The homogeneous rhodium catalyzed hydroformylation of ethylene starting with tetrarhodium dodecacarbonyl - the observation of a new type of rhodium carbonyl spectrum

The homogeneous rhodium catalyzed hydroformylation of ethylene was studied, starting with Rh-4(CO)(12) in n-hexane solvent, at 293 K under 1.0-4.0 MPa CO, 0.5-2.0 MPa H-2 and 0.5-5.0 MPa C2H4. The analytic method was in situ high-pressure infrared spectroscopy. Two different metal carbonyl spectra w ere observed during the course of the active hydroformylations. One spectru m, observed primarily at high CO partial pressures, corresponds exactly to the well-documented mononuclear acyl rhodium tetracarbonyl(2112, 2068, 2038 , 2020 cm(-1)). The other spectrum, observed primarily at low CO partial pr essures, has absorbance maxima at 2089, 2038 and 2017 cm(-1). It is tentati vely suggested that the latter spectrum may belong to the elusive ethyl rho dium tetracarbonyl. (C) 2000 Elsevier Science B.V. All rights reserved.