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)

Abstract

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).