Selectivity of Rhodium‐Catalyzed Hydroformylation of 1‐Octene during Batch and Semi‐Batch Reaction using Trifluoromethyl‐Substituted Ligands

The regioselectivity of catalysts generated in situ from dicarbonyl rhodium(I)(2,4‐pentanedione) and trifluoromethyl‐substituted triphenylphosphine ligands has been evaluated during the hydroformylation of 1‐octene. The influence of batch or semi‐batch operation, the solvent, and the number of trifluoromethyl substituents has been investigated. During batch operation in a supercritical carbon dioxide (CO₂)‐rich system the differential n:iso ratio increases from approximately 4 to a value of 12–16 at about 90–95 % conversion for the catalyst based on bis[3,5‐bis(trifluoromethyl)phenyl]phenylphosphine. For semi‐batch conditions using hexane a constant n:iso ratio is obtained over a broad conversion range. Batch hydroformylation in neat 1‐octene is faster than in a supercritical CO₂‐rich, one‐phase system, with a similar overall selectivity as observed in the supercritical case. The results provide further directions for the development of ligands that are especially designed for the separation of homogeneous catalysts in continuously operated hydroformylation in scCO₂.     

Heptakis(2,3‐di‐O‐methyl‐6‐O‐sulfopropyl)‐β‐cyclodextrin: A Genuine Supramolecular Carrier for Aqueous Organometallic Catalysis

The behavior of heptakis(2,3‐di‐O‐methyl‐6‐O‐sulfopropyl)‐β‐cyclodextrin as inverse phase transfer catalyst in biphasic Tsuji–Trost and hydroformylation reactions has been investigated. In terms of activity, this methylated sulfopropyl ether β‐cyclodextrin is much more efficient than the randomly methylated β‐cyclodextrin, which was the most active cyclodextrin known to date. From a selectivity point of view, the intrinsic properties of the catalytic system are fully preserved in the presence of this cyclodextrin as the chemo‐ or regioselectivity was found to be identical to that observed without a mass transfer promoter in the hydroformylation reaction. The efficiency of this cyclodextrin was attributed to its high surface activity and to the absence of interactions with the catalytically active species and the water‐soluble phosphane used to dissolve the organometallic catalyst in the aqueous phase.     

n‐butane carbonylation to n‐pentanal using a cascade reaction of dehydrogenation and SILP‐catalyzed hydroformylation

A novel gas‐phase process has been developed that allows direct two‐step conversion of butane into pentanals with high activity and selectivity. The process consists of alkane dehydrogenation over a heterogeneous Cr/Al₂O₃ catalyst followed by direct gas‐phase hydroformylation using advanced supported ionic liquid phase (SILP) catalysis. The latter step uses rhodium complexes modified with the diphosphite ligands biphephos (BP) and benzopinacol to convert the butane/butene mixture from the dehydrogenation step efficiently into aldehydes. The use of the BP ligand results in improved yields of linear pentanal because SILP systems with this ligand are active for both isomerization and hydroformylation. © 2014 American Institute of Chemical Engineers AIChE J, 61: 893–897, 2015     

Phenoxaphosphino‐Modified Xantphos‐Type Ligands in the Rhodium‐Catalysed Hydroformylation of Internal and Terminal Alkenes

The solubility of the modifying ligand is an important parameter for the efficiency of a rhodium‐catalysed hydroformylation system. A facile synthetic procedure for the preparation of well‐defined xanthene‐type ligands was developed in order to study the influence of alkyl substituents at the 2‐, and 7‐positions of the 9,9‐dimethylxanthene backbone and at the 2‐, and 8‐positions of the phenoxaphosphino moiety of ligands 1 – 16 on solubility in toluene and the influence of these substituents on the performance of the ligands in the rhodium‐catalysed hydroformylation. An increase in solubility from 2.3 mmol⋅L⁻¹ to >495 mmol⋅L⁻¹ was observed from the least soluble to the most soluble ligand. A solubility of at least 58 mmol⋅L⁻¹ was estimated to be sufficient for a large‐scale application of these ligands in hydroformylation. Highly active and selective catalysts for the rhodium‐catalysed hydroformylation of 1‐octene and trans‐2‐octene to nonanal, and for the hydroformylation of 2‐pentene to hexanal were obtained by employing these ligands. Average rates of >1600 (mol aldehyde) × (mol Rh)⁻¹×h⁻¹ {conditions: p(CO/H₂) = 20 bar, T = 353 K, [Rh] = 1 mM, [alkene] = 637 mM} and excellent regio‐selectivities of up to 99% toward the linear product were obtained when 1‐octene was used as substrate. For internal olefins average rates of >145 (mol aldehyde)×(mol Rh)⁻¹×h⁻¹ {p(CO/H₂) = 3.6–10 bar, T = 393 K, [Rh] = 1 mM, [alkene] = 640–928 mM} and high regio‐selectivities up to 91% toward the linear product were obtained.     

Improving Aqueous Biphasic Hydroformylation of Unsaturated Oleochemicals Using a Jet‐Loop‐Reactor

In two case studies, the reaction performance of the aqueous biphasic hydroformylation of two industrially relevant oleochemicals, namely methyl 10‐undecenoate (case 1) and methyl oleate (case 2), is significantly improved by the use of a Jet‐Loop Reactor concept. Based on previously reported studies, only the two green and benign co‐solvents, 1‐butanol and isopropanol are applied, respectively, in the absence of any additional auxiliary. Both reactions benefit highly from using this special piece of equipment, specifically designed for improving gas–liquid–liquid mixing to create large interfacial areas with no moving internals. In case 1, the loading of the co‐solvent 1‐butanol is successfully reduced. For the first time significant yields (>40% after 1 h) are obtained in the absence of any co‐solvent, which is very beneficial, since aldehyde products and substrate form a pure product phase enabling straightforward separation. In case 2, the loading of the substrate methyl oleate is successfully increased from 6 to 30 wt% still showing satisfying productivity. At 15 wt%, the yield of the desired internal aldehydes in the jet‐loop reactor is increased by a factor of five compared to a stirred tank reactor after 3 h. Practical Applications: The production of aldehydes from hydroformylation of olefins is highly relevant for the chemical industry, since these can undergo numerous subsequent reactions, to form for instance alcohols, amines, and carboxylic acids. Generally, aldehydes from oleochemicals can serve as platform chemicals for gaining access to bifunctional molecules, which are interesting as polymer precursors. Performing hydroformylation with a water‐based solvent system enables efficient product separation from the aqueous catalyst phase for the realzation of more sustainable processes. By using the Jet‐Loop Reactor, the performance of the reaction system can be greatly improved addressing its practical relevance.     

Synthetic Applications of Synergism using Catalytic Binuclear Elimination Reactions. Further Examples of Rhodium‐Manganese and Rhodium‐Rhenium‐Catalyzed Hydroformylations

Synergism has been previously observed in both rhodium‐manganese‐ and rhodium‐rhenium‐catalyzed hydroformylation. Furthermore, detailed in situ spectroscopic investigations have conclusively shown that the phenomenological origin of this synergistic effect is catalytic binuclear elimination (J. Am. Chem. Soc. 2003 , 125, 5540–5548; 2007 , 129, 13327–13334). In the present contribution, further substrates are used in the hydroformylation reaction with both rhodium‐manganese and rhodium‐rhenium. In situ spectroscopic studies show that (i) significant rate enhancements occur in the mixed metal systems with the new substrates and (ii) the organometallics present in the active systems, and their concentration profiles are consistent with those present in the previously studied catalytic binuclear elimination reactions (CBER). It is therefore concluded that catalytic binuclear elimination is a rather general mechanism in mixed metal hydroformylations and is rather independent of the substrates used. Further discussion is given to mechanistic aspects, synthetic efficiency, and the possibility that such synergistic effects might be useful to other classes of organic syntheses.     

Rhodium‐Catalyzed Highly Regioselective Hydroformylation‐Hydrogenation of 1,2‐Allenyl‐Phosphine Oxides and ‐Phosphonates

The rhodium‐catalyzed hydroformylation‐hydrogenation of 1,2‐allenyl‐phosphine oxides and ‐phosphonates is reported in this paper. The regioselectivity was well controlled, affording only saturated linear γ‐phosphinyl aldehydes under the standard conditions: (carbonyl)tris(triphenylphosphine)‐rhodium hydride [RhH(CO)(PPh₃)₃] (3 mol%), triphenylphosphine (PPh₃) (10 mol%), carbon monoxide (CO) (2.4×10⁶ Pa), hydrogen (H₂) (subsequently charged to 4.8×10⁶ Pa), toluene, 100 °C, 24 h.     

Synthesis of Alcohols via a Rhodium‐Catalyzed Hydroformylation– Reduction Sequence using Tertiary Bidentate Amine Ligands

The synthesis of alcohols from aromatic olefins is described using a rhodium‐catalyzed hydroformylation–reduction sequence with the assistance of a tertiary diamine ligand. The alcohols are produced in excellent branched to linear ratios and in good to excellent isolated yields. In all cases no aldehyde product, from hydroformylation, or alkyl product, from olefin reduction, was detected.     

Tandem Hydroformylation/Acyloin Reaction – The Synergy of Metal Catalysis and Organocatalysis Yielding Acyloins Directly from Olefins

A novel, atom efficient, orthogonal tandem catalysis was developed yielding acyloin products (α‐hydroxy ketones) directly from olefins under hydroformylation conditions. The combination of a metal‐catalysed hydroformylation and an organocatalysed acyloin reaction provides three atom efficient C C bond formations to linear, multifunctional molecules via linkage of the intermediate n‐aldehydes. Additionally, the rhodium catalyst system gives a high n/bra ratio with an exclusive conversion of the terminal double bond in the hydroformylation and the n‐aldehydes are converted selectively to their acyloins.

     

Rhodium Complexed C2‐PAMAM Dendrimers Supported on Large Pore Davisil Silica as Catalysts for the Hydroformylation of Olefins

Polyamidoamine (PAMAM) dendrimers up to the third generation were grown for the first time on the surface of a large‐pore (18 nm) Davisil silica support. The supported dendrimers of generations 0, 1, 2 and 3 were phosphinomethylated and complexed with rhodium. All the generations were found to be very active for the hydroformylation of olefins. The hydroformylation of 1‐octene was accomplished with a turnover frequency of 1700 h⁻¹ at 70 °C. The G(1) material was found to be the most active when the different generations were compared at 50% conversion at 70 °C     

One‐Pot Carbon Monoxide‐Free Hydroformylation of Internal Olefins to Terminal Aldehydes

A one‐step hydroformylation of mixtures of internal and terminal olefins yielding terminal aldehydes without the need for carbon monoxide has been developed. Treatment of the olefin mixtures with Rh catalysts and pinacolborane leads to isomerization and hydroboration in one step. Homologation and subsequent oxidation regiospecifically afford the terminal aldehyde. Good overall yields are obtained for all substrates examined.     

Isomerizing hydroformylation of fatty acid esters: Formation of ω‐aldehydes

The isomerizing hydroformylation of fatty acid esters to oleochemicals with an additional ω‐standing aldehyde group can be performed at a relatively low temperature of 115 °C and a synthesis gas pressure of 20 bar. In the case of oleic acid ester, the best yield of linear aldehyde is 26%; in the case of linoleic acid ester, it is 34%. For both fatty compounds, a strong hydrogenation side reaction is observed, which can be explained by a steering effect of the ester group. The ester function of the fatty compounds makes hydroformylation in the surrounding area of this group impossible. Reactions with the model substances ethyl crotonate and ethyl sorbate showed that hydrogenation predominates, leading to the corresponding saturated compounds.     

Stereoselective Synthesis of β‐Proline Derivatives from Allylamines via Domino Hydroformylation/Wittig Olefination and Aza‐Michael Addition

Under appropriate reaction conditions, a domino hydroformylation/Wittig olefination can be accomplished with derivatives of allylamines and stabilized Wittig ylides. A further highly diastereoselective aza‐Michael reaction yields β‐proline derivatives. These are, for example, useful as building blocks for alkaloid syntheses.     

High‐Pressure 31P{1H} NMR Studies of RhH(CO)(TPPTS)3 in the Presence of Methylated Cyclodextrins: New Light on Rhodium‐Catalyzed Hydroformylation Reaction Assisted by Cyclodextrins

The effect of methylated cyclodextrins on the RhH(CO)(TPPTS)₃ complex in hydroformylation conditions [50 atm of CO/H₂ (1/1) and 80 °C] has been investigated by high‐pressure ³¹P{¹H} NMR spectroscopy. In the presence of methylated β‐cyclodextrin, the equilibria between the rhodium species lie in favor of phosphine low‐coordinated rhodium species. The formation of a stable inclusion complex between this cyclodextrin and the trisulfonated triphenylphosphine ligand (TPPTS) was found to be the key to understanding the displacement of the equilibria. Indeed, the methylated α‐cyclodextrin which does not interact with the TPPTS and the methylated γ‐cyclodextrin which can weakly bind to the TPPTS have no and a very low effect on the equilibria, respectively. These results explain for the first time why a decrease in the normal to branched aldehydes ratio is always observed when cyclodextrins are used as mass‐transfer agents in aqueous biphasic hydroformylation processes.     

Rhodium‐Catalyzed Tandem Isomerization/Hydroformylation of the Bio‐Sourced 10‐Undecenenitrile: Selective and Productive Catalysts for Production of Polyamide‐12 Precursor

The hydroformylation of 10‐undecenenitrile ( 1 ) – a substrate readily prepared from renewable castor oil – in the presence of rhodium‐phosphane catalysts systems is reported. The corresponding linear aldehyde ( 2 ) can be prepared in high yields and regioselectivities with a (dicarbonyl)rhodium acetoacetonate‐biphephos [Rh(acac)(CO)₂‐biphephos] catalyst. The hydroformylation process is accompanied by isomerization of 1 into internal isomers of undecenenitrile ( 1‐int ); yet, it is shown that the Rh‐biphephos catalyst effectively isomerizes back 1‐int into 1 , eventually allowing high conversions of 1 / 1‐int into 2 . Recycling of the catalyst by vacuum distillation under a controlled atmosphere was demonstrated over 4–5 runs, leading to high productivities up to 230,000 mol ( 2 )⋅mol (Rh)⁻¹ and 5,750 mol ( 2 )⋅mol (biphephos)⁻¹. Attempted recycling of the catalyst using a thermomorphic multicomponent solvent (TMS) phase‐separation procedure proved ineffective because the final product 2 and the Rh‐biphephos catalyst were always found in the same polar phase. Auto‐oxidation of the linear aldehyde 2 into the fatty 10‐cyano‐2‐methyldecanoic acid ( 5 ) proceeds readily upon exposure to air at room temperature, opening a new effective entry toward polyamide‐12.

     

Synthesis,Rhodium Complexes and Catalytic Applications of a New Water‐Soluble Triphenylphosphane‐Modified β‐Cyclodextrin

A new triphenylphosphane based on a β‐cyclodextrin skeleton (PM‐β‐CD‐OTPP) was synthesized. This ligand can be dispersed in water by using the nanoprecipitation method. Transmission electron microscopy and NMR spectroscopy showed that PM‐β‐CD‐OTPP is aggregated in water and forms a stable dispersion. Its aqueous solubility can be dramatically increased in the presence of selected water‐soluble guests by formation of inclusion complexes. Associated to a rhodium precursor, PM‐β‐CD‐OTPP is able to generate soluble rhodium species in water. In addition, NMR experiments showed that the cyclodextrin cavity remains accessible for a guest even when PM‐β‐CD‐OTPP is coordinated to rhodium. Finally, this ligand was efficient for rhodium‐catalyzed hydrogenation and hydroformylation performed in aqueous medium.     

Enhanced hydroformylation by carbon dioxide‐expanded media with soluble Rh complexes in nanofiltration membrane reactors

A novel process for continuous hydroformylation in CO₂‐expanded liquids (CXLs) is demonstrated using bulky phosphite ligands that are effectively retained in the stirred reactor by a nanofiltration membrane. The reactor is operated at 50°C with a syngas pressure of 0.6 MPa to avoid CO inhibition of reaction rate and selectivity. The nanofiltration pressure is provided by ～3.2 MPa CO₂ that expands the hydroformylation mixture and increases the H₂/CO ratio in the CXL phase resulting in enhanced turnover frequency (～340 h^?1), aldehydes selectivity (>90%) and high regioselectivity (n/i ～8) at nearly steady operation. The use of pressurized CO₂ also reduces the viscosity in the CXL phase, thereby improving the mass‐transfer properties. Constant permeate flux is maintained during the 50 h run with Rh leakage being less than 0.5 ppm. This technology concept has potential applications in homogeneous catalytic processes to improve resource utilization and catalyst containment for practical viability. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4287–4296, 2013     

Rhodium‐catalyzed hydroformylation of unsaturated fatty esters in aqueous media assisted by activated carbon

Concerns about the environmental impact of chemical transformations prompted chemists to develop clean chemical processes using water as a solvent. Although appropriate for small partially water‐soluble molecules, these processes do not allow for the transformation of hydrophobic substrates due to the mass transfer limitation between the aqueous and the organic phase. In this context, we show that activated carbons can be used as mass transfer additives to promote the rhodium‐catalyzed hydroformylation of methyl oleate and other unsaturated olefins. Due to its mesoporous and hydrophobic character, the Nuchar®WV‐B activated carbon proved to be especially effective as mass transfer promoter. Actually, a significant increase in the conversion was observed. Additionally, more than 90% aldehydes were formed during the course of the reaction. When compared to other mass transfer promoters such as co‐solvents or cyclodextrins, Nuchar®WV‐B was by far the most efficient. Thus, the use of activated carbons appeared to be a suitable solution for the aqueous rhodium‐catalyzed hydroformylation of hydrophobic bio‐sourced substrates. Practical applications: The easiness with which the FAME hydroformylation could be implemented in water using activated carbons as mass transfer promoters is a major advantage in a context of an industrial–environmental approach. This finding is of importance as the obtained oxo‐products can be used in many industrial areas such as surfactants, polymers, or lubricants.     

Micellar Effects in Olefin Hydroformylation Catalysed by Neutral,Calix[4]arene‐Diphosphite Rhodium Complexes

The combination of calixarene‐derived surfactants and neutral rhodium complexes containing a hemispherical “1,3‐calix‐diphosphite” ligand led to efficient catalysts for the hydroformylation of octene and other olefins in water. While the surfactants allowed the formation of micelles that dissolve both the catalyst and the alkene, thereby resulting in high olefin:rhodium ratios, the diphosphite provided a tight envelope about the catalytic centre able to drive the reaction towards the linear aldehydes. Best results in the hydroformylation of 1‐octene were obtained when using [tetra(p‐sulfonato)]‐(tetra‐n‐butoxy)‐calix[4]arene as surfactant. With this additive remarkable linear to branched aldehyde ratios of up to 62 were obtained, the corresponding activities being higher than those observed when operating in an organic solvent [turnover frequencies (TOFs) up to 630 mol(converted 1‐octene)⋅ mol(Rh)⁻¹⋅h⁻¹].     

Rhodium‐Catalyzed Asymmetric Hydroformylation of 1,1‐Disubstituted Allylphthalimides: A Catalytic Route to β3‐Amino Acids

The high enantioselective rhodium‐catalyzed hydroformylation of 1,1‐disubstituted allylphthalimides has been developed. By employing chiral ligand 1,2‐bis[(2S,5S)‐2,5‐diphenylphospholano]ethane [(S,S)‐Ph‐BPE], a series of β³‐aminoaldehydes can be prepared with up to 95% enantioselectivity. This asymmetric procedure provides an efficient alternative route to prepare chiral β³‐amino acids and alcohols.