| Abstract |
This work describes the synthesis and characterisation of Ni(II) complexes of the following neutral bidentate nitrogen ligands containing pyrazole (pz), pyrimidine (pm) and pyridine (py) aromatic rings: 2pyrazol-1-yl-pyrimidine (pzpm), 2-(4-methyl-pyrazol-1-yl)-pyrimidine (4-Mepzpm), 2-(4-bromo-pyrazol-1-yl)-pyrimidine (4-Brpzpm), 2-(3,5-dimethyl-pyrazol-1-yl)-pyrimidine (pz*pm), 2-pyrazol-1-ylpyridine (pzpy) and bis(3,5-dimethylpyrazol-1-yl)phenylmethane (bpz*mph). The complexes [NiBr2(pzpm)] (1), [NiBr2(4-Mepzpm)1 (2), lNiBr(2)(4-Brpzpm)i (3), liBrz(Pz*Pm)i (4), [NiBr2(PzPY)] (5) and [NiBr2(bpz*mph)] (6) were tested as catalysts for ethylene polymerisation, in the presence of the cocatalysts methylaluminoxane (MAO) or diethylaluminium chloride (AlEt2CI), the catalyst systems 1-31 MAO showing moderate to high activities up to the temperature of 20 degrees C only in the presence of MAO, whereas 4-6/MAO revealed to be inactive. Other related Pd(II) complexes, already reported in previous works, such as [PdCIMe(pzpm)1, [PdCIMe(pz*pm)1, [PdCIMe(pzpy)] and [PdCIMe(bpz*mph)1, also showed to be inactive in the polymerisation of ethylene, when activated by MAO or AlEt2CI. Selected samples of polyethylene products were characterised by GPC/SEC, H-1 and C-13 NMR and DSC, showing to be low molecular weight polymers with Mn values ranging from ca. 550 to 1500 g mol(-1) and unusually low dispersities of 1.2-1.7, with total branching degrees generally varying between 2 and 12\%, melting temperatures from 40 to 120 degrees C and crystallinities from 40 to 70\%. (C) 2015 Elsevier By. All rights reserved. |
