Pyridine-2(1H)-thione as a Bifunctional Nucleophile in Reaction with PdII and PtII Aryl Isocyanide Complexes

A method for obtaining C,S-cyclometalated deprotonated diaminocarbene complexes via the addition of a bifunctional N,S-nucleophile's endocyclic nitrogen atom to a coordinated isocyanide has been extended to the reactions with pyridine-2(1H)-thione. The coupling of Pd-II- and Pt-II-bis(arylisocyanide) complexes with pyridine-2(1H)-thione leads to the formation of mononuclear C,S-cyclometalated deprotonated diaminocarbene complexes in 90-96 % yield. The reaction proceeds via the initial coordination of the thione sulfur atom to the metal center followed by the intramolecular nucleophilic addition of the heterocyclic nitrogen atom to the metal-ligated isocyanide carbon. Using an excess of pyridine-2(1H)-thione in this reaction leads to the formation of a mono-C,S-cyclometalated complex with a pendant mercaptopyridine ligand which is involved in the reversible intramolecular nucleophilic addition of the pyridine nitrogen to the isocyano carbon. The obtained complexes were characterized by elemental analysis, mass spectrometry, IR and NMR spectroscopies, and single-crystal X-ray diffraction.