Synthesis of nickel(II) complexes containing neutral N,N− and anionic N,O− bidentate ligands, and their behaviour as chain-growth catalysts; structural characterisation of complexes containing (mim)2CO, mimCO2-, and mimCPh2O− (mim = 1-methylimidazol-2-yl)

The complexes NiBr2(L2) [L2 = (mim)2CO (7a), (bim)2CO (7b), py(mim)CO (8), PhNCHbim (9)], NiBr(o-Tol){(mim)2CO} (10), Ni(L2)(o-Tol)(PPh3) [L2=mimCO2-(11a),bmCO2-(11b), mimCPh2O− (12), mimC6H4O− (13)], and [Ni{(mim)2CO}3][BF4]2 · 0.25H2O (16) have been synthesised from nickel(II) salts (7–9, 16) or NiBr(o-Tol)(PPh3)2 [10–13], where mim = 1-methylimidazol-2-yl, bim = 1-benzylimidazol-2-yl, and py = pyridin-2-yl. The square-planar complexes (11a, 12) and octahedral 16 have been characterised by X-ray diffraction studies, together with octahedral cis-[Ni{(mim)2CO}2Br(OH2)]Br · CD3CN (14) and cis-[Ni{(mim)2CO}2(OH2)2]Br2 · 3CD3CN (15). Preliminary catalytic studies have been undertaken with a number of the nickel complexes. Complexes 11–13 form single component catalysts for the oligomerization or polymerization of ethylene and the bromo-complexes (7–9) form active catalysts for the oligomerization or polymerization of ethylene when activated with MMAO.

Graphical abstractSquare-planar complexes of formulation NiBr2(N–N), NiBr(o-Tol)(N–N), and Ni(N–O)(o-Tol)(PPh3) (where bidentate N–N and [N–O]− ligands contain at least one N-alkylimidazole donor and the oxygen donor is a carboxylato, alkyloxo or aryloxo group) have been synthesised and examined as catalysts for oligomerisation or polymerisation of ethylene. X-ray structural studies are reported for Ni(mimCO2)(o-Tol)(PPh3), Ni(mimCPh2O)(o-Tol)(PPh3), cis-[Ni{(mim)2CO}2Br(OH2)]Br · CD3CN, cis-[Ni{(mim)2CO}2(OH2)2]Br2 · 2CD3CN, and [Ni{(mim)2CO}3][BF4]2 · 0.25H2O (mim = 1-methylimidazol-2-yl).Figure optionsDownload full-size imageDownload as PowerPoint slide