N-C cleavage in pincer PNP complexes of palladium

Abstract

Several new N-methylated diarylamine-based PNP pincer ligands have been prepared. The synthesis of these ligands is modular and allows incorporation of a variety of substituants that change the solubility and the stereoelectronic properties of the ligand as well as allow for the introduction of a sensitive 19F NMR spectroscopic probe. The reactions of PN(Me)P ligands with PdX 2 (X = Cl, OAc) initially proceed with formation of an adduct, (PN(Me)P)PdX 2, that may exist in either the neutral or the ionic forms. These adducts are unreactive in the case of PPh 2-bearing ligands, but with the more donating PPr 2i-bearing ligands, the adduct evolves into square planar (PNP)PdX with irreversible loss of MeX. Thus, the feasibility of cleavage of an unstrained N-C bond by Pd II is demonstrated. The N-C cleavage is accelerated by decreasing the solvent polarity. The mechanism may involve either N-C oxidative addition or a nucleophilic attack (external or internal) of X - on the Me group of the N-bound PN(Me)P ligand.