Schiff Bases as Inspirational Motif for the Production of Ni(II) and Pd(II) Coordination and Novel Non‐Symmetric Ni(II)‐POCOP Pincer Complexes

Abstract

The synthesis of Ni(II) and Pd (II) coordination complexes containing Schiff's bases derived from the condensation of 2,4dihydroxybenzaldehyde with 4-chloroaniline (L1) or 3,5-dichloroaniline (L2) is described. The condensation of ligands L1 and L2 with chlorodiisopropylphosphine in the presence of a base produced the corresponding non-symmetric pincer ligands POCOP-1 and POCOP-2 with the unexpected CÀ P bond formation by a hydrophosphorylation of the imine process. The new CÀ P bond formation probably occurring by a Kabachnik-Field mechanism type without the requirement of catalysts or additional reagents. Further treatment of ligands POCOP-1 or POCOP-2 with NiCl 2 afforded the non-symmetric pincer complexes Ni(II)-POCOP-1 and Ni(II)-POCOP-2. The crystal structures of L1, 3, Ni(II)-POCOP-1 and Ni(II)-POCOP-2 were unequivocally determined by single crystal X-ray diffraction studies. In addition, the metal complexes were used as catalysts in Suzuki-Miyaura couplings under microwave irradiation, being the Pd(II) derivatives the best catalysts of the series when compared to their Ni(II) analogues under the same reaction conditions.