and coordinative power on the competition between the different pathways.

Mechanism of Alkyne Hydroarylation Catalyzed by (P,C)-Cyclometalated Au(III) Complexes

“…Two possible reaction paths were envisioned: the outer-sphere route involving nucleophilic addition of the arene to the π-coordinated alkyne at gold or the inner-sphere route involving C–H activation of the arene followed by migratory insertion (Scheme ). No reaction intermediates could be detected at the time, but the outer-sphere mechanism was inferred indirectly from the stereochemical outcome: ANTI addition of the arene across the CC triple bond.…”