Hydroformylation Of Styrene Research Articles

P(V)-Promoted Rh-Catalyzed Highly Regioselective Hydroformylation of Styrenes under Mild Conditions.

Hydroformylation of olefins is widely used in the chemical industry due to its versatility and the ability to produce valuable aldehydes with 100% atom economy. Herein, a hybrid phosphate promoter was found to efficiently promote rhodium-catalyzed hydroformylation of styrenes under remarkably mild conditions with high regioselectivities. Preliminary mechanistic studies revealed that the weak coordination between the Rhodium and the P=O double bond of this pentavalent phosphate likely induced exceptional reactivity and high ratios of branched aldehydes to linear products.

Understanding support effects on Rh2P catalyzed styrene hydroformylation by combining characterizations and kinetics

Styrene hydroformylation over Rh2P loaded on different oxides was compared to investigate support effects on catalytic performance. The electron density of Rh was probed by CO-DRIFTS, and the acid-base properties of the catalysts were detected by NH3- and CO2-TPD. Rh2P had higher electron density when loaded on basic supports, and n-type semiconductor showed additional electron donation effects compared to isolators. A kinetics model was established to identify hydrogen addition as the rate-determining step, and the changes in rate constant and adsorption equilibrium with different supports were compared. Electron donation from the supports was found to promote the activity of Rh2P via weakening styrene and aldehyde adsorption and facilitating hydrogen addition. The advantage of using CeO2 (i.e., basic oxide with n-type semiconductivity) as the support was suggested.

Regioselectivity Inversion in Hydroformylation of Aryl Alkenes with a Diphosphoramidite-rhodium Catalyst

Abstract: Rhodium catalysts for hydroformylation of aryl alkenes generally promote the formation of branched aldehydes. Here, we have demonstrated that by using a single rhodium catalyst containing a diphosphoramidite ligand derived from BINOL, it is possible to achieve the inversion of regioselectivity in the hydroformylation of aryl alkenes simply by reducing the syngas pressure or, alternatively, increasing the reaction temperature. Indeed, the hydroformylation of styrene carried out at 20 bar and 50°C resulted in 72% of 2- phenylpropanal, while at atmospheric pressure, 71% of 3-phenylpropanal was obtained. A similar linear selectivity (72-74%) was observed when the hydroformylation of styrene, pmethylstyrene, and p-methoxystyrene was performed at 10 bar and higher temperature (80°C). The regioselectivity of the hydroformylation of trans-β-methylstyrene under mild conditions (80°C, 10-20 bar) was also strongly influenced by the syngas pressure. The results of this study show that it is possible to reverse the selectivity of aryl alkenes hydroformylation with a single catalyst by simply exploring the reaction conditions. In this paper, we have shown that the inversion of the regioselectivity in the hydroformylation of aryl alkenes can be achieved using a single rhodium catalyst containing a BINOL-derived diphosphoramidite ligand by reducing the syngas pressure or, alternatively, increasing the reaction temperature.

Heteroleptic dirhodium(II,II) acetato-bipyridyl complexes: Evaluation as catalyst precursors for hydroformylation reactions

The synthesis of cationic bimetallic ‘pseudo-paddlewheel’ dirhodium(II,II) acetato-bipyridyl complexes of the type [Rh2(OAc)2(bis-4,4′-R-bipy)2]2+ containing either acetate (AcO-) or hexafluorophosphate (PF6-) counter ions is described. In both series, the 4 and 4′ positions of each bipyridyl ligand are substituted such that R = H, CF3 or OMe (complexes 1-3 for AcO- and 4-6 for PF6- derivatives). As catalyst precursors for the hydroformylation reaction, the complexes were initially evaluated using 1-octene as a substrate. The complex which displayed the greatest chemoselectivity toward aldehydes was evaluated further as a catalyst precursor for the hydroformylation of styrene, cyclohexene and 7-tetradecene as substrates. A correlation between product distributions in terms of chemo- and regioselectivity in the hydroformylation reaction versus axial site interaction is delineated. Recyclability was achieved through suitable modification of the substituent and counter ion, culminating in a simplistic method of post-catalytic precursor collection with minimal reduction of the catalytic activity over 5 cycles.

Rh nanoparticles supported on porous hexagonal boron nitride nanorods with hierarchical structure for highly efficient hydroformylation of olefins

Hydroformylation would be a promising alternative for partial technological process in petrochemical industry because it is a 100% atom-economical route for large-scale production of aldehydes and alcohols from olefins and synthesis gas (H2 and CO). However, there are still a few problems such as cost-intensive recycling and harsh operating conditions etc. encountering in the ligand-modified cobalt and rhodium as homogeneous catalysts in practical applications. Responding to the challenges, to exploit heterogeneous catalysts especially supported catalysts is desired and needs to make more efforts. Here, porous boron nitride (p-BN) with hierarchical structure is designed through a facile thermal polymerization procedure for catalyst support. The p-BN possesses nanorod morphology assembled by numerous highly crystallized hexagonal boron nitride (h-BN) nanoparticles with the diameter of about 20 nm as building blocks, thereby forming abundant interparticle pores. The Rh nanoparticles are then supported on p-BN by an impregnation-borohydride reduction method using RhCl3 as metal precursor, and the obtained catalyst of Rh nanoparticle supported on p-BN (Rh/p-BN) is applied in hydroformylation of styrene. The high porosity and accessible boron acid sites arising from hierarchical structure of p-BN nanorods make Rh nanoparticles homogeneously disperse on the surface of p-BN nanorods and also keep the diameter about 5 nm without further aggregations. Just for this reason, Rh/p-BN exhibits excellent activity of styrene hydroformylation with the highest turnover frequency of styrene as high as 12000 h−1, in comparison with other supported catalysts using different catalyst supports. Besides the detailed investigation of the catalytic properties of Rh/p-BN under different reaction conditions, the recycle of Rh/p-BN is also conducted for five times during which there is no significant decrease in catalytic activity. The present findings indicates that the combination of catalyst support of p-BN and metal nanoparticle catalysts could be an attractive strategy for designing heterogeneous hydroformylation catalysts.

Phosphorus-Doped Carbon-Supported Rh Nanoparticles for the Hydroformylation of Styrene with High Regioselectivity

Rhodium nanoparticles supported on phosphorus-doped carbon (Rh/PC) are successfully prepared by the ball-milling method with sodium hypophosphite as the phosphorus source. The catalyst exhibits superb conversion (93.6%) and high regioselectivity (branched aldehydes/linear aldehydes = 20.2:1) for the hydroformylation of styrene compared to the phosphorus-free (Rh/C) and metal-free (PC) catalysts.

Hydroformylation over polyoxometalates supported single-atom Rh catalysts

Atomic dispersion of Rh on phosphotungstic acid (PTA) salts was achieved by a self-assembled precipitation method using alkali metal ions as coprecipitation reagents. During styrene hydroformylation, the supported Rh single-atom catalyst (Rh1/M-PTA, M refers to an alkali metal ion) demonstrated an optimum turnover frequency (TOF) of 1076 h^-1. With increasing ionic radius, the pore size of the catalysts increased in the following order: Rh₁/K-PTA<Rh₁/Rb-PTA<Rh₁/Cs-PTA. The catalytic activity showed the same trend, suggesting a positive correlation between pore size and hydroformylation performance. Further experimental data suggested that temperature is an important factor affecting not only the activity but also the selectivity. This study enriches the understanding of the structure and catalytic properties of PTA-supported single-atom materials. The cation-controlled synthesis of catalysts may also be applied to prepare other single-atom catalysts with tunable pore size distributions.

Amino functionalized SBA-15 Loaded Rh Catalyst for Asymmetric Hydroformylation of Styrene

A recoverable Rh/N-SBA-15 heterogeneous catalyst for asymmetric hydroformylation of styrene was prepared by post grafting method. XRD, TG, 29Si MAS NMR and ICP characterization, revealed that the introduction of amino silane and RhCl3 had no adverse influence on the ordered mesoporous structure of the support. The Rh/N-SBA-15 catalyst was proved to be highly efficacious and stable for asymmetric hydroformylation of styrene. The experimental results demonstrated that amino silane improved the loading capacity of SBA-15 to RhCl3, and thereby improved its catalytic performance. The high efficiency and recyclability of Rh/N-SBA-15 catalyst demonstrated its great potential for application in asymmetric hydroformylation reactions.

Highly dispersed Rh single atoms over graphitic carbon nitride as a robust catalyst for the hydroformylation reaction.

Rhodium-catalysed hydroformylation, effective tool in bulk and fine-chemical synthesis, predominantly uses soluble metal complexes. For that reason, the metal leaching and the catalyst recycling are still the major drawbacks of this process. Single-atom catalysts have emerged as a powerful tool to combine the advantages of both homogeneous and heterogeneous catalysts. Since using an appropriate support material is key to create stable, finely dispersed, single-atom catalysts, here we show that Rh atoms anchored on graphitic carbon nitride are robust catalysts for the hydroformylation reaction of styrene.

Synthesis of P-stereogenic 1-phosphanorbornane-derived phosphine-phosphite ligands and application in asymmetric catalysis.

A convenient synthesis of enantiopure mixed donor phosphine-phosphite ligands has been developed incorporating P-stereogenic phosphanorbornane and axially chiral bisnaphthols into one ligand structure. The ligands were applied in Pd-catalyzed asymmetric allylic substitution of diphenylallyl acetate, Rh-catalyzed asymmetric hydroformylation of styrene and Rh-catalyzed asymmetric hydrogenation of an acetylated dehydroamino ester. Excellent branched selectivity was observed in the hydroformylation although low ee was found. Moderate ee's of up to 60% in allylic substitution and 50% in hydrogenation were obtained using bisnaphthol-derived ligands.

Unique phosphine ligand synergy in asymmetric hydroformylation of styrene over the Rh@MOF-5 heterogeneous catalysis system

For the heterogeneous reaction of asymmetric hydroformylation (AHF), a highly decentralized active Rh site played a key role in enhancing the yield of chiral isomeric aldehydes.

Rhodium‐Catalyzed Asymmetric Hydrohydrazonemethylation of Styrenes: Access to Chiral Hydrazones, Hydrazides, Hydrazines and Amines

AbstractThe catalytic asymmetric hydroformylation of styrenes was combined with condensation of the resulting aldehydes with acetohydrazide as nucleophile leading to γ‐chiral N’‐substituted aceto‐hydrazones. This cascade reaction is called hydrohydrazonemethylation (HHM) in analogy to similar hydroformylation/condensation sequences. The catalyst was formed in situ from the commercially available chiral phosphine‐ligand (R,R)‐Ph‐BPE and [Rh(acac)(CO)2] and used at a loading of 0.2 mol%. The stable condensation products are not prone to tautomerization providing versatile chiral intermediates. Their one‐pot reduction with DMAB/TsOH resulted in the corresponding γ‐chiral N’‐substituted acetohydrazides (14 examples) with yields ranging from 73% to 91% and enantioselectivities from 77% to 97% ee. Deprotection of the acetohydrazides led to the corresponding β‐chiral hydrazines. Reduction and hydrogenolysis of the hydrazones over Raney‐Ni yielded the corresponding β‐chiral primary amines with 95% ee. Diastereoselective functionalization of the C=N bond of the hydrazones is a further synthetic option, as demonstrated by allylation with (allyl)SiCl3.magnified image

Ultralow-Loading and High-Performing Ionic Liquid-Immobilizing Rhodium Single-Atom Catalysts for Hydroformylation.

We have developed a Keggin polyoxometalate (POM)-based ionic-liquid (IL)-immobilizing rhodium single-atom Rh catalyst (MTOA)5 [SiW11 O39 Rh] (MOTA=methyltrioctylammonium cation) that can afford exceptionally high catalytic activity for the hydroformylation of alkenes to produce aldehydes at an ultralow loading of Rh (ca. 3 ppm). For styrene hydroformylation, both the conversion and the yield of the aldehyde can reach almost 99 %, and a TOF as high as 9000 h-1 was obtained without using any phosphine ligand in the reaction process. Further characterization by FTIR, ICP and ESI-MS analysis revealed that the single Rh atom was incorporated in the lacunary POM anions. In particular, the bulky IL cation can play an additional role in stabilizing Rh species and thus prevent aggregation and leaching of Rh species. The IL catalyst was miscible with n-hexane at temperatures; this contributed to exceptionally high activity for hydroformylation even at ultra-low loading of IL catalyst.

Metal–organic framework ZIF-8 loaded with rhodium nanoparticles as a catalyst for hydroformylation

Porous metal–organic framework ZIF-8 materials containing incorporated rhodium (Rh@ZIF-8) and rhodium chloride (RhCl3@ZIF-8) nanoparticles were obtained and tested as a catalytic reaction vessel in the reactions of hydroformylation of 1-decene and styrene. Catalytic tests with Rh@ZIF-8 showed that the selectivity and conversion of the hydroformylation reaction depended on the size of the substrate molecule. The incorporation of catalytic nanoparticles into the pores of a metal–organic framework opens up new possibilities for regioselective hydroformylation.

Regioselectivity regulation of styrene hydroformylation over Rh-based Phosphides: Combination of DFT calculations and kinetic studies

Heterogeneous hydroformylation catalysts have attracted much attention to overcome the separation challenges of homogeneous systems. Herein, we proposed a semi-theoretical model to predict the apparent activity and regioselectivity over Rh-based phosphide catalysts. The density functional theory (DFT) calculations were conducted to understand the surface reaction mechanism and to determine the rate determining step (RDS) to either linear or branched aldehydes. The kinetic expressions were further studied based on equilibrium hypothesis using the information of RDS obtained from DFT calculations. The semi-theoretical model was verified by condition experiments. Using this model, the regioselectivity of products could be effectively regulated according to production requirements by simply changing the temperature and pressure conditions. The highest selectivity to branched aldehydes reached 95% at a conversion of 98% and the corresponding TOF was 204 h−1, which was comparable with the best homogeneous Rh catalysts.

Stereoisomeric Tris-BINOL-Menthol Bulky Monophosphites: Synthesis, Characterisation and Application in Rhodium-Catalysed Hydroformylation

Four stereoisomeric monoether derivatives, based on axially chiral (R)- or (S)-BINOL bearing a chiral (+)- or (−)-neomenthyloxy group were synthesised and fully characterised by NMR spectroscopy and X-ray crystallography. The respective tris-monophosphites were thereof prepared and fully characterised. The coordination ability of the new bulky phosphites with Rh(CO)2(acac), was attested by 31P NMR, which presented a doublet in the range of δ = 120 ppm, with a 1J(103Rh-31P) coupling constant of 290 Hz. The new tris-binaphthyl phosphite ligands were further characterised by DFT computational methods, which allowed us to calculate an electronic (CEP) parameter of 2083.2 cm−1 and an extremely large cone angle of 345°, decreasing to 265° upon coordination with a metal atom. Furthermore, the monophosphites were applied as ligands in rhodium-catalysed hydroformylation of styrene, leading to complete conversions in 4 h, 100% chemoselectivity for aldehydes and up to 98% iso-regioselectivity. The Rh(I)/phosphite catalytic system was also highly active and selective in the hydroformylation of disubstituted olefins, including (E)-prop-1-en-1-ylbenzene and prop-1-en-2-ylbenzene.

Understanding the facet effects of heterogeneous Rh2P catalysts for styrene hydroformylation

Rh2P (111) facets are much more active than the other facets for heterogeneous hydroformylation.

Intermetallic Nanocatalyst for Highly Active Heterogeneous Hydroformylation.

Hydroformylation is an imperative chemical process traditionally catalyzed by homogeneous catalysts. Designing a heterogeneous catalyst with high activity and selectivity in hydroformylation is challenging but essential to allow the convenient separation and recycling of precious catalysts. Here, we report the development of an outstanding catalyst for efficient heterogeneous hydroformylation, RhZn intermetallic nanoparticles. In the hydroformylation of styrene, it shows three times higher turnover frequency (3090 h-1) compared to the benchmark homogeneous Wilkinson's catalyst (966 h-1), as well as a high chemoselectivity toward aldehyde products. RhZn is active for a variety of olefin substrates and can be recycled without a significant loss of activity. Density functional theory calculations show that the RhZn surfaces reduce the binding strength of reaction intermediates and have lower hydroformylation activation energy barriers compared to pure Rh(111), leading to more favorable reaction energetics on RhZn. The calculations also predict potential catalyst design strategies to achieve high regioselectivity.

Activity Promotion of Rh8–xCoxP4 Bimetallic Phosphides in Styrene Hydroformylation: Dual Influence of Adsorption and Surface Reaction

Activity Promotion of Rh_8–<i>x</i>Co_<i>x</i>P₄ Bimetallic Phosphides in Styrene Hydroformylation: Dual Influence of Adsorption and Surface Reaction

Ionic Liquid-Stabilized Single-Atom Rh Catalyst Against Leaching

Ionic Liquid-Stabilized Single-Atom Rh Catalyst Against Leaching