Metal–ligand cooperation and synergistic palladium catalysis for the dual ligand system [2,2′-bipyridin]-6(1H)–one/PCy3: milder conditions for the undirected C–H arylation of arenes

Abstract

The use of Pd(OAc)₂ and a mixture of the cooperating ligand [2,2′-bipyridin]-6(1H)–one (bipy-6-OH) and PCy₃ in an optimal mol ratio of Pd/bipy-6-OH/PCy₃ = 1 : 0.5 : 1 leads to a more active system for the non-chelate-assisted direct arylation of simple arenes. The system operates at a temperature 30 °C lower than that for the Pd/bipy-6-OH system, and it is active for aryl chlorides as arylating partners. Mechanistic experiments support the operation of a bimetallic pathway via two connected catalytic cycles: a Pd/PCy₃ system responsible for the oxidative addition and reductive elimination steps and a Pd/bipy-6-OH system that enables C–H activation. Both cycles are connected by a transmetalation step. The phosphine ligand is not directly involved in the C–H activation, but compared to the monoligand system, the occurrence of the bimetallic route changes the nature of the key intermediate species in the C–H activation, favoring this turnover limiting step and the overall reaction rate.