Nickel(II) complexes with tripodal NNN ligands as homogenous and supported catalysts for ethylene oligomerization

Four new coordination compounds of nickel (II) with derivatives of N,N-bis(pyrazol-1-ylmethyl)propylamine were synthesized; their composition and structure were confirmed with IR-spectroscopy and elemental analysis. The structures of products 13 and 15 were unambiguously established in an X-ray diffraction study. Compounds 13 and 15 crystallize in the orthorhombic space groups Pna21 and P212121 correspondingly and represent a monomeric octahedral nickel complexes, that are typical for tridentate scorpion-type ligands. New method for immobilization of nickel complexes with derivatives of N,N-bis(pyrazol-1-ylmethyl)propylamine on silica gel modified with aminopropyl groups was proposed. The EXAFS/XANES analysis indicated that Ni atom in the supported complexes adopt almost octahedral geometry, being partly surrounded by nitrogen atoms from organic ligand and partly grafted to silica surface through silanol groups, with Br− in outer coordination sphere. Both the original and the supported complexes, when activated with Et2AlCl or Et3Al2Cl3, catalyze ethylene oligomerization with the predominant formation of butene isomers. Generally, the immobilized complexes show higher activity and better selectivity towards 1-butene formation.