Nickel dithiolene complexes as a source of a new family of S,S-dinegative chiral ligands R4btimdt = 5,5′-bis(1,3-dialkyl-4-imidazolidine-2-thione-4-thiolate)

The reaction of the complex [Ni(Bu2timdt)2] (Bu2timdt = −1 charged 1,3-dibutylimidazolidine-2,4,5-trithione) with polyfunctional phosphines: tp [tp = bis(2-diphenylphosphinophenyl)phenylphosphine] and qp [qp = tris(2-diphenylphosphinophenyl)phosphine] produces [Ni(tp)(Bu4btimdt)] (1) and [Ni(qp)(Bu4btimdt)] (2), respectively. X-Ray crystallographic studies show that in both complexes, the nickel ion is coordinated in a trigonal bipyramidal geometry with three P-atoms of the tp and of qp (one of the ‘arms’ of qp is non-coordinating) ligands occupying three facial sites and with two sulfur atoms of Bu4btimdt [5,5′-bis(1,3-dibutyl-4-imidazolidine-2-thione-4-thiolate)]. This new S,S dinegative chelating ligand is generated in situ by desulfurisation of one of the two vicinal sulfur atoms on each ligand in [Ni(Bu2timdt)2] and C–C coupling between the two imidazole rings. The Bu4btimdt anion is chiral, as free rotation about the C–C bond between the two imidazole rings is hindered by high energy barriers. No desulfurisation is observed when reacting Bu4N[Ni(dmit)2] with tp, and the obtained product is [Ni(tp)(dmit)] (3), a nickel complex where the metal is still coordinated with a trigonal bipyramidal geometry (three P-atoms of the tp ligand and two sulfur atoms of the dmit ligand).