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Oxidative CÀ H/CÀ H coupling of arenes were carried out on palladium nitrosyl carboxylates Pd 3 (NO) 2 (CX 3 CO 2 ) 4 (ArH) 2 (I: X = Cl, Ar = Ph; II: X = F, Ar = Tol) under relatively mild conditions (5 bars of O 2 , 110°C, 24 h). Over trifluoroacetate complex II, we obtained higher yields in both homocoupling of benzene and heterocoupling of benzene and other arenes. The catalytic system showed high selectivity over 90 % for all the studied substrates. The DFT calculations on the activation of arene through the proton transfer showed that the activation energies for all possible intramolecular pathways are much higher than those for the proton transfer to free carboxylate ions, indicating that the presence of external base is required to increase the performance of the considered catalytic system. In the catalytic tests it was found that the preferable external bases are ions of strong carboxylic acids, while acetate provides almost negligible improvement and pyridine suppresses the reaction most likely due to binding to active sites on palladium.[a] Dr.

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