Rhodium Hydroformylation Research Articles

Regioselective hydroformylation of propene catalysed by rhodium-zeolite.

Hydroformylation is an industrial process for the production of aldehydes from alkenes1,2. Regioselective hydroformylation of propene to high-value n-butanal is particularly important, owing to a wide range of bulk applications of n-butanal in the manufacture of various necessities in human daily life3. Supported rhodium (Rh) hydroformylation catalysts, which often excel in catalyst recyclability, ease of separation and adaptability for continuous-flow processes, have been greatly exploited4. Nonetheless, they usually consist of rotationally flexible and sterically unconstrained Rh hydride dicarbonyl centres, only affording limited regioselectivity to n-butanal5-8. Here we show that proper encapsulation of Rh species comprising Rh(I)-gem-dicarbonyl centres within a MEL zeolite framework allows the breaking of the above model. The optimized catalyst exhibits more than99% regioselectivity to n-butanal and more than99% selectivity to aldehydes at a product formation turnover frequency (TOF) of 6,500 h-1, surpassing the performance of all heterogeneous and most homogeneous catalysts developed so far. Our comprehensive studies show that the zeolite framework can act as a scaffold to steer the reaction pathway of the intermediates confined in the space between the zeolite framework and Rh centres towards the exclusive formation of n-butanal.

Heterogeneous Phosphine-Containing Hydroformylation Catalysts Based on Modified Porous Organic Framework

A series of heterogeneous phosphine-containing rhodium hydroformylation catalysts based on porous aromatic frameworks (PAFs) were prepared. The catalysts PAF30-MDEA-TPPTS-Rh (TPPTS is trisodium triphenylphosphine-3,3',3''-trisulfonate, MDEA is methyldiethanolamine fragment) and PAF-30-Im-TPPTS-Rh (Im is imidazole fragment) showed the highest stability in repeated use in 1-hexene hydroformylation. The catalyst PAF-30-MDEA-TPPTS-Rh before and after use in hydroformylation was characterized by elemental C,N,H,S analysis, inductively coupled plasma atomic absorption spectroscopy, low-temperature nitrogen adsorption–desorption, transmission electron microscopy, IR spectroscopy, and X-ray photoelectron spectroscopy. The effect of temperature, pressure, and solvent on the course of hydroformylation in the presence of PAF-30-MDEA-TPPTS-Rh was studied. The catalyst is active in hydroformylation of a series of unsaturated compounds, including functionalized substrates and olefins with internal double bond.

Effect of Ligand Backbone on the Selectivity and Stability of Rhodium Hydroformylation Catalysts Derived from Phospholane-Phosphites

A study on how ligand backbone structure has an impact on selectivity, rate, and catalyst stability of hydroformylation catalysts was prompted by some longer-term stability issues being discovered ...

Dynamic Release–Immobilization of a Homogeneous Rhodium Hydroformylation Catalyst by a Polyoxometalate Metal–Organic Framework Composite

AbstractThermal treatment of phosphotungstic acid (PTA)‐MIL‐101(Cr) composites in the presence of hydroformylation catalyst RhH(CO)(PPh3)3 leads to immobilization of the homogeneous Rh complex within the metal–organic framework (MOF) scaffold by coordination of PTA‐Rh. The Rh complex‐containing MOFs are tested in the hydroformylation of 1‐octene in which PTA competes with CO during ligand association. In the presence of the carbonyl ligand, the Rh complex is released from the MOF and behaves as a homogeneous catalyst. Therefore, the product spectra and selectivities of the Rh complex‐containing MOFs are similar to those of RhH(CO)(PPh3)3. Upon CO evacuation, Rh recoordinates to PTA, allowing for easy recycling of this new pseudo‐heterogeneous catalyst.

Capsule-controlled selectivity of a rhodium hydroformylation catalyst

Chemical processes proceed much faster and more selectively in the presence of appropriate catalysts, and as such the field of catalysis is of key importance for the chemical industry, especially in light of sustainable chemistry. Enzymes, the natural catalysts, are generally orders of magnitude more selective than synthetic catalysts and a major difference is that they take advantage of well-defined cavities around the active site to steer the selectivity of a reaction via the second coordination sphere. Here we demonstrate that such a strategy also applies for a rhodium catalyst; when used in the hydroformylation of internal alkenes, the selectivity of the product formed is steered solely by changing the cavity surrounding the metal complex. Detailed studies reveal that the origin of the capsule-controlled selectivity is the capsule reorganization energy, that is, the high energy required to accommodate the hydride migration transition state, which leads to the minor product.

Chemo‐ and Regioselective Homogeneous Rhodium‐Catalyzed Hydroamidomethylation of Terminal Alkenes to N‐Alkylamides

A rhodium/xantphos homogeneous catalyst system has been developed for direct chemo- and regioselective mono-N-alkylation of primary amides with 1-alkenes and syngas through catalytic hydroamidomethylation with 1-pentene and acetamide as model substrates. For appropriate catalyst performance, it appears to be essential that catalytic amounts of a strong acid promoter, such as p-toluenesulfonic acid (HOTs), as well as larger amounts of a weakly acidic protic promoter, particularly hexafluoroisopropyl alcohol (HOR(F) ) are applied. Apart from the product N-1-hexylacetamide, the isomeric unsaturated intermediates, hexanol and higher mass byproducts, as well as the corresponding isomeric branched products, can be formed. Under optimized conditions, almost full alkene conversion can be achieved with more than 80% selectivity to the product N-1-hexylamide. Interestingly, in the presence of a relatively high concentration of HOR(F) , the same catalyst system shows a remarkably high selectivity for the formation of hexanol from 1-pentene with syngas, thus presenting a unique example of a selective rhodium-catalyzed hydroformylation-hydrogenation tandem reaction under mild conditions. Time-dependent product formation during hydroamidomethylation batch experiments provides evidence for aldehyde and unsaturated intermediates; this clearly indicates the three-step hydroformylation/condensation/hydrogenation reaction sequence that takes place in hydroamidomethylation. One likely role of the weakly acidic protic promoter, HOR(F) , in combination with the strong acid HOTs, is to establish a dual-functionality rhodium catalyst system comprised of a neutral rhodium(I) hydroformylation catalyst species and a cationic rhodium(III) complex capable of selectively reducing the imide and/or ene-amide intermediates that are in a dynamic, acid-catalyzed condensation equilibrium with the aldehyde and amide in a syngas environment.

Bis-(thiosemicarbazonato) Zn(ii) complexes as building blocks for construction of supramolecular catalysts

In this paper we report the application of bis-(thiosemicarbazonato) Zn(II) complexes as building blocks in the construction of supramolecular transition metal assemblies. We investigated their coordination behaviour towards pyridylphosphine molecules and found these systems comparable to those based on Zn(porphyrin) and Zn(salphen) complexes. Additionally, catalytic experiments and an in situ high-pressure FTIR study of the supramolecular rhodium hydroformylation catalysts, assembled using the bis-(thiosemicarbazonato) Zn(II) complexes, demonstrate their applicability in supramolecular catalysis and their potential for application in other areas of supramolecular chemistry.

Bite angle effects of diphosphines in C–C and C–X bond forming cross coupling reactions

Catalytic reactions of C-C and C-X bond formation are discussed in this critical review with particular emphasis on cross coupling reactions catalyzed by palladium and wide bite angle bidentate diphosphine ligands. Especially those studies have been collected that allow comparison of the ligand bite angles for the selected ligands: dppp, BINAP, dppf, DPEphos and Xantphos. Similarities with hydrocyanation and CO/ethene/MeOH reactions have been highlighted, while rhodium hydroformylation has been mentioned as a contrasting example, in which predictability is high and steric and electronic effects follow smooth trends. In palladium catalysis wide bite angles and bulkiness of the ligands facilitate generally the reductive elimination thus giving more efficient cross coupling catalysis (174 references).

Phenylphosphatrioxa-adamantanes: bulky, robust, electron-poor ligands that give very efficient rhodium(i) hydroformylation catalysts

The cage phosphines 1,3,5,7-tetramethyl-6-phenyl-2,4,8-trioxa-6-phosphaadamantane (1a) and 1,3,5,7-tetraethyl-6-phenyl-2,4,8,trioxa-6-phosphaadamantane (1b) have been made by the acid catalysed addition of PhPH(2) to the appropriate beta-diketones; the acid used (HCl, H(3)PO(4) or H(2)SO(4)) and its concentration affect the rate and selectivity of these condensation reactions. Phosphines 1a and 1b react with [PdCl(2)(NCPh)(2)] to form complexes trans-[PdCl(2)(1a)(2)](2a) and trans-[PdCl(2)(1b)(2)](2b) as mixtures of rac and meso diastereoisomers. The platinum(II) chemistry is more complicated and when 1a or 1b is added to [PtCl(2)(cod)], equilibrium mixtures of trans-[PtCl(2)L(2)] and [Pt(2)Cl(4)L(2)](L = or ) are formed in CH(2)Cl(2) solution. Meso/rac mixtures of trans-[MCl(CO)(1a)(2)] M = Ir (6a) or Rh (7a) are formed upon treatment of MCl(3).nH(2)O with an excess of 1a and the anionic cobalt complex [NHEt(3)][CoCl(3)(1a)](9) was isolated from the product formed by CoCl(2).6H(2)O and 1a. The nu(CO) values from the IR spectra of 6a and 7a suggest that 1a resembles a phosphonite in its bonding to Rh and Ir. Crystal structures of meso-2a, meso-2b, rac-6a and 9 are reported and in each case a small intracage C-P-C angle of ca. 94 degrees is observed; this may partly explain the bonding characteristics of ligands 1a and 1b. The cone angles for 1a and 1b are similar and large (ca. 200 degrees). Rhodium complexes of ligands 1a and 1b are hydroformylation catalysts with similarly high activity to catalysts derived from phosphites. The catalysts derived from 1a and 1b gave unusually low linear selectivity in the hydroformylation of hexenes. This feature has been further exploited in quaternary-selective hydroformylations of unsaturated esters; catalysts derived from 1a give better yields and regioselectivities than any previously reported catalyst.

Rhodium Complexes of Sterically Demanding Diphosphonites: Coordination Chemistry and Catalysis

The coordination chemistry of various sterically constrained diphosphonites 1−6 with rhodium are reported. The stoichiometric reaction of ligand 5 with [Rh(μ-Cl(CO)2]2 gives rise to the sole formation of trans-[RhCl(CO)(5)] (7), as shown by NMR and IR spectroscopy and X-ray crystallography. The molecular structure reveals a weak interaction between the metal center and the oxygen from the xanthene backbone. This complex serves as a structural model for the first intermediate in the catalytic cycle of rhodium hydroformylation, [Rh(H)(CO)(P⌒P)]. A detailed study on the solution structure of the catalyst resting state under catalytic conditions is performed by high-pressure NMR and FT-IR spectroscopy. The spectroscopic data show that under hydroformylation conditions the bidentate ligands form well-defined complexes with the structure [Rh(H)(CO)2(P⌒P)]. All ligands show preference for a bis-equatorial (ee) coordination mode in the trigonal-bipyramidal Rh complexes. These novel sterically constrained diphosph...

Dormant states of rhodium hydroformylation catalysts: carboalkoxyrhodium complex formed from enones in the alkene feed.

Catalysts get food poisoning: Conversion of the active 1-alkene hydroformylation catalyst 1 with reactive impurities in the feed, such as dienes and enones, into unreactive rhodium intermediates leads to deactivation of 1. For example, 2 is much more reactive towards 1 than the substrate and transforms it temporarily into 4 blocking the hydroformylation activity.

Dormant States of Rhodium Hydroformylation Catalysts: Carboalkoxyrhodium Complex Formed from Enones in the Alkene Feed

Gift für den Katalysator: Die Reaktion von 1, einem Hydroformylierungskatalysator für 1-Alkene, mit Verunreinigungen wie Dienen und Enonen im Substrat führt zur Desaktivierung: Enon 2 reagiert bevorzugt mit 1 unter Bildung des unreaktiven Rhodium-Komplexes 4. Die Hydroformylierungsaktivität wird dadurch zeitweise gehemmt.

Wide bite angle amine, arsine and phosphine ligands in rhodium- and platinum/tin-catalysed hydroformylation †

New wide bite angle amine, arsine and mixed phosphineamine and phosphinearsine ligands based on xanthene backbones were synthesized. The co-ordination chemistry and the catalytic performance of these ligands were compared to those of the parent phosphine ligands. The amine based xanthene ligands do not form rhodium–hydride complexes and therefore give very poor rhodium hydroformylation catalysts. The catalytic performance of the xantarsine and the mixed xantphosarsine ligands is comparable with that of the xantphos ligands and they form similar (ligand)Rh(CO)2H and [(ligand)Rh(CO)2]2 complexes. In the platinum/tin-catalysed hydroformylation the xantarsine and the mixed xantphosarsine ligands proved to be superior to the xantphos ligands. The remarkably high selectivity and activity that is displayed by the mixed xantphosarsine ligand is explained by its wide natural bite angle and the formation of cis co-ordinated platinum complexes.

Polymer‐bound bulky‐phosphite modified rhodium hydroformylation catalysts

AbstractAttachment of phosphites to styrene copolymers is described which are used as rhodium hydroformylation catalysts. The influence of the chain loading on the activity and complex formation of three types of copolymer‐bound rhodium hydroformylation catalysts in comparison with their low molecular weight analogues has been studied. The catalytic activity of the polystyrene‐bound system with the most bulky phosphite, the first system studied, is identical to that of the low molecular weight analogue. The catalysts show a high activity towards the hydroformylation of the otherwise unreactive cyclooctene. It was found that only one phosphite is coordinated to the rhodium complex in its active form. An equilibrium between this complex and an inactive complex without phosphite ligands prohibits its use in continuous flow reactors.Secondly, as polymer support a perfectly random copolymer of styrene and less bulky 3,3′,5,5′‐tetra‐tert‐butylbiphenyl‐2,2′‐diyl p‐vinylphenylphosphite was used. The chain loading α of this copolymer with phosphite ligands has a large influence on the complex formation of the catalyst. With high chain loadings moderately active bis‐phosphite catalysts are formed. Low chain loadings give active, easily accessible, monophosphite complexes. The active species in the hydroformylation of sterically hindered alkenes is a mono‐phosphite rhodium complex. The activity of the copolymer‐bound catalyst towards the hydroformylation of cyclooctene is found to be as high as the activity of its low molecular weight analogue. For styrene, this polymer catalyst yields a slower catalyst than the low‐molecular weight analogue.The third part demonstrates that silica‐grafted polymer‐bound phosphite modified rhodium complexes can be used in continuous flow reactors. The hydroformylation of styrene was carried out at moderate pressure (pCO/H2 = 3 MPa) and temperature (T = 100°C), yielding constant conversions over a period of at least ten days. These positive results were obtained in benzene as a solvent and for a ligand to rhodium ratio of only four.

Aqueous phase rhodium hydroformylation of octene-1 with trisulfonated tris (ω-phenyl)alkylphosphines and trisulfonated triphenyl phosphine. Reaction selectivity as an indication of rhodium-phosphine complex chemistry

The electron donating, water soluble phosphines, P[ (CH 2) x C 6H 4- p-SO 33Na] 3, x=1, 2, 3, 6, are used to generate aqueous rhodium catalysts for the hydroformylation of octene-1. At low L/ Rh ratios conversion generally increases with increasing number of methylene groups. At high L/ Rh ratios the catalytic activity decreases. For comparison data are given for P (C 6H 4- m-SO 3Na) 3, TPPTS, as well. The new complexes, Rh (acac) (CO)L, where L=P[ (CH 2) x C 6H 4- p-SO 3Na] 3, x=1, 2, 3, 6, and HRh (CO)L 3 where L=P[(CH 2) 2 C 6H 4- p-SO 3Na] 3, are described. The latter compound, HRh (CO)L 3, appears to oxidatively add water to yield [H 2Rh(CO)L 3] +.

Stable silica-grafted polymer-bound bulky-phosphite modified rhodium hydroformylation catalysts

The present study demonstrates that silica-grafted polymer-bound phosphite modified rhodium complexes can be used in continuous flow reactors. The hydroformylation of styrene was carried out at moderate pressure ( p(CO/H 2)=30 bar) and temperature ( T=1OO°C), yielding constant conversions over a period of at least ten days. Leakage of rhodium is prevented totally and no decay in catalyst activity was observed. These positive results were obtained in benzene as a solvent and for a ligand to rhodium ratio of only 4. When toluene was used as solvent, considerable rhodium leaching was observed. This could be attributed to contraction of the grafted polymer coils in this solvent, leading to incomplete coordination of rhodium.

Fine tuning of bulky-phosphite modified rhodium catalysts by binding them to copolymers

The influence of the chain loading on the activity and complex formation of a copolymer-bound rhodium hydroformylation catalyst in comparison with its low molecular weight analogue has been studied in detail. As polymer support a perfectly random copolymer of styrene and 2,2′-bis(4,6-di- t-butylphenyl)- p-styryl phosphite ( 2) was used. The chain loading, α, of this copolymer with phosphite ligands has a large influence on the complex formation of the catalyst. With high chain loadings moderately active bis-phosphite catalysts are formed. Low chain loadings give active, easily accessible, mono-phosphite complexes. Study of the copolymer-bound catalysts yielded mechanistic information about the catalytic species involved in the hydroformylation of styrene and cyclooctene. The active species in the hydroformylation of sterically hindered alkenes is a mono-phosphite rhodium complex. The activity of the catalyst can be enhanced if excess phosphite is used. This effect was ascribed to faster reaction with hydrogen of bis-phosphite rhodium intermediate (s). The activity of the copolymer-bound catalyst towards the hydroformylation of cyclooctene is found to be as high as the activity of its low molecular weight analogue. The hydroformylation of styrene proceeds more slowly.

A new type of highly active polymer-bound rhodium hydroformylation catalyst

A new route of attaching phosphites to a (co)polymer chain is described. These copolymers are used for the preparation of a rhodium phosphite hydroformylation catalyst. The catalytic activity of this polymer-bound system is identical to that of the low molecular weight analogue. The catalysts show a high activity towards the hydroformylation of the otherwise unreactive cyclooctene. From spectroscopic and kinetic data, it was found that only one phosphite is coordinated to the rhodium complex in its active form. An equilibrium between this complex and an inactive complex without phosphite ligands, prohibits its use in continuous flow reactors.

ChemInform Abstract: Supported Aqueous‐Phase, Rhodium Hydroformylation Catalysts. Part 2. Hydroformylation of Linear, Terminal and Internal Olefins.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Supported aqueous-phase, rhodium hydroformylation catalysts I. New methods of preparation

Improved methods for the preparation of supported aqueous phase (SAP) catalysts are described. An in situ preparation of the supported rhodium complex and a more effective hydration procedure are presented. SAP catalysts are also prepared by a self-assembly experiment in which the separated components of a SAP catalyst spontaneously adopt a SAP configuration under reaction conditions.