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

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 degrees 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.