Hydroformylation rhodium carbonyls

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. 

Most ring syntheses of this type are of modern origin. The cobalt or rhodium carbonyl catalyzed hydrocarboxylation of unsaturated alcohols, amines or amides provides access to tetrahydrofuranones, pyrrolidones or succinimides, although appreciable amounts of the corresponding six-membered heterocycle may also be formed (Scheme 55a) (73JOM(47)28l). Hydrocarboxylation of 4-pentyn-2-ol with nickel carbonyl yields 3-methylenetetrahy-drofuranone (Scheme 55b). Carbonylation of Schiff bases yields 2-arylphthalimidines (Scheme 55c). The hydroformylation of o-nitrostyrene, subsequent reduction of the nitro group and cyclization leads to the formation of skatole (Scheme 55d) (81CC82). 

The less bulky ligand (71) studied by Gladfelter leads to dimeric complexes [Rh2(71)2(CO)2] and even tetramers.222 Transformations of rhodium carbonyl complexes in alkene hydroformylation are discussed from the standpoint of the catalytic system self-control under the action of reaction... 

The first report of rhodium catalysts for aldehyde reduction came from Marko who reported the use of RhCl3 3H20 under hydroformylation conditions [9]. It was suggested that the active species were rhodium carbonyls, and the catalyst system was successfully utilized in the hydrogenation of ethanal, propanal, and benzalde-... 

Pettit and coworkers—metal hydride intermediates by weak base attack over Fe carbonyl catalysts. Pettit et al.ls approached the use of metal carbonyl catalysts for the homogeneous water-gas shift reaction from the standpoint of hydroformyla-tion by the Reppe modification.7 In the typical hydroformylation reaction, an alkene is converted to the next higher aldehyde or alcohol through reaction of CO and H2 with the use of a cobalt or rhodium carbonyl catalyst. However, in the Reppe modification, the reduction is carried out with CO and H20 in lieu of H2 (Scheme 6) ... 

Recently proof has been reported for a heterometallic bimolecular formation of aldehyde from a manganese hydride and acylrhodium species [2], Phosphine free, rhodium carbonyl species show the same kinetics as the cobalt system, i.e. the hydrogenolysis of the acyl-metal bond is rate-determining. Addition of hydridomanganese pentacarbonyl led to an increase of the rate of the hydroformylation reaction. The second termination reaction that takes place according to the kinetics under the reaction conditions (10-60 bar, 25 °C) is reaction (3). The direct reaction with H2 takes place as well, but it is slower on a molar basis than the manganese hydride reaction. 

Facile formation of metal carbonyl complexes makes rhodium a very useful catalyst for both the hydroformylation of multiple bonds and the decarbonylation of the aldehydes. Two groups have independently utilized rhodium carbonyl complex obtained from decarbonylation of aldehydes in PKR (Scheme 5). 

Of the isomeric aldehydes indicated in Eq. (7.1), the linear aldehyde corresponding to anti-Markovnikov addition is always the main product. The isomeric branched aldehyde may arise from an alternative alkene insertion step to produce the [RCH(Me)Co(CO)3] or [RCH(Me)Rh(CO)(PPh3)2] complexes, which are isomeric to 2 and 8, respectively. Alternatively, hydroformylation of isomerized internal alkenes also give branched aldehydes. The ratio of the linear and branched aldehydes, called linearity, may be affected by reaction conditions, and it strongly depends on the catalyst used. Unmodified cobalt and rhodium carbonyls yield about 3-5 1 mixtures of the normal and iso products. 

Under mild conditions, hydroformylation of olefins with rhodium carbonyl complexes selectively produces aldehydes. A one-step synthesis of oxo alcohols is possible using monomeric or polymeric amines, such as dimethylbenzylamine or anion exchange resin analog to hydrogenate the aldehyde. The rate of aldehyde hydrogenation passes through a maximum as amine basicity and concentration increase. IR data of the reaction reveal that anionic rhodium carbonyl clusters, normally absent, are formed on addition of amine. Aldehyde hydrogenation is attributed to enhanced hydridic character of a Rh-H intermediate via amine coordination to rhodium. 

Data are presented to identify some of the important factors in aldehyde hydrogenation and to characterize rhodium carbonyl chemistry under hydroformylation conditions. Comparison is made of the effects of monomeric and of polymeric amines, and a possible reaction mechanism is examined in the light of the data. 

Amine profoundly alters the predominant rhodium carbonyl species in hydroformylation mixtures as shown in Table VI. At the higher... 

In the hydroformylation of olefins over rhodium carbonyl catalysts, aldehyde hydrogenation was noted under mild conditions in the absence of amine. Rates of hydrogenation passed through a maximum with increasing amine basicity and concentration. 

For cis-chelate complexes of rhodium and bisphosphines as catalysts, indeed relatively low ratios of n/i aldehyde products were reported (12, 13). Using a 1 1 mixture of H CO at atmospheric pressure, Sanger reported n/i ratios ranging from 3 to 4 for propylene hydroformylation (12). However, his catalyst systems were produced by adding less than 2 mol of bisphosphine per mole tris(triphenyl-phosphine)rhodium carbonyl hydride. When an excess of the chelating bisphosphines was used by Pittman and Hirao (13), low n/i ratios close to 1 were produced from 1-pentene using a mixture of H2/CO at 100-800 psi between 60° and 120°C. 

Since the 1-olefin concentration-dependent hydroformylation in the presence of the above catalyst system has a slightly higher activation energy of about 22 kcal mol-1, it is proposed that the ratedetermining step of selective terminal 1-olefin hydroformylation may involve a transition state leading to the formation of a 1-alkyl bis-(trans-phosphine)rhodium carbonyl hydride complex rather than the dissociation of the trisphosphine complex. 

Fell, B., Schobben, C. and Papadogianakis, G. (1995) Hydroformylation of homologous C0-alkenecarboxylate esters with water soluble rhodium carbonyl/tertiary phosphine complex catalyst systems. J. Mol. Catal. A Chem., 101, 179. 

Fell also described the hydroformylation of fatty acids with heterogenized cobalt carbonyl and rhodium carbonyl catalysts [37]. The products of the reaction with polyunsaturated fatty acids were, depending on the catalyst metal, poly- or monoformyl products. The catalyst carrier was a silicate matrix with tertiary phosphine ligands and cobalt or rhodium carbonyl precursors on the surface. The cobalt catalyst was applied at 160-180°C and gave mostly monofunctionalized fatty acid chains. With linoleic acid mixtures, the corresponding rhodium catalyst gave mono- and diformyl derivatives. Therefore, the rhodium catalyst was more feasible for polyfunctionalized oleocompounds. The reaction was completed in a batch experiment over 10 h at 100 bar and 140°C rhodium leaching was lower than 1 ppm. 

Fell B, Leckel D, Schobben C (1995) Micellar two phase-hydroformylation of multiple unsaturated fatty substances with water soluble rhodium carbonyl/tertiary phosphane complex catalyst systems. Fett Wiss Technol 97 219-228... 

Xia Z, Kloeckner U, Fell B (1996) Hydroformylation of mono and multiple unsaturated fatty substances with heterogenized cobalt carbonyl and rhodium carbonyl catalysts. Fett/Lipid 98 313-321... 

A RhNaY (1 wt.% Rh) catalyst was prepared by ion exchange using an aqueous solution of [Rh(NH3)6]Cl3 (226, 229), followed by treatment with a CO/H2 (1/1) mixture at 130°C and 80 atm pressure. The catalyst so formed was observed to have good activity and high total aldehyde selectivity ( 95%) for the liquid-phase hydroformylation of hexene-1. Some typical results are shown in Table VI, which indicate that the normal/iso aldehyde product ratio is similar to that obtained with homogeneous rhodium carbonyl catalysts (223). 

The authors also claimed that the zeolite catalyst exhibited unusually high selectivity to dialdehydes (60%) in the hydroformylation of 1,5-hexadiene. Unfortunately, comparative data obtained under similar conditions with homogeneous rhodium carbonyl catalysts were not presented. 

For hydroformylation over cobalt and rhodium zeolites the active species have not been defined. However, in the case of RhNaY the in situ formation of a rhodium carbonyl cluster has been identified (226) by infrared spectroscopy. Interestingly, this cluster appears to be different from known compounds such as Rh4(CO)12 and Rh6(CO)16. This does suggest that alternative carbonyl clusters may possibly be formed in zeolites due to the spatial restrictions of the intracrystalline cavities. The mechanism of hydroformylation in these zeolites is probably similar to that known for homogeneous catalysis. 

The scheme reduces to its most simple form when carbon monoxide is the only ligand present in the system, because equilibria of mixed ligand/carbon monoxide complexes do not occur. The kinetics of the hydroformylation reaction using hydrido rhodium carbonyl as the catalyst was studied by Marko [20]. For 1-pen-tene the rate expression found is ... 

The hydroformylation of 1-hexene catalyzed by rhodium carbonyl has recently been studied by Lazzaroni and coworkers [21]. They were particularly interested in the influence of reaction parameters on the regioselectivity and the chemoselectivity (to aldehyde and 2-hexene). To understand their results we have to extend Scheme 6.1 by taking account of the formation of linear and branched aldehydes, as well as of isomerization. This is shown in Scheme 6.2. 

Another similarity between HCo(CO)4 and HRh(CO)4 is that they are only stable under certain reaction conditions. Unlike HCo(CO)4, HRh(CO)4 does not usually precipitate out as metallic rhodium, but rather forms stable rhodium carbonyl clusters such as Rli4(CO)i2 and Rh6(CO)i6- Indeed, just as Co2(CO)g is a common catalyst precursor for cobalt hydroformylation, Rh4(CO)i2 is often used as a starting species for rhodium hydroformylation. 

A plausible mechanism was reported for the catalytic formation of benzene resulting from phosphorus-carbon bond cleavage which occurs during propylene hydroformylation catalyzed by triphenylphos-phine-substituted rhodium carbonyls under higher H2 partial pressures (Scheme 37). " ... 

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