Pyrazolate-based dinuclear alpha-diimine-type palladium(II) and nickel(II) complexes - a bimetallic approach in olefin polymerisation

Abstract

A series of compartmental pyrazole/imine, ligands HL1-HL4 have been prepared with different backbone substitutents and different steric bulk of the appending arylimine groups, and two of them have been structurally characterised. With PdCl2 all ligands form the anticipated pyrazolate-bridged bimetallic complexes LPd2Cl3 (1a - 4a) that feature square-planar metal ions, as is confirmed by the X-ray crystallographic analyses of (LPd2C)-Pd-1'l(3) (1a) and (LPd2Cl3)-Pd-3 (3a). With NiBr2(dme), however, oligonuclear systems [LNi2Br3](x) (1b-4b) are formed according, to mass spectrometric findings, which is corroborated by the crystallographic structure of [(LNi2Br3)-Ni-3](3), Complexes 1a-4a can be described as bimetallic versions of Brookhart-type alpha-diimine palladium complexes, where dissociation into mononuclear species is prevented by the dinucleating scaffold and