Reactions of cyclopalladated compounds. Part 21. Various examples of sulphur-assisted intramolecular palladation of aryl and alkyl groups

Abstract

The cyclopalladation reactions of several sulphur-containing ligands have been investigated. The thioethers benzyl methyl sulphide, methyl naphthyl sulphide, 2,6-dimethylphenyl methyl sulphide, and neopentyl phenyl sulphide have been metallated by palladium acetate in acetic acid at either aryl or alkyl carbon atoms to afford, after reaction with lithium chloride in acetone, dimeric chloride bridged cyclopalladated complexes in moderate (22%) to good (81%)yields. In these products each metal is part of a five-membered ring. The same reaction with 2-biphenyl methyl sulphide afforded a dimeric complex containing a six-membered cyclopalladated ring through palladation of the ortho position of the biphenyl group. 4,4′- Dimethoxythiobenzophenone and N,N,N′,N′-tetramethyl-thiourea have been palladated by using a ligand-exchange reaction with [{[graphic omitted]Me₂-2)Cl}₂] in the presence of stoicheiometric amounts of trifluoroacetic acid. This afforded good yields of dimeric palladocyclic complexes through the metallation of a carbon ortho to the thioketone, or of a methyl group of the thiourea respectively. With 1,3-bis(methylthiomethyl)benzene this latter reaction, by metallation of the 2 position of the aryl ring, afforded excellent yields of a monomeric compound in which both sulphur atoms are co-ordinated to the palladium centre.