η3‐Allylnickel alkoxides and their use as homogeneous and heterogeneous catalysts for the dimerization of olefins

Abstract

Abstractη3‐Allylnickel alkoxides {η3‐C3H5NiOR}2 (R = Me, Et, i‐Pr, Ph, SiPh3) may be activated by gaseous boron trifluoride (BF3) to give active catalysts for the dimerization of propene in homogeneous phase. In CH2Cl2 at −20 °C catalytic turnover numbers of 5000 mol propene(mol Ni)−1h−1 were measured. The nature of the OR group influences both the catalytic activity and the oligomerization product distribution. The ratio of methylpentenes to dimethylbutenes in the dimer fraction may be controlled by the presence of additional phosphine ligands at the nickel atom.The nickel alkoxide precursor was heterogenized on alumina to give {Al2O3}–O–Ni–(η3‐C3H5). Subsequent activation using gaseous BF3 generates a powerful heterogeneous olefin dimerization catalyst which converts 50 × 103 mol propene (mol Ni)−1 at −10° to −5°C in a batchwise process and 143 × 103 mol propene (mol Ni)−1 continuously to give 75% dimers and 25% higher oligomers. The solvent‐free treatment of oxide supports, e.g. alumina or silica, with gaseous BF3 produces strong ‘solid acids’. The activated hydroxyl groups on the support surface serve as effective anchor sites for organometallic complexes to form heterogenous catalysts. By reaction of Ni(cod)2 with {Al2O3}O(BF3)H or {SiO2}O(BF3)H, η1, η2‐cyclo‐octenylnickel–O fragments may be fixed to the surface. In the absence of halogenated solvents, the resulting catalysts, e.g. {SiO2}O–(BF3)–Ni–(η1, η2‐C8H13), dimerize propene continuously at +5°C at the rate of 800 × 103 mol liquid propene (mol Ni)−1.