No abstract

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.

The selective ortho mercuration of tricarbonylchromium derivatives of 2-phenylpyridine, N,N-dimethylbenzylamine, (1S)-1-(dimethylamino)-1-phenylethane, and 2-phenyl-2-oxazoline by Hg(OAc) 2 is reported. The mercurations of the latter (η 6 -arene)Cr(CO) 3 complexes bearing an endogenous ligand have been carried out in soft conditions with yields ranging from 13 to 83%. The optically active complex of (1S)-1-(dimethylamino)-1-phenylethane was stereoselectively orthomercurated. The conversion of the chloromercurated complexes, e.g. (η 6 -Ar-HgX)Cr(CO) 3 , into the corresponding homoleptic trinuclear [(η 6 -Ar)Cr(CO) 3 ] 2 Hg complexes was readily carried out by reaction with Me 4 NCl in boiling acetone. In almost all cases, the so-called symmetrization reaction afforded a mixture of two diastereomers, except for the derivative of (1S)-1-(dimethylamino)-1-phenylethane, which afforded a unique "symmetrized" product. This result suggests that the "symmetrization" reaction occurred with retention of the configuration of the mercury-bound ipso carbon atom. The trimetallic and bimetallic mercurated (η 6 -arene)Cr(CO) 3 complexes were readily converted into cyclopalladated binuclear complexes upon transmetalation with Pd(II) salts. The structures of two orthomercurated compounds and two ortho-palladated complexes are reported.

The reaction of racemic orthomercurated (η6-arene)tricarbonylchromium complexes with bis[(?6-cymene)ruthenium(II)dichloride] affords the corresponding dinuclear (Cr,Ru) products with moderate yields, which have been satisfactorily characterized by X-ray diffraction analysis. The synthesis of nonracemic orthomercurated (η6-arene)tricarbonylchromium complexes has been attempted starting from enantio-enriched homo- and heteroleptic Pd(II) bischelated complexes. Both enantiomers of ortho-mercurated 2-[tricarbonyl(?6-phenyl)chromium]pyridine have been synthesized by reaction of a heteroleptic Pd(II) bischelated with HgCl2. The two mercury(II) complexes were also submitted to a transmetalation reaction with bis[(?6-cymene)ruthenium(II)dichloride] and yielded the corresponding nonracemic (Cr, Ru) products, with enantiomeric excesses ranging from 82 to 89% as suggested by 1H NMR analyses in the presence of BINPHAT anion