Site-Selective Anion Exchange in a Palladophosphorane

Abstract

Reported here are studies on the chemoselective ligand substitution at a palladophosphorane possessing two potential sites of chloride substitution. Ligation of palladium(II) chloride with a tridentate chelating ligand (L, P(N(o-N(2-pyridyl)C₆H₄)₂) results in formation of a complex comprising a d⁸ square planar palladium center supported by a geometrically constrained chlorophosphorane (PdClL superscript Cl). The complex thus formed was studied for ligand substitution reactions of the chloro ligand at Pd and P, respectively. Treatment with phenol resulted in substitution of the chloride at the P center while the chloride of the Pd stayed intact, giving complex PdClL superscript OPh. Relatedly, treatment with AgF provided a compound whose NMR spectra are consistent with formation a P–F containing pallado-phosphorane PdClL superscript F. However, attempt to recrystallize the fluoride complex resulted in a formation of a cationic complex with a fluoride-bridged species instead although the fluoride still resided between the two phosphorus centers. Overall, substitution experiments of this palladophosphorane indicated a preference for P–Cl substitution over Pd–Cl. The driving force for the favor toward the exchange at phosphorus has not been extensively explored, but hypotheses have been made which may entail the concept of hard-soft acid-base chemistry and the strength of the bonds involved.