In this review, the first in situ NMR studies of several high-pressure carbonylation reactions are described. Important equilibria associated with phosphine-modified catalysts of the Shell type for the hydroformylation of olefins have recently been measured by high-pressure NMR spectroscopy for the first time. Thermodynamic measurements for the reversible additions of CO and H₂ to the Shell-type catalyst, [Co(CO)₃PBu₃]_2, are reported for solvents of varying polarity. The results with CO indicate that CO addition to the metal center is more important than phosphine displacement when the more basic ligands, such as tri-n-butylphosphine, are used. Cobalt(I) formation resulting from the CO addition is favored by polar solvents. The thermodynamics for hydrogen addition to the tri-n-butylphosphine complex is only slightly more favorable than for the unmodified catalyst, HCo(CO)₄. Other carbonylations investigated by in situ NMR for the first time include the HCo(CO)₄ catalyzed hydrogenation of carbon monoxide in supercritical CO and the HCo(CO)₄ catalyzed homologation of methanol in supercritical CO₂. In addition, a new and easily implemented stirring device that achieves efficient gas-liquid mixing in high-pressure NMR probes is reported.

^†Work Supported by the U. S. Department of Energy, Division of Chemical Sciences, Office of Basic Energy Sciences, under Contract W-31-109-ENG-38