Behavior of dicobaltoctacarbonyl in the hydroformylation of 1-hexene in polar solvents under variable carbon monoxide and hydrogen pressure.
The influence of electron donating properties of polar solvents on the rate of 1-hexene hydroformylation at 373 K and 100 bar and the duration of the catalysis initialization (In) phase indicated a high complex stability of Co(solvent)62+ species for e.g., CH3CN, DMF, and pyridine, however, only a small catalytic activity for the latter 2 compared to the Co(CH3CN)62+ complex. The duration of the In phase induced by dis- and comproportionation of Co2(CO)8 prior to the start of the reaction was polarog. studied and showed correlation with the half-wave potentials of the Co-solvent complex cations. Variation of the molar H/CO ratio showed increases of the In period for values up to 1.5 as a consequence of predominantly occurring comproportionation followed by a decrease for larger values indicating control by disproportionation. A reaction mechanism is given in which the In phase, the transition from the In to the catalysis phase, and the catalysis cycle is considered, together with occurring cationic and anionic catalyst species.
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