Hydroformylation Reaction Research Articles

N′N′N pincer and N′N bidentate(pyrazolylpyridyl) Rh(I) complexes as catalyst precursors for hydroformylation of olefins

The industrial process of hydroformylation or the oxo process has been used for many years in the production of aldehydes from alkenes. Different metals have been used as efficient catalysts for hydroformylation, in which linear and branched aldehydes are the products obtained; therefore, the development of new catalysts for hydroformylation with high selectivity to aldehydes is important. Rhodium complexes 6–9 were synthesized using [RhCl(CO)2]2, or [RhCl(COD)]2, with either pyrazolylpyridyl N′N′N pincer ligands or a pyrazolylpyridyl N′N ligand. These complexes were then evaluated as catalyst precursors in the hydroformylation reaction using a variety of alkenes. The catalysts all showed activity in hydroformylation but the most active catalyst was methyl-substituted pyrazolyl–rhodium complex 7 following optimization of temperature, syngas pressure and amount of catalyst. Other olefinic substrates were used for hydroformylation in the presence of 7 under the optimum hydroformylation conditions. Undecene and dodecene as substrates only showed minimal formation of aldehydes with predominantly isomerization of the alkene being observed.

Kinetic evaluation of the hydroformylation of the post-metathesis product 7-tetradecene using a heterobimetallic rhodium-ferrocenyl Schiff base derived precatalyst

Reaction engineering kinetics for the hydroformylation of the post-metathesis product 7-tetradecene using a heterobimetallic rhodium-ferrocenyl Schiff base derived precatalyst was investigated with variation of reaction temperature (85–105 °C), precatalyst loading (0.25–0.52 mM), carbon monoxide partial pressures (20–40 bar) and hydrogen partial pressures (20–40 bar). The experimental product-time distributions for the parallel hydroformylation and isomerization reaction system are well described by four interdependent pseudo first-order differential mole balance equations. The effects of temperature in the Arrhenius equation, precatalyst concentration, carbon monoxide and hydrogen partial pressures have been incorporated into a phenomenological mechanism-based rate equation. The rate of hydroformylation is first order in alkene, carbon monoxide and hydrogen, with fractional dependence in precatalyst concentration. The activation energy for the hydroformylation reaction was calculated to be 62 kJ mol−1, which is comparable to that determined for the commercialized phosphorus-modified catalyst systems.

Study on Hydroformylation of Octene Catalyzed by Rhodium-Containing Functional Ionic Liquid

Because of the irreplaceable nature of hydroformylation, it has been a hot topic in recent decades. The catalyst for hydroformylation usually takes the transition metal as the center atom. However, the high price of metal restricts the large-scale industrialization of hydroformylation reaction. In this paper, a new type of 1-polyethylene glycol monomethyl ether-3-methyl imidazole rhodium ionic liquid catalyst was used to study the hydroformylation of catalytic octene. The reaction was carried out in a 75mL autoclave. The optimum reaction conditions were obtained by experiments: when the reaction time was 5h, the reaction pressure was 4MPa, and the reaction temperature was 100°C, the conversion of octene reached 90.2%, and the yield of nonylaldehyde reached 70.6%. The new ionic liquid catalyst used in the reaction has the characteristics of “high temperature catalysis, low temperature phase separation”. It laid the foundation for the recovery of the catalyst.

Supported Cobalt Nanoparticles for Hydroformylation Reactions.

Hydroformylation of olefins has been studied in the presence of specific heterogeneous cobalt nanoparticles. The catalytic materials were prepared by pyrolysis of preformed cobalt complexes deposited onto different inorganic supports. Atomic absorption spectroscopy (AAS) measurements indicated a correlation of catalyst activity and cobalt leaching as well as a strong influence of the heterogeneous support on the productivity. These new, low-cost, easy-to-handle catalysts can substitute more toxic, unstable and volatile cobalt carbonyl complexes for hydroformylations on a laboratory scale.

Cofactor Controlled Encapsulation of a Rhodium Hydroformylation Catalyst

AbstractSupramolecular approaches in transition‐metal catalysis, including catalyst encapsulation, have attracted considerable attention. Compared to enzymes, supramolecular catalysts in general are less complex. Enzyme activity is often controlled by the use of smaller cofactor molecules, which is important in order to control reactivity in complex mixtures of molecules. Interested in increasing complexity and allowing control over supramolecular catalyst formation in response to external stimuli, we designed a catalytic system that only forms an efficient supramolecular complex when a small cofactor molecule is added to the solution. This in turn affects both the activity and selectivity when applied in a hydroformylation reaction. This contribution shows that catalyst encapsulation can be controlled by the addition of a cofactor, which affects crucial catalyst properties.

Cofactor Controlled Encapsulation of a Rhodium Hydroformylation Catalyst.

Supramolecular approaches in transition‐metal catalysis, including catalyst encapsulation, have attracted considerable attention. Compared to enzymes, supramolecular catalysts in general are less complex. Enzyme activity is often controlled by the use of smaller cofactor molecules, which is important in order to control reactivity in complex mixtures of molecules. Interested in increasing complexity and allowing control over supramolecular catalyst formation in response to external stimuli, we designed a catalytic system that only forms an efficient supramolecular complex when a small cofactor molecule is added to the solution. This in turn affects both the activity and selectivity when applied in a hydroformylation reaction. This contribution shows that catalyst encapsulation can be controlled by the addition of a cofactor, which affects crucial catalyst properties.

Isolable Silylene Ligands Can Boost Efficiencies and Selectivities in Metal-Mediated Catalysis.

A significant number of isolable silylenes are currently known. They have quickly developed from laboratory curiosities to useful ligands in metal-mediated homogeneous catalysis. This includes their utilization in various catalytic transformations, such as C-C cross-coupling, cyclotrimerization, hydroformylation, borylation, deuteration, hydrosilylation, amination, hydrogenation, and transfer semi-hydrogenation reactions. Recent studies suggest that the silylene ligands surpass the steering properties of their phosphine and N-heterocyclic carbene (NHC) analogues and provide excellent chemo-, regio-, and stereoselectivites. Mechanistic studies suggest that their promoted performance of metal-mediated catalytic transformations results from a strong σ-donor character along with cooperative effects of their SiII centers. This Minireview covers the most recent advances in the field.

Encapsulated liquid nano-droplets for efficient and selective biphasic hydroformylation of long-chain alkenes

Rh-TPPTS aqueous droplets were confined within hollow nanospheres, leading to enhancements of catalytic activity and aldehyde selectivity in hydroformylation reactions.

Multi-walled carbon nanotube-based composite materials as catalyst support for water-gas shift and hydroformylation reactions.

In times of depleting fossil fuel reserves, optimizing industrial catalytic reactions has become increasingly important. One possibility for optimization is the use of homogenous catalysts, which are advantageous over heterogeneous catalysts because of mild reaction conditions as well as higher selectivity and activity. A new emerging technology, supported ionic liquid phase (SILP), was developed to permanently immobilize homogeneous catalyst complexes for continuous processes. However, these SILP catalysts are unable to form freestanding supports by themselves. This study presents a new method to introduce the SILP system into a support made from multi-walled carbon nanotubes (MWCNT). In a first step, SILP catalysts were prepared for hydroformylation as well as low-temperature water–gas shift (WGS) reactions. These catalysts were integrated into freestanding microtubes formed from MWCNTs, with silica (for hydroformylation) or alumina particles (for WGS) incorporated. In hydroformylation, the activity increased significantly by around 400% when the pure MWCNT material was used as SILP support. An opposite trend was observed for WGS, where pure alumina particles exhibited the highest activity. A significant advantage of the MWCNT composite materials is the possibility to coat them with separation layers, which allows their application in membrane reactors for more efficient processes.

Using para hydrogen induced polarization to study steps in the hydroformylation reaction.

A range of iridium complexes, Ir(η3-C3H5)(CO)(PR2R')2 (1a-1e) [where 1a, PR2R' = PPh3, 1b P(p-tol)3, 1c PMePh2, 1d PMe2Ph and 1e PMe3] were synthesized and their reactivity as stoichiometric hydroformylation precursors studied. Para-hydrogen assisted NMR spectroscopy detected the following intermediates: Ir(H)2(η3-C3H5)(CO)(PR2R') (2a-e), Ir(H)2(η1-C3H5)(CO)(PR2R')2 (4d-e), Ir(H)2(η1-C3H5)(CO)2(PR2R') (10a-e), Ir(H)2(CO-C3H5)(CO)2(PR2R') (11a-c), Ir(H)2(CO-C3H7)(CO)2(PR2R') (12a-c) and Ir(H)2(CO-C3H5)(CO)(PR2R')2 (13d-e). Some of these species exist as two geometric isomers according to their multinuclear NMR characteristics. The NMR studies suggest a role for the following 16 electron species in these reactions: Ir(η3-C3H5)(CO)(PR2R'), Ir(η1-C3H5)(CO)(PR2R')2, Ir(η1-C3H5)(CO)2(PR2R'), Ir(CO-C3H5)(CO)2(PR2R'), Ir(CO-C3H7)(CO)2(PR2R') and Ir(CO-C3H5)(CO)(PR2R')2. Their role is linked to several 18 electron species in order to confirm the route by which hydroformylation and hydrogenation proceeds.

Effector enhanced enantioselective hydroformylation.

In this communication, we report rhodium DIMPhos complexes with an integrated DIM-receptor that can bind carboxylate containing effectors and their application in the rhodium catalyzed hydroformylation reaction. The binding of chiral effectors in non-chiral [Rh(DIMPhos)] catalysts does not lead to enantioselective hydroformylation, but the binding of either achiral or chiral effectors can significantly enhance the enantioselectivity induced by the chiral Rh-metal complexes. For example, the supramolecular complex [Rh]/[1S⊂L3] displays high regio- and enantioselectivity in the hydroformylation of vinyl acetate (72% ee, and b/l >99), whereas in absence of this effector the ee is around 17%.

Synthesis of tetra-pincer nickel(ii) and palladium(ii) complexes of resorcin[4]arene-octophosphinite [Res(OPR2)8] and rhodium-catalyzed regioselective hydroformylation reaction.

The condensation reaction of resorcinol with pentanal yielded resorcin[4]arene 1 which on bromination using N-bromosuccinimide at room temperature produced tetra-bromide derivative 2. The reactions of 2 with chlorodiphenylphosphine and o-phenylenephosphoro-chloridite yielded octaphosphinite 3 (hereafter referred to as octaphos) and octaphosphite 4, respectively. The reactions of 3 with Ni(COD)2 or Pd2(dba)3·CHCl3 in appropriate molar ratios yielded tetra-pincer complexes 5 and 6, respectively. The structures of both the complexes were established by single crystal X-ray diffraction studies. The resorcin[4]arene backbone adopts a boat structure in these complexes. Typically, the Rh-catalyzed hydroformylation of styrene prevalently delivers a branched (b) chiral aldehyde. A unique resorcin[4]arene skeleton based octaphos 3 was employed in the Rh-catalyzed hydroformylation of styrene. The hydroformylation of styrene with a metal to ligand ratio of 1 : 1 (M : L) was found to be regioselective, producing a linear (l) aldehyde as a major product with 100% conversion in 3 h. The l : b ratio surprisingly increased when the ortho positions of styrene were populated by methyl and chloro substituents. The hydroformylation of p-nitro styrene triggered a remarkably high linear : branched aldehyde ratio of 2.4 (71% linear aldehyde) despite its electron withdrawing nature. The highest linear selectivity of 97% (l : b ratio 27.8) was achieved in the case of 2,4,6-trimethylstyrene.

Alcohol Synthesis from CO2, H2, and Olefins over Alkali‐Promoted Au Catalysts—A Catalytic and In situ FTIR Spectroscopic Study

Au/TiO2 and Au/SiO2 catalysts containing 2 wt % Au and different amounts of K or Cs were tested for alcohol synthesis from CO2 , H2 , and C2 H4 /C3 H6 . 1-Propanol or 1-butanol/isobutanol were obtained in the presence of C2 H4 or C3 H6 . Higher yields of the corresponding alcohols were obtained over TiO2 -based catalysts in comparison with their SiO2 -based counterparts. This is caused by an enhanced ability of the TiO2 -based catalysts for CO2 activation, as concluded from in situ fourier-transform infrared (FTIR) spectroscopy and temporal analysis of products (TAP) studies. The synthesized carbonate and formate species adsorbed on the support do not hamper CO2 conversion into CO and the hydroformylation reaction. The transformation of Auδ+ to active Au0 sites proceeds during an activation procedure. As reflected by CO adsorption and scanning transmission electron microscopy, the accessible Au0 sites are influenced by the amount of alkali dopants and the support. FTIR data and TAP tests reveal a very weak interaction of C2 H4 with the catalyst, suggesting its quick reaction with CO and H2 after activation on Au0 sites to form propanol and propane.

Kinetics of hydroformylation of 1‐decene using carbon‐supported ossified HRh(CO)(TPPTS)3 catalyst

AbstractThe kinetics of hydroformylation of 1‐decene has been investigated using a carbon‐supported ossified HRh(CO)(TPPTS)3/Ba catalyst in a temperature range of 343–363 K. The effect of concentration of 1‐decene, catalyst loading, partial pressure of H2 and CO, and stirring speed on the reaction rate has been investigated. A first‐order dependence was observed for catalyst concentration and hydrogen partial pressure. The rate showed a typical case of substrate inhibition for high 1‐decene concentration. The rate varied with a linear dependence on PCO up to a CO partial pressure of 5–6 MPa in contrast to the general trends; for most of the rhodium‐phosphine catalyzed hydroformylation reactions, severe inhibition of rate is observed with an increase in CO pressure. A rate equation has been proposed, which was found to be in good agreement with the observed rate data within the limit of experimental errors. The kinetic parameters and activation energy values have been reported.

Hydrogen-Bonding-Assisted Supramolecular Metal Catalysis.

The process of catalyst screening and discovery still largely relies on traditional ligand-design approaches, which suffer from complex synthetic requirements and offer limited structural diversity. On the contrary, supramolecular chemistry offers the potential to harness multiple weak secondary interactions to deliver self-assembled catalysts with diverse structures or to orient substrates to achieve enzyme-like activity and selectivity. Herein, the application of hydrogen-bonding (H-bonding) interactions as a construction element and directing group in "supramolecular transition-metal catalysis" is critically reviewed and the current state-of-the-art in the field is presented. H-bonding interactions empower structurally simple ligands to deliver complex self-assembled catalysts, which have been found to catalyze a gamut of organic transformations, including hydroformylation, hydrogenation, and allylation reactions. As we will discuss, on many occasions, these supramolecular catalysts outperform their analogous covalently linked catalytic systems. The potential of H-bonding interactions as directing groups has recently been recognized by the scientific community and this Focus Review presents the role of hydrogen-bonding interactions in directing substrates to obtain excellent selectivities and activities in a range of catalytic transformations.

Novel rhodium on carbon catalysts for the oxidation of benzyl alcohol to benzaldehyde: A study of the modification of metal/support interactions by acid pre-treatments

Rhodium nanoparticles or rhodium organometallic complexes are mainly used in catalysis for reduction or hydroformylation reactions. In this work instead, we explored the capabilities of Rh nanoparticles as an oxidation catalyst, applied to the oxidation of benzyl alcohol to benzaldehyde under very mild conditions (100 °C, and atmospheric pressure) as a model reaction. Here we report the preparation of novel Rh/C catalysts by using an impregnation protocol, with particular emphasis on the pre-treatment of the carbon supports by using HNO3 and HCl, as well as the characterization of these materials by using an array of methods involving TEM, XPS and XRPD. Our preparation method led to a wide Rh particle size distribution ranging from 20 to 100 nm, and we estimate an upper limit diameter of Rh nanoparticles for their activity towards benzyl alcohol oxidation to be ca. 30 nm. Furthermore, a HNO3 pre-treatment of the activated carbon support was able to induce a smaller and narrower particle size distribution of Rh nanoparticles, whereas a HCl pre-treatment had no effect or sintered the Rh nanoparticles. We rationalise these results by HNO3 as an acid able to create new nucleation sites for Rh on the carbon surface, with the final effect of smaller nanoparticles, whereas for HCl the effect of sintering was most likely due to site blocking of the nucleation sites over the carbon surface. The roles of acid centres on the carbon surfaces for the oxidation reaction was also investigated, and the larger their amounts the larger the amounts of by-products. However, by treatment with HNO3 we were able to convert neutral or basic carbons into supports capable to enhance the catalytic activity of Rh, and yet minimised detrimental effects on the selectivity of the oxidation to benzaldehyde.

Ligand Template Strategies for Catalyst Encapsulation.

ConspectusBinding of molecules in molecular cages based on self-assembled concave building blocks has been of great interest to scientists for decades. The binding of static molecular fragments inside cage-like molecular structures is generally based on complementarity of host and guest in terms of shape and interactions. The encapsulation of homogeneous catalysts in molecular cages is of interest as activity, selectivity, and stability can be controlled by the cage as second coordination sphere, reminiscent of how enzymes control chemical reactivity. Homogeneous catalysts, however, are not static guest molecules as catalysts change in shape, charge, and polarity during the catalytic cycle, representing the challenges involved in cage controlled catalysis. To address these issues, we developed a new strategy that we coined the “ligand template approach for catalyst encapsulation”. This strategy relies on ligand building blocks that contain multiple orthogonal binding sites: the central ligand (mostly phosphorus) is bound to the transition metal required for catalysis, while other binding sites are used to construct a cage structure around the transition metal atom through self-assembly. By design, the catalyst is inside the capsule during the catalytic cycle, as the central ligand is coordinated to the catalyst. As the approach is based on a self-assembly process of building blocks, the catalyst properties can be easily modulated by modification of building blocks involved.In this Account, we elaborate on template ligand strategies for single catalyst encapsulation, based on divergent ligand templates and the extension to nanospheres with multiple metal complexes, which are formed by assembly of convergent ligand templates. Using the mononuclear approach, a variety of encapsulated catalysts can be generated, which have led to highly (enantio)selective hydroformylation reactions for encapsulated rhodium atoms. Besides the successes of encapsulated rhodium catalysts in hydroformylation, mononuclear ligand template capsules have been applied in asymmetric hydrogenation, the Heck reaction, copolymerization, gold catalyzed cyclization reactions, and hydrosilylation reactions. By changing the capsule building blocks the electronic and steric properties around the transition metal atom have successfully been modified, which translates to changes in catalyst properties. Using the convergent ligand templates, nanospheres have been generated with up to 24 complexes inside the sphere, leading to very high local concentrations of the transition metal. The effect of local concentrations was explored in gold catalyzed cyclization reactions and ruthenium catalyzed water oxidation, and for both reactions, spectacular reaction rate enhancements have been observed. This Account shows that the template ligand approach to provide catalyst in well-defined specific environments is very versatile and leads to catalyst properties that are not achievable with traditional approaches.

Expedited Screening of Active and Regioselective Catalysts for the Hydroformylation Reaction

The discovery of new homogeneous catalysts that preferentially form one product over another in regio‐ or enantioselective chemical reactions has traditionally been the province of experimental chemists. Today, computational‐based approaches have carved an increasingly important role, which, for computational catalytic designs, often rely on highly inefficient combinatorial‐based screening methods. To increase the pace of discovery, tools capable of rapidly assessing large numbers of prospective species and identify those possessing desirable properties, such as activity and selectivity, are vital. Here, through the examination of the hydroformylation of 2‐methylpropene, we demonstrate how a new tool built upon molecular volcano plots can be used to quickly predict the activity of molecular catalysts as well as estimate the intrinsic ability of each species to form one regioisomer over the other with striking accuracy. Following training and validation, these regioselective molecular volcanoes are employed to predict catalysts that preferentially form the branched product (2,2‐dimethylpropanal) in violation of Keulemans’ 70‐year‐old law. Eighteen species (out of a total of 68 predicted) were computationally predicted to have regiomeric excess (r.e.) values > 90. Overall, these tools can be used to quickly screen the activity and selectivity of potential catalysis based on two easily computed descriptor variables.

The influence of different monodentate P-ligand mixtures on Rh-catalyzed 1-butene hydroformylation

Abstract Four monodentate P-ligands and their mixtures (six groups of double-ligand systems, four groups of triple-ligand systems and one group of tetra-ligand system) were used with Rh(acac)(CO)2 (acac = acetylacetonate) or Rh(acac)CO(PPh3) as the catalyst in the hydroformylation reaction of 1-butene. It was found that different Rh catalysts showed little difference in the catalysis performance. The general order of catalysis performance is double-ligand system > single-ligand system > triple-ligand system > tetra-ligand system. Some synergistic effect in the double-ligand system was detected which needs a further investigation.

Tandem hydroformylation/aldol condensation reactions: Synthesis of unsaturated ketones from olefins

Platinum-catalysed tandem hydroformylation/aldol condensation reaction of vinyl aromatics and ketones toward the corresponding α,β-unsaturated ketones were performed under syngas atmosphere in the presence of acid co-catalysts. The in situ generated catalysts modified with various ligands proved to be efficient under applied conditions. The presence of acids promotes side reactions like hydrogenation of the alkene substrate and that of the aldehyde to the corresponding alkane and alcohol, respectively. Interestingly, the hydrogenation of the condensed products is not preferred, only trace amounts of saturated products can be detected by GC-MS. In general, moderate yields can be achieved with several ketones using styrene and α-methylstyrene as substrate in hydroformylation reaction. Linear aldehydes proved to be more active in aldol condensation step, furthermore, aromatic and cyclic ketones are also feasible coupling partners to generate the corresponding unsaturated ketones. Contrary to the preceding literature, ketones possessing α-methylene group(s) showed exclusive preference for methylene functionalization in the aldol condensation reaction.