Thermodynamic parameters relevant to the phosphine-modified cobalt hydroformylation reaction arereported. Equilibrium constants for the hydrogenation of Co
2(CO)
6L
2 to yield HCo(CO)
3L
were determinedusing in situ
1H
and 31P NMR spectroscopy bet
ween 75
and 175
C for various solvents
and phosphinelig
ands. Special emphasis
was placed on
n-Bu
3P, as this lig
and is prototypical of the Shell hydroformylationprocess. The resultant van't Hoff plots yield the enthalpy
and entropy change (
H = 7.0 ± 0.4 kcal/mol
and S = 2 ± 1 cal/mol·K) for the case of L =
n-Bu
3P in benzene solvent. These parameters
were foundto be relatively insensitive to changes in the solvent, suggesting that the hydride product is not verypolar. Even for isobutyl alcohol solvent, the resultant enthalpy
and entropy changes (
H = 5.8 ± 0.4kcal/mol
and S = -2 ± 1 cal/mol·K)
were found to be similar to those obtained in benzene
and dioxane.Analysis of the
31P NMR line
widths allo
ws rigorous lo
wer limits to be established for the catalyticallyrelevant Co-Co
and Co-H bond energies in the case of L =
n-Bu
3P (Co-Co
23 kcal/mol
and Co-H
60 kcal/mol) relative to the previously reported values for the case of L = CO (Co-Co = 19 ± 2kcal/mol
and Co-H = 59 ± 1 kcal/mol).