Novel ditopic organic ligands containing the terpyridine and 2-thiohydantoin fragments

Organic ligands containing two dissimilar chelating fragments are of interest for the preparation of homo and heteropolynuclear metal complexes. Such metal complex es with ligands having electron donating conjugated sys tems are attractive because of their special photochemical (absorption and emission) properties.1 Continuing our in vestigations into the synthesis of terpyridines,2,3 thio hydantoins,4,5 and their coordination compounds, we ob tained novel organic ligands 1 and 2 combining both the aforementioned structural units and studied their methyla tion with MeI and complexation reactions of compound 2 with CoII and RhIII chlorides (Scheme 1). For the synthesis of terpyridine containing (tpy) 2 thio hydantoins, we employed two alternative approaches: con densation of 4 ́ (4 formylphenyl) [2,2 ́:6 ́,2]terpyridine with N(3) substituted 2 thiohydantoins (A) and three component condensation of 4 ́ (4 formylphenyl) [2,2 ́:6 ́,2]terpyridine with isothiocyanate and glycine (B) (the latter approach was used only to obtain N(3) phenyl derivative 2). Thiohydantoins 1 and 2 were alkylated with iodo methane to give 2 methylthio 3,5 dihydro 4H imidazol 4 ones 3 and 4, which are also of interest as potential ligands in complexation reactions. The Z configuration of the exocyclic C=C bond in compounds 1—4 was deter mined from the chemical shifts of the signals for the vinyl ic protons in the 1H NMR spectra.6 Reactions of ligand 2 with cobalt and rhodium chlo rides gave polynuclear complexes 5 and 6, which were identified by IR spectroscopy, elemental analysis, and mass spectrometry. The shift of the absorption band of the C=O group in the IR spectra of compounds 3—6 by 15—35 cm–1 to the lower wavenumbers (compared to its position in the spectra of thiohydantoins 1 and 2) suggests that the carbo nyl group is involved the system of conjugated  bonds. Plausible structures of complexes 5 and 6 are shown in Scheme 1. However, X ray diffraction is required to de termine their true structures. To sum up, we synthesized a novel type of ditopic organic ligands in which chelating fragments differ in ba sicity. Such a combination of electron donating centers (sulfur is a soft base of medium strength, while nitrogen is a harder and stronger base7,8) has not been document ed earlier. The ligands obtained seem to be promising for subsequent preparation of complexes of dissimilar metal ions.