Homogeneous hydroformylation of ethylene catalyzed by Rh 4(CO) 12. The application of BTEM to identify a new class of rhodium carbonyl spectra: RCORh(CO) 3(π-C 2H 4)

Abstract

The homogeneous rhodium-catalyzed hydroformylation of ethylene was studied, starting with Rh 4(CO) 12 in n-hexane solvent. The organometallic intermediates and the organic products were measured under isobaric and isothermal conditions using in situ high-pressure infrared spectroscopy. The newly developed algorithm of band-target entropy minimization (BTEM) was applied for the spectral reconstruction to the semibatch data. The classic acyl complex RCORh-(CO) 4 was observed, as well as a new metal carbonyl spectrum. Aldehyde and ketone were observed as organic products. The new organometallic spectrum possesses an acyl band and three strong terminal carbonyl vibrations. The new spectrum was most pronounced at very high ethylene concentrations. Although some very minor vibrations are also apparent, the spectrum is consistent with a trigonal bipyramid structure RCORh(CO) 3L (L = C 2H 4). Given the presence of the ketone formed and the small vibrational intensity at ca. 1725 cm -1 in the new spectrum, the presence of some observable RCOCH 2CH 2Rh(CO) 3L (L = C 2H 4) cannot be excluded.