Rhodium hydroformylation catalysts phosphine modified

The catalysts used in hydroformylation are typically organometallic complexes. Cobalt-based catalysts dominated hydroformylation until 1970s thereafter rhodium-based catalysts were commerciahzed. Synthesized aldehydes are typical intermediates for chemical industry [5]. A typical hydroformylation catalyst is modified with a ligand, e.g., tiiphenylphoshine. In recent years, a lot of effort has been put on the ligand chemistry in order to find new ligands for tailored processes [7-9]. In the present study, phosphine-based rhodium catalysts were used for hydroformylation of 1-butene. Despite intensive research on hydroformylation in the last 50 years, both the reaction mechanisms and kinetics are not in the most cases clear. Both associative and dissociative mechanisms have been proposed [5-6]. The discrepancies in mechanistic speculations have also led to a variety of rate equations for hydroformylation processes. 

Hydroformylation of 2,6-dimethyl-6-hepten-2-ol produces hydroxycitronellal (equation 12).22 Subjecting allyl alcohol to hydroformylation reaction conditions with HCo(CO>4 yields only propanal, isomerization taking place more rapidly than hydroformylation.2 Phosphine-modified rhodium catalysts will convert allyl alcohol to butane-1,4-diol under mild conditions in the presence of excess phosphine, however (equation 13).5 30 31 When isomerization is blocked, hydroformylation proceeds normally (equation 14). An elegant synthesis of the Prelog-Djerassi lactone has been accomplished starting with the hydroformylation of an allylic alcohol (equation IS).32... 

Koch and Leitner extended this work in a comprehensive study (227,228) comparing the hydroformylation of 1-octene using a rhodium complex catalyst without modifiers and with both phosphine and phosphite ligands. They report that SCCO2 is a generally applicable reaction medium for highly efficient... 

Rhodium Ca.ta.lysts. Rhodium carbonyl catalysts for olefin hydroformylation are more active than cobalt carbonyls and can be appHed at lower temperatures and pressures (14). Rhodium hydrocarbonyl [75506-18-2] HRh(CO)4, results in lower -butyraldehyde [123-72-8] to isobutyraldehyde [78-84-2] ratios from propylene [115-07-17, C H, than does cobalt hydrocarbonyl, ie, 50/50 vs 80/20. Ligand-modified rhodium catalysts, HRh(CO)2L2 or HRh(CO)L2, afford /iso-ratios as high as 92/8 the ligand is generally a tertiary phosphine. The rhodium catalyst process was developed joindy by Union Carbide Chemicals, Johnson-Matthey, and Davy Powergas and has been Hcensed to several companies. It is particulady suited to propylene conversion to -butyraldehyde for 2-ethylhexanol production in that by-product isobutyraldehyde is minimized. 

Conventional triorganophosphite ligands, such as triphenylphosphite, form highly active hydroformylation catalysts (95—99) however, they suffer from poor durabiUty because of decomposition. Diorganophosphite-modified rhodium catalysts (94,100,101), have overcome this stabiUty deficiency and provide a low pressure, rhodium catalyzed process for the hydroformylation of low reactivity olefins, thus making lower cost amyl alcohols from butenes readily accessible. The new diorganophosphite-modified rhodium catalysts increase hydroformylation rates by more than 100 times and provide selectivities not available with standard phosphine catalysts. For example, hydroformylation of 2-butene with l,l -biphenyl-2,2 -diyl... 

Propane, 1-propanol, and heavy ends (the last are made by aldol condensation) are minor by-products of the hydroformylation step. A number of transition-metal carbonyls (qv), eg, Co, Fe, Ni, Rh, and Ir, have been used to cataly2e the oxo reaction, but cobalt and rhodium are the only economically practical choices. In the United States, Texas Eastman, Union Carbide, and Hoechst Celanese make 1-propanol by oxo technology (11). Texas Eastman, which had used conventional cobalt oxo technology with an HCo(CO)4 catalyst, switched to a phosphine-modified Rh catalyst ia 1989 (11) (see Oxo process). In Europe, 1-propanol is made by Hoechst AG and BASE AG (12). 

No catalyst has an infinite lifetime. The accepted view of a catalytic cycle is that it proceeds via a series of reactive species, be they transient transition state type structures or relatively more stable intermediates. Reaction of such intermediates with either excess ligand or substrate can give rise to very stable complexes that are kinetically incompetent of sustaining catalysis. The textbook example of this is triphenylphosphine modified rhodium hydroformylation, where a plot of activity versus ligand metal ratio shows the classical volcano plot whereby activity reaches a peak at a certain ratio but then falls off rapidly in the presence of excess phosphine, see Figure... 

They constitute the first rhodium phosphine modified catalysts for such a selective linear hydroformylation of internal alkenes. The extraordinary high activity of 32 even places it among the most active diphosphines known. Since large steric differences in the catalyst complexes of these two ligands are not anticipated, the higher activity of 32 compared to 31 might be ascribed to very subtle bite angle effects or electronic characteristics of the phosphorus heterocycles. 

In 1961 Heck and Breslow presented a multistep reaction pathway to interpret basic observations in the cobalt-catalyzed hydroformylation.28 Later modifications and refinements aimed at including alternative routes and interpreting side reactions.6 Although not all the fine details of hydroformylation are equally well understood, the Heck-Breslow mechanism is still the generally accepted basic mechanism of hydroformylation.6,17,19,29 Whereas differences in mechanisms using different metal catalysts do exist,30 all basic steps are essentially the same in the phosphine-modified cobalt- and rhodium-catalyzed transformations as well. 

The hydroformylation of conjugated dienes with unmodified cobalt catalysts is slow, since the insertion reaction of the diene generates an tj3-cobalt complex by hydride addition at a terminal carbon (equation 10).5 The stable -cobalt complex does not undergo facile CO insertion. Low yields of a mixture of n- and iso-valeraldehyde are obtained. The use of phosphine-modified rhodium catalysts gives a complex mixture of Cs monoaldehydes (58%) and C6 dialdehydes (42%). A mixture of mono- and di-aldehydes are also obtained from 1,3- and 1,4-cyclohexadienes with a modified rhodium catalyst (equation ll).29 The 3-cyclohexenecarbaldehyde, an intermediate in the hydrocarbonylation of both 1,3- and 1,4-cyclo-hexadiene, is converted in 73% yield, to the same mixture of dialdehydes (cis.trans = 35 65) as is produced from either diene. 

Phosphine-modified rhodium catalysts hydroformylate alkynes to saturated aldehydes.1 The reaction most likely proceeds by a rapid hydrogenation to yield the alkene, followed by hydroformylation. 

Nitro groups are tolerated in hydroformylation as are amines, provided they are protected. The reaction of o-nitrostyrene gives an intermediate for the synthesis of 3-methylindole (equation 28).38 With a phosphine-modified rhodium catalyst, the reaction is regioselective, placing the formyl group in the a-posi-tion. 

The hydroformylation mechanism for phosphine-modified rhodium catalysts follows with minor modifications the Heck-Breslow cycle. HRh(CO)(TPP)3 [11] is believed to be the precursor of the active hydroformylation species. First synthesized by Vaska in 1963 [98] and structurally characterized in the same year [99], Wilkinson introduced this phosphine-stabilized rhodium catalyst to hydroformylation five years later [100]. As one of life s ironies, Vaska even compared HRh(CO)(TPP)3 in detail with HCo(CO)4 as an example of structurally related hy-drido complexes [98]. Unfortunately he did not draw the conclusion that the rhodium complex should be used in the oxo reaction. According to Wilkinson, two possible pathways are imaginable the associative and the dissociative mechanisms. Preceding the catalytic cycle are several equilibria which generate the key intermediate HRh(CO)2(TPP)2 (Scheme 4 L = ligand). 

Yildiz-Unveren, H.H. and Schomacker, R. (2005) Hydroformylation with rhodium phosphine-modified catalyst in a microemulsion comparison of organic and aqueous systems for styrene, cyclohexene and l,4-diacetoxy-2-butene. Catal. Lett., 102, 83. 

Thermoregulated phase-transfer catalysis, however, could be successfully put into effect for the hydroformylation of higher olefins in aqueous/organic two-phase media [11], As shown in Table 2, various olefins have been converted to the corresponding aldehydes in the presence of nonionic phosphine-modified rhodium complexes as catalysts. An average turnover frequency (TOF) of 250 h-1 for 1-do-decene and 470 Ir1 for styrene have been achieved. Even the hydroformylation of oleyl alcohol, an extremely hydrophobic internal olefin, would give a yield of 72% aldehyde [19]. In comparison, no reaction occurred if Rh/TPPTS complex was used as the catalyst under the same conditions. 

The concept of TRPTC provides a reasonable explanation for the satisfactory catalytic reactivity of Rh/nonionic phosphine complexes in the case of the two-phase hydroformylation of higher olefins. At a temperature lower than the cloud point, a nonionic phosphine-modified rhodium catalyst would remain in the aqueous phase since the partition of the catalyst between water and a nonpolar aprotic organic solvent strongly favors the aqueous phase. On heating to a temperature higher than the cloud point, however, the catalyst loses its hydrate shell, transfers into the organic phase and then catalyzes the transformation of alkenes to aide-... 

Phosphine modified cobalt catalysts permit the hydroformylation reaction to operate at lower pressure and produce a higher proportion of the normal isomer. Pressure is typically about 35 bars (500 psig) and the nor-mal/iso ratio is between 6 and 7. In the 1970s, Union Carbide in conjunction with Johnson Matthey and Davy McKee developed and improved oxo process based on a rhodium catalyst, modified with a triphenylphosphine (TPP) lipnd. 

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