A process for the hydroformylation of relatively low volatility alkenes (demonstrated for 1-dodecene) in a continuous flow system is described. The catalyst is dissolved in an ionic liquid while the substrate and gaseous reagents are transported into the reactor dissolved in supercritical CO(2), which simultaneously acts as a transport vector for aldehyde products. Decompression of the fluid mixture downstream yields products which are free of both reaction solvent and catalyst. The use of rhodium complexes of triaryl phosphites leads to ligand degradation through reaction of the ionic liquid with water and subsequent attack of the released HF on the phosphite. Sodium salts of sulfonated phosphines are insufficiently soluble in the ionic liquids to obtain acceptable rates, but replacing the sodium by a cation similar to that derived from the ionic liquid, allows good solubility and activity to be obtained. The nature of the ionic liquid is very important in achieving high rates, with 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amides giving the best activity if the alkyl chain is at least C(8). Catalyst turnover frequencies as high as 500 h(-1) have been observed, with the better rates at higher substrate flow rates. Rhodium leaching into the product stream can be as low as 0.012 ppm, except at low partial pressures of CO/H(2), when it is significantly higher. Oxygen impurities in the CO(2) feed can lead to oxidation of the phosphine giving higher rates, lower selectivities to the linear aldehyde, increased alkene isomerization and greater leaching of rhodium. However, it is found that under certain process conditions, the supercritical fluid-ionic liquid (SCF-IL) system can be operated continuously for several weeks without any visible sign of catalyst degradation. Comparisons with commercial hydroformylation processes are provided.
Two iron complexes, cis-(CO) 4 Fe[C(O)C(O)CH 3 ](CO 2 CH 3 ) (1a) and cis-(CO) 4 Fe[C(O)CO 2 -CH 3 ][C(O)CH 3 ] ( 3), are reported. Each complex can be considered as a γ-keto ester with a metal atom inserted into the chain linking its two organic groups. 1a is the only one found to evolve thermally, similarly to organic γ-keto esters, into the methoxy metallalactone (CO) 4 FeC(O)C(CH 3 )(OCH 3 )OC(O) (2a). This reaction is not reversible and does not require any acid or alkaline catalysis. The process does not result from a spontaneous dissociation of the methoxycarbonyl ligand of 1a but from an associative intra or intermolecular mechanism. A similar process can also be induced by pronucleophile reagents, and it affords a series of substituted metallalactones: (CO) 4 FeC(O)C(CH 3 )(Nu)OC(O) (Nu ) OCH 3 (2a), OC 2 H 5 (2b), SC 2 H 5 (2c), P(C 6 H 5 ) 2 (2d), P(C 6 H 11 ) 2 (2e)). Complex 2e has been characterized structurally. These substituted lactones are formed by nucleophilic attack of the reagent at the pyruvyl β-carbonyl followed by carbonylate attack on the alkoxycarbonyl ligand.
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