Carbonylation and formylation

Hydroformylation promoted by metal compounds is sufficiently extensive to attract annual reviews of work in the field.52,1361 1362 However, Co catalysts form a smaller subset. Of the more established Co catalysts, Co2(CO)8 continues to be well studied. The equilibrium reaction pertinent to hydroformylation (Equation (12)), has been recently reviewed.1363 

The attainment of regio- and enantioselectivity are continuing challenges, which form the basis of investigations of new catalytic systems. For example, novel mixed-metal catalysts such as (CO)2Co(u-CO)(u-HC=CBu)Rh(CO)2 promote the stereospecific synthesis of Z-only BuC (CHO) = CHSiMe2Ph from 1-hexyne and HSiMe2Ph.1364 

A recent example where Co2(CO)8 serves as a precatalyst is in the preparation of linear and branched aldehydes via propylene hydroformylation in supercritical C02 (93-186 bar 66-108 °C). Cyclohexane carbaldehyde is produced from cyclohexene using Co2(CO)8 and an acid RCOOH, or else is successful with another established Co catalyst, Co(OOCR)2, assumed to form in situ in the former case. Oligomerization of aldehydes such as n-butanal is achieved with Co2(CO)6L2 as catalyst (L = CO, PR3).1364 

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Carbonyl and formyl halides CF O, CCIFO, and CCljO are stable gases and are commercially available. CBr O is a liquid and is prepared by the reaction of tetra-bromomethane with concentrated sulfuric acid. The replacement of a halogen atom by hydrogen decreases the molecular stability. Formyl fluoride, CHFO, is usually generated, as needed, by the fluorination of dry formic acid with NaF. CHClO is unstable, and must be prepared in a flow system. The procedure is to pass formic acid vapor over solid PClj immediately before it is to be used. The bromine compound, CHBrO, is very short lived. It has been prepared in the vapor phase by the photolysis of a bromine-formaldehyde mixture. 

The Stable carbonyl and thiocarbonyl halide molecules have been studied by IR as well as Raman spectroscopy. Normal coordinate analyses based on force constants transferred from other molecules (Urey-Bradley type), or from ab initio calculations, have aided in the vibrational assignments. Some of the unstable molecules which have been observed in the microwave have been characterized by infrared spectroscopy. The somewhat lower sensitivity of this method means that long path lengths of the gas may be needed. The identification of the various stable and unstable species in the microwave spectrum is simplified by the fact that the absorption lines are usually well resolved from each other. The widths of the bands in the infrared may make the transient species difficult to detect against the stronger absorptions of the stable side products. IR and Raman spectroscopies do have the advantage that they can be used on solid and liquid samples. Since the bands in a low temperature rare gas matrix have a narrower profile, the infrared spectrum is usually simplified over the room temperature gas phase spectrum. Moreover, the vibrational frequencies are only mildly perturbed by solid state effects. For example, CF Se has not been observed in the vapor phase, yet its vibrational dynamics are known from its matrix isolation spectrum. Table 9 gives the vibrational data for the carbonyl, thiocarbonyl, seleno-carbonyl and formyl halides. 

The structure clearly shows the presence of mutually trans carbonyl and formyl groups, the two being easily distinguished by an Os-C-O angle of... 

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