Mechanism of formation of heteroleptic nickel(II)–arsine complexes from homoleptic precursors

Abstract

The reaction of square-pyramidal [Ni(bdmma) ₂ ] ²⁺ {bdmma = bis[2-(dimethylarsino)phenyl]methylarsine } with either free pdma [o-phenylenebis(dimethylarsine)] or square-planar [Ni(pdma) ₂ ] ²⁺ gave five-co-ordinate [Ni(bdmma)(pdma)] ²⁺ . Kinetic studies (acidified 5% aqueous acetonitrile, 25.0 °C, I = 0.30 mol dm ^-3 , LiClO ₄ ) showed that these processes involve the slow (t _½ = 105 min) partial unravelling of a bdmma ligand from [Ni(bdmma) ₂ ] ²⁺ , followed by rapid ligand reorganization. The similar rearrangement involving [Ni(bdmma) ₂ ] ²⁺ and square-planar [Ni(tfpdma) ₂ ] ²⁺ [tfpdma = o -tetrafluorophenylenebis(dimethylarsine)] displays identical kinetic behaviour. In this medium the sequential addition of two pdma ligands to solvated nickel(II) to produce [Ni(pdma) ₂ ] ²⁺ has second-order rate constants k ₁ = 680 and k ₂ = 210 dm ³ mol ^-1 s ^-1 respectively at 25.0 °C.