MECHANISM OF FORMATION OF HETEROLEPTIC NICKEL(II)-ARSINE COMPLEXES FROM HOMOLEPTIC PRECURSORS

The reaction of square-pyramidal [Ni(bdmma)(2)](2+) {bdmma = bis[2-(di methylarsino)phenyl]methylarsine} with either free pdma [o-phenylenebi s(dimethylarsine)] or square-planar [Ni(pdma)(2)](2+) gave five-co-ord inate [Ni(bdmma)(pdma)](2+). Kinetic studies (acidified 5% aqueous ace tonitrile, 25.0 degrees C, I = 0.30 mol dm(-3), LiClO4) showed that th ese processes involve the slow (t(1/2) = 105 min) partial unravelling of a bdmma ligand from [Ni(bdmma)(2)](2+), followed by rapid ligand re organization. The similar rearrangement involving [Ni(bdmma)(2)](2+) a nd square-planar [Ni(tfpdma)(2)](2+) [tfpdma = o-tetrafludorophenylene bis(dimethylarsine)] displays identical kinetic behaviour. In this med ium the sequential addition of two pdma ligands to solvated nickel(II) to produce [Ni(pdma)(2)](2+) has second-order rate constants k(1) = 6 80 and k(2) = 210 dm(3) mol(-1) s(-1) respectively at 25.0 degrees C.