Synthesis and characterization of a bidentate chelating diisonitrile ligand with two thioethereal sulfurs in a bridging group and its copper(I), rhodium(I) and palladium(II) complexes

Abstract The diisonitrile ligand (L) has been synthesized in five reaction steps from t-butylbenzene with an overall yield of 73%. The reaction of palladium(II) chloride with L leads to the palladium(II) complex, PdLCl 2 , whereas the rhodium(I) complexes, RhL 2 Cl and RhL 2 BF 4 , and the copper(I) complex, CuL 2 BF 4 , are prepared by ligand exchange reactions. These complexes were investigated by means of mass, infrared, nuclear magnetic resonance (NMR) and electronic spectra, as well as molar conductances. Judging from the molar conductances of the RhL 2 Cl, RhL 2 BF 4 and CuL 2 BF 4 complexes, tetrafluoroborate and chloride anions are ionized in acetonitrile. This is also supported by mass spectral data. The strong band at 2100 cm −1 is assigned to the N  C stretching mode. This band shifts to higher frequency upon metal coordination because of the inductive effect produced by the positive charge of the metal ions. This shift increases with increasing charge on the complex. The methylene proton signals of the benzyl group and the bridging group in the ligand are shifted slightly downfield on formation of the complexes. Since the magnitude of the shift is approximately proportional to the oxidation number in the metal complexes, the oxidation number could be distinguished by proton NMR studies of the methylene groups. These results indicate that the NC group in the ligand serves as a σ-donor and the thioethereal sulfur, in the bridging group is not coordinated to the metal atoms. It is surprising that L does not coordinate through the sulfur atoms rather than the isonitriles, because the S-coordinated form would have a stable five-membered-ring structure and the isonitrile coordination gives a fifteen-membered-ring structure.