DIMERIZATION OF ETHYLENE CATALYZED BY BETA-DIKETONATE COMPLEXES OF COBALT AND NICKEL

The M(acac)n-Rx Al2Cl6-x (M = Co, n = 2 or 3; Ni, n = 2; R = Et, i-Bu) system, both in the presence and absence of additives, is used for the dimerization of ethylene to a mixture of olenns consisting predominantly of 2-butenes. With the Co(acac)3-Al(i-Bu)3 system, a maximum conversion of 76% with selectivity to 2-butenes of 98 is achieved at 25 °C and 8 kg cm-2 ethylene pressure. Selectivity to 2-butenes is higher with the Co(III) complex compared to Co(II) in combination with trialkylaluminum. However, the three-component Co(acac)2-Et2AlCl-PR3 system is superior to Co(acac)3-Et2AlCl-PR3 for the dimerization of ethylene to 2-butenes. The activity of Co(R1COCHCOR2)2 in combination with alkylaluminum cocatalysts decreases when R1, R2 in the complex are Ph, Ph > CH3, CH3 > Ph, CH3 > CF3, CF3 for AlEt3 and CF3, CF3 > Ph, Ph > Ph, CH3 > CH3, CH3 for Et3Al2Cl3. For Ni(acac)2-Et2AlCl-PR3, the selectivity to 2-butenes decreased in the following order for PR3: P(n-Bu)3 ≈ DIPHOS > PPh3 > P(OPh)3. The effects of ethylene pressure and reaction temperature on the activity and selectivity to 2-butenes are also investigated. © 1990.