Chloride-Promoted Synthesis of Cis Bis-Chelated Palladium(II) Complexes from Ortho-Mercurated Tricarbonyl(η⁶-arene)chromium Complexes^†

A new method of synthesis of homo- and heteroleptic cis bis-chelated Pd(II) species by a transmetalation reaction of the ortho-mercurated 2-[tricarbonyl(η6-phenyl)chromium]pyridine with a series of bis(μ-chloro) palladacyclic aromatic compounds in the presence of a large excess of the chloride salt [NMe4]Cl is reported. These (CO)3Cr-bound bis-chelated Pd(II) species can be designed for the preparation of enantiopure planar chiral cyclopalladated (η6-arene)Cr(CO)3 complexes. The study of the mechanism of this transmetalation reaction reveals the key role of the excess of chloride salt, which is necessary for the isolation of persistent heteroleptic bis-chelated Pd(II) complexes. This method was further applied to the synthesis of highly enantioenriched (+) and (−) samples of the ortho-chloropalladated 2-[tricarbonyl(η6-phenyl)chromium]pyridine, whose enantiopurity was assessed with the aid of diamagnetic Λ and Δ TRISPHAT salts used as chiral shift 1H NMR agents. The absolute configurations of the two enantioenriched complexes were obtained from the corresponding absolute structures determined by X-ray diffraction analyses. The molecular structures of six new heteroleptic bis-chelated Pd(II) complexes are reported.