Insertion of alkenyl sulfides into a palladium-aryl bond .1. Synthesis and evolution of a three-membered thiopalladacycle. X-ray crystal structure of a new tetrameric palladium derivative with bridging (phenylthio)alkyl ligands

A three-membered dimeric (phenylthio)alkylpalladacycle (mixture of diastereoisomers) has been synthesized by Pd-C6F5 addition to the double bond of phenyl vinyl sulfide. The coordination mode of the organic moiety changes slowly in solution from a chelating sigma-kappa S-yl to a bridging mu(sigma-kappa S-yl), and the palladacyclopropane isomerizes to an unusual tetrameric palladium complex; the X-ray crystal structure of this latter derivative has been determined, and it shows that each pair of palladium atoms are linked by either two bridging chlorine atoms or two bridging (phenyltkio)alkyl moieties. The tetramer has four chiral carbon atoms and has Sq symmetry (meso form), showing that the crystals are formed stereospecifically from the diastereomeric mixture of dimers. The decomposition pathways of the palladacyclopropane complex have been analysed. Two main routes have been observed, i.e., (a) 1,2-hydrogen shift and Pd-SR p-elimination, which occurs in refluxing toluene, and (b) hydrolysis of the C-S bond to give an aldehyde and a palladium thiolate, predominant at room temperature in the presence of ligands such as tetrahydrothiophene.