A DFT Study of Site-Selectivity in Oxidative Addition Reactions with Pd0 Complexes: The Effect of an Azine Nitrogen and the Use of Different Types of Halogen Atoms in the Substrate

The site-selectivity of Pd-catalyzed reactions of 2,3-dihalopyridines [2,3-dichloropyridine (1), 2,3-dibromopyridine (3) and 2-chloro-3-iodopyridine (2)] has been studied by computing the oxidative addition process using DFT calculations. The activating effect of the azine nitrogen atom on C(2) and C(3) has been obtained by comparison with the corresponding dihalobenzene [1,2-dichlorobenzene (4), 1,2-dibromobenzene (5) and 1-chloro-2-iodobenzene (6)]. The performed calcula-tions involve the use of Pd(PPh3)(2), Pd(BINAP) and Pd(XANTPHOS) as catalysts. The formation of pre-reactive complexes proved to be a very important factor in the determination of the activation energy values. A comparison with the simplified systems Pd(PPH3)(2), Pd(H-BINAP) and Pd(H-XANTPHOS) revealed that care has to be taken when simplified catalyst systems are used for the simulation of the oxidative addition process.