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 Rh4(CO)12 in n-hexane solvent, at 293 K under 1.0–4.0 MPa CO, 0.5–2.0 MPa H2 and 0.5–5.0 MPa C2H4. The analytic method was in situ high-pressure infrared spectroscopy. Two different metal carbonyl spectra were observed during the course of the active hydroformylations. One spectrum, 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 pressures, has absorbance maxima at 2089, 2038 and 2017 cm−1. It is tentatively suggested that the latter spectrum may belong to the elusive ethyl rhodium tetracarbonyl.