Selective Isomerization of 1,5-Cyclooctadiene to 1,4-Cyclooctadiene Catalyzed by Bis(acetylacetonato)nickel-Triethyldialuminum Trichloride-Phosphorus Ligand

Article abstract of DOI:10.1246/bcsj.64.2236

The isomerization of 1,5-cyclooctadiene (1,5-COD) with Ni(acac)₂-Et3Al2Cl3-phosphorus ligand (Ni:Al2:P = 1:10:3) was first examined with varying P ligands in toluene in order to find suitable conditions for the formation of 1,4-COD.The product distribution depended largely on the P ligands.For several phosphites possessing very strong ?-acceptor properties, the main product was 1,4-COD.In particular, the less-bulky bicyclic phosphite, 4-ethyl-2,6,7-trioxa-1-phosphabicyclo<2.2.2>octane (L-3) was very effective and gave 1,4-COD in a high selectivity of 93 percent at 66 percent conversion (1,5-COD/Ni = 500, molar ratio) by employing a low temperature of -30 deg C.However, the reaction stopped before reaching completion because the catalyst was deactivated by the accumulation of 1,4-COD product.The conversion, depending on the 1,5-COD/toluene ratio (volume) rather than the 1,5-COD/Ni ratio, increased with a decrease in the 1,5-COD/toluene ratio and was 66-69 percent at a ratio of 0.19.On the other hand, the catalyst (P: L-3) was much less active for 1,4-COD than for 1,5-COD and was deactivated quickly under the same reaction conditions.This appeared to result in a high selectivity of 1,4-COD in the isomerization of 1,5-COD.The mechanistic implications of the experimental results are discussed.