Oxidative addition of a hypervalent transannular sulfur-sulfur bond to a Pd(0) complex: Synthesis and crystal structures of 1,5- dithiacyclooctanepalladium(II) bis(trifluoromethanesulfonate) having phosphine ligands

A hypervalent compound 1,5-bis(trifluoromethylsulfonyloxy)-lλ⁴,5λ⁴- dithiabicyclo[3.3.0]octane (1) oxidatively reacted with Pd₂(dba)₃ (dba = dibenzylidene acetone) in acetonitrile to give a dicationic complex [Pd(dtco)(CH₃CN)₂]-(OTf)₂ (2) (DTCO = 1,5-dithiacyclooctane), in which the DTCO ligand coordinated in cis-chelation to the palladium metal. Acetonitrile in 2 was labile enough to be readily replaced by phosphine ligands to give dicationic DTCO-phosphine palladium complexes of the formula [Pd(dtco)(L)₂](OTf)₂ (3: L = PMe₂Ph; 4: L = PPh₃; 5: L₂ = 1,2- bis(diphenylphosphino)ethane; 6: L₂ = (R)-2,2'-bis(diphenylphosphino)- 1,1'- binaphthyl). Molecular structures of 5 and 6 have been characterized by X- ray analysis, indicating that each of these two complexes consists of a discrete dicationic palladium(II) species [Pd(dtco)L₂]²⁺ and two trifluoromethanesulfonate ions without any cation-anion bonding interaction, and revealing that the DTCO is coordinated to the palladium center as a bidentate ligand and that two phosphorus atoms ultimately coordinated to the metal in cis-fashion.