S-Dealkylation reactions of palladium(II) complexes of some phosphorus-sulphur and arsenic-sulphur chelates

Mono- and bis-chelated palladium(11) complexes of o-methylthiophenyldiphenylphosphine (P-SCH3),* bis(o-methy1thiophenyl)phenylphosphine (CH3S-P-SCH,), and their arsenic analogues, o-methylthiophenyldiphenylarsine (As-SCH,) and bis(o-methy1thiophenyl)phenylarsine (CH3S-As- SCH,), have been synthesized. The mono-chelated compounds Pd(X-SCH3)12 and Pd(CH,S-X- SCH3)12 (X = P or As) undergo S-demethylation in hot dimethylformamide to yield Pd2(X-S)212 and Pd2(CH,S-X-S)212. In the presence of one mole excess of free ligand, the dealkylation reaction affords bis-demethylated products Pd(X-S), and Pd(CH3S-X-S),. A mixed ligand species Pd(CH,S-P-S)(CH3S-As-S) was also isolated. These bis-demethylated compounds react with a variety of alkylating agents, RCH2Y, to give a complex of the original or of a different thioether ligand, of the form Pd(X-SR)Y2 or Pd(CH3S-X-SR)Y2 (R = Et, Bu and p-N02C6H4CH2; Y = halogen). In all complexes of CH3S-X-SCH,, including demethylated products, it is suggested that one thiomethyl residue is not coordinated and that they are essentially four-coordinate and square-planar. All four ligands yield the bis-chelated cation species, [Pd(~helate)~]~+, which were isolated as perchlorate salts. The arsenic chelates alone afford the bis-chelated halides Pd(As-SCH3),Y2 and P~(CH,S-AS-SCH,)~Y~, which are non-electrolytes in non-aqueous solution. This fact is attributed to their undergoing a fast rearrangement to form the mono-chelated species. This was confirmed by conductimetric titrations. Where possible, structures and rearrangements were substantiated by proton magnetic resonance spectroscopy.