| Autor: |
White, S., Bennett, B. L., Roddick, D. M. |
| Zdroj: |
Organometallics; June 21, 1999, Vol. 18 Issue: 13 p2536-2542, 7p |
| Abstrakt: |
Catalytic ethylene dimerization by (dfepe)Pt(Me)X complexes in aprotic and trifluoroacetic acid solvents is described. In CH2Cl2, catalyst deactivation due to acid loss and generation of (dfepe)Pt(η2-C2H4) is observed. In contrast, long-term ethylene dimerization activity takes place in trifluoroacetic acid at 80 °C and produces 2-(trifluoroacetato)butane as the sole organic product. Under these reaction conditions, the catalyst resting state is (dfepe)Pt(Et)(O2CCF3). At 20 °C, reversible acid elimination from (dfepe)Pt(Et)(O2CCF3) and ethylene ligand exchange results in catalytic vinylic H+/D+ exchange with CF3CO2D (t1/2 ≈ 40 min). Analogous palladium systems exhibit enhanced dimerization activity at 25 °C (340 turnovers/h, 100 psi C2H4) and form (dfepe)2Pd as a catalyst resting state. Inhibition of catalytic activity in the presence of added dfepe was noted. Comparisons between catalytic runs in CF3CO2H and CF3CO2D gave an apparent solvent kinetic effect of 3.5(2), based on an initial second-order rate dependence on ethylene. In CF3CO2D, regioselective acid addition to give only CH3CH(O2CCF3)CH(D)CH3 indicates that isomerization to 2-butene has occurred prior to 1,2-acid addition. A general olefin dimerization mechanism incorporating protonation preequilibria is presented. |
| Databáze: |
Supplemental Index |
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