@article {18679, title = {Nickel (II) complexes of bidentate N-N\&$\#$39;ligands containing mixed pyrazole, pyrimidine and pyridine aromatic rings as catalysts for ethylene polymerisation}, journal = {Journal of Organometallic Chemistry}, volume = {799-800}, year = {2015}, month = {2015-12-15 00:00:00}, pages = {90-98}, publisher = {Elsevier }, 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: 2-pyrazol-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-yl-pyridine (pzpy) and bis(3,5-dimethylpyrazol-1-yl)phenylmethane (bpz*mph). The complexes [NiBr2(pzpm)] (1), [NiBr2(4-Mepzpm)] (2), [NiBr2(4-Brpzpm)] (3), [NiBr2(pz*pm)] (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 (AlEt2Cl), the catalyst systems\ 1-3/MAO showing moderate to high activities up to the temperature of 20\ {\textdegree}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 [PdClMe(pzpm)], [PdClMe(pz*pm)], [PdClMe(pzpy)] and [PdClMe(bpz*mph)], also showed to be inactive in the polymerisation of ethylene, when activated by MAO or AlEt2Cl. Selected samples of polyethylene products were characterised by GPC/SEC,1H and\ 13C 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{\textendash}1.7, with total branching degrees generally varying between 2 and 12\%, melting temperatures from 40 to 120\ {\textdegree}C and crystallinities from 40 to 70\%.

}, keywords = {Ethylene, Nickel(II) complexes, Polymerisation, Pyrazole, Pyridine, Pyrimidine}, issn = {0022-328X}, doi = {0.1016/j.jorganchem.2015.09.004}, author = {Moreno-Lara, B. and Carabineiro, S. A. and Krishnamoorthy, P. and Rodr{\'\i}guez, A. M. and Mano, J. F. and Manzano, B. R. and Jal{\'o}n, F. A. and Gomes, P. T.} }