Palladium(II) Pyrazolyl–Pyridyl Complexes Containing a Sterically Hindered N-Heterocyclic Carbene Moiety for the Suzuki-Miyaura Cross-Coupling Reaction

Cationic palladium complexes stabilized by a tridentate neutral {N,N,C} ligand containing a sterically hindered N-heterocyclic carbene (NHC) moiety have been prepared and characterized. The nature of the anionic counterion in the palladium complex has been varied to get crystals suitable for X-ray diffraction. The square planar structure of one of these complexes along with the axial contribution of the sterically hindered NHC fragment has been confirmed by X-ray analysis. In addition, all the isolated [{j3-N,N,C} PdIICl]+X [X = Cl, PF6, BF4, B(C6H3Cl2)4] ion pairs have been scrutinized as catalysts in the cross-coupling Suzuki-Miyaura reaction between phenylboronic acid and variably substituted halo-aryl acceptors. Selected issues from this series have shown improved catalyst turn-over frequencies (TOFs) with respect to structurally related catalytic systems of the state-of-the-art.