Evidence for a Cooperative Mechanism Involving Two Palladium(0) Centers in the Oxidative Addition of Iodoarenes

Chemistry European Journal 2018

DOI: 10.1002/chem.201704899 

Oxidative addition of iodoarenes (ArI) to Pd0 ligated by 1‐methyl‐1H‐imidazole (mim) in polar solvents leads to cationic arylpalladium(II) complexes [ArPd(mim)3]+. Kinetic analyses evidence that this reaction is second order with respect to the concentration of Pd0, and a mechanism involving the cooperative intervention of two Pd0 centers has been postulated to explain this finding. This unusual behavior is also observed with other nitrogen‐containing ligands and it is general for iodobenzenes substituted with electron‐donating or weakly electron‐withdrawing groups. In contrast, bromoarenes and electron‐poor iodoarenes display first‐order kinetics with respect to Pd0. Theoretical calculations performed at the density functional theory (DFT) level suggest the existence of mim‐ligated ArI‐Pd0 complexes, in which the iodoarene is bound to the metal in a halogen‐bond‐like fashion. Coordination weakens the C−I bond and facilitates the oxidative insertion of another Pd0 center across this C−I bond. This conceptually novel mechanism, involving the cooperative participation of two distinct metal centers, allows a full explanation of the experimentally observed kinetics.

 

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