Mono- and Trinuclear Tripodal Platinum(II) Chelated Complexes Containing a Pyridine/Sulfoxide Based Anchoring Framework

New tripodal ligands 2,4,6-triethyl-1,3,5-tris{[1-(2-pyridinyl)ethenyl]sulfinylmethyl}ben zenes 6, characterized by three pendant chains each containing both sulfoxide and pyridine moieties, were synthesized from the corresponding sulfenic acid and 2-ethynylpyridine. Two diastereomeric mixtures were obtained and separated, one racemic mixture 6a, having a C3 symmetry axis and the other 6b with no symmetry. With the aim of studying the coordination ability of these chelating-N,S type ligands, monobranched racemic [1-(2-pyridinyl)ethenyl]sulfinylbenzene 9 was also synthesized. Upon addition of an equivalent amount of the monochelating ligand 9 or the tripodal species 6a to a CD3CN solution of a platinum(II) complex of the type cis-[PtMe2(Me2SO)2] (Pt1) or trans-[PtMeCl(Me2SO)2] (Pt2), platinum(II) coordination and chelation occurred, as definitively indicated by a sharp change in the 1H NMR spectrum towards the final corresponding chelated platinum(II) species and free dimethyl sulfoxide. The prepared platinum(II) species contain one or three fragments of the type {PtMe2}(10 or 12) and {PtMeCl}(11 or 13) bound to the pyridinyl/sulfinyl skeleton in the coordinating ligands 9 and 6a. All the prepared species were fully characterized by NMR spectroscopy from the connectivities in 2D-COSY, 1H-13C HSQC and phase-sensitive 2D-NOESY spectra which confirm the molecular mechanics calculation predictions.