Mechanism Of Hydroformylation Research Articles

Novel fragrant aldehydes from (1R,5R)-sabinene: An experimental study supported by DFT calculations revealing an unusual hydroformylation mechanism

The fragrance industry continually searches for compounds that introduce new scent notes or improve existing ones. Herein, we report a methodology for obtaining two novel aldehydes, potentially interesting for application in fragrance formulations, via rhodium-catalyzed hydroformylation of (1R,5R)-sabinene, a biorenewable monoterpene available in many essential oils. One of the aldehydes, which retained the original sabinene skeleton, was derived from the hydroformylation of the exocyclic C-C double bond through the accepted hydroformylation mechanism. The other aldehyde arose from the interaction of rhodium with the cyclopropane ring through an unusual mechanism, which resulted in the cyclopropane ring cleavage, forming a product that shares structural similarities with established fragrant molecules. The selectivity was controlled by adjusting the reaction conditions (temperature, pressure, P-ligand, and P/Rh ratio). Each aldehyde was obtained in a 70–80 % yield, depending on the reaction conditions. Combining our experimental findings with DFT calculations allowed us to propose an unusual hydroformylation reaction mechanism involving cyclopropane moiety in vinylcyclopropanes.

Unravelling structure sensitivity in heterogeneous hydroformylation of aldehyde over Rh

Delineating the geometrical and electronic structure of supported metal is significant for developing heterogeneous hydroformylation catalysts. This study modulated the configuration and charge distribution of Rh to construct highly efficient Rh@SiO2 catalysts for formaldehyde hydroformylation. The structure sensitivity of Rh species reveals that single-atom Rh can solely catalyze hydrogenation, while Rh aggregates are active for hydroformylation. Moderate Rh nanoclusters (0.98 nm) offered the highest TOF (183 h−1) and selectivity (90.8 %) of glycolaldehyde. Electronic effects demonstrate that synergy between Rh0 and Rh+ sites on the cluster is essential to enhancing the reaction. The Rh0 species function as the adsorption/activation sites for H2 and formaldehyde, and the Rh+ sites act to coordinate PPh3 and CO to form Rhδ+(CO)x(PPh3)y active species. This study provides new insights into the design of heterogeneous catalysts and guidance for understanding the structure sensitivity of active metal and hydroformylation mechanism.

Rhodium-Catalyzed Chemo-, Regio- and Enantioselective Hydroformylation of Cyclopropyl-Functionalized Trisubstituted Alkenes.

The first rhodium-catalyzed highly chemo-, regio- and enantioselective hydroformylation of cyclopropyl-functionalized trisubstituted alkenes affording useful chiral cyclopropyl entities is reported. Compared to generally used diphosphine ligands for asymmetric catalysis, the modified hybrid phosphorus ligand, named (R,S)-DTBM-Yanphos, can convert a series of readily available cyclopropyl-functionalized trisubstituted alkenes into high-value chiral cyclopropyl-functionalized aldehydes with high selectivities (81-98 % ee). Gram-scale reactions (TON up to 1500) and follow-up transformations to the corresponding alcohol, acid, esters and nitrile are also presented. Finally, a possible hydroformylation mechanism involving ring-open-hydroformylation pathways is proposed based on control and deuteroformylation reactions.

Rhodium‐Catalyzed Chemo‐, Regio‐ and Enantioselective Hydroformylation of Cyclopropyl‐Functionalized Trisubstituted Alkenes

The first rhodium-catalyzed highly chemo-, regio- and enantioselective hydroformylation of cyclopropyl-functionalized trisubstituted alkenes affording useful chiral cyclopropyl entities was reported. Compared to generally used diphosphine ligands for asymmetric catalysis, the modified hybrid phosphorus ligand, named (R,S)-DTBM-Yanphos, can convert a series of readily available cyclopropyl-functionalized trisubstituted alkenes to high-value chiral cyclopropyl-functionalized aldehydes with high selectivities (81-98% ee). Gram-scale reaction (TON up to 1,500) and follow-up transformations to the corresponding alcohol, acid, esters and nitrile were also presented. Finally, a possible hydroformylation mechanism involving ring-open-hydroformylation pathways was proposed as evidenced by control and deuteroformylation reactions.

The catalytic mechanism of hydroformylation of 1-butene on rhodium-coordinated organic linkers in MOFs: A computational study

In this work, five different ligands for MOFs catalyzing 1-butene hydroformylation reactions were investigated using density functional theory (DFT) with heteroatoms (N, O, P) containing in the organic ligands that can chelate the catalytic metal Rh. The results show that the N/P-containing organic linkers have lower activation barriers than the carboxylate linkers (O-containing) and have potential for catalytic hydroformylation reactions. However, the N-containing catalysts have a significant defect in the selectivity of linear/branched product. The relatively low regioselectivity may be due to their weak steric effect of ligands. This work explores the strategy that MOFs fixing the single metal atom at metallolinkers for catalytic hydroformylation of 1-butene. It is of great significance for the design and construction of MOFs for hydroformylation in the future investigation.

Insight into decomposition of formic acid to syngas required for Rh-catalyzed hydroformylation of olefins

Formic acid (FA) is one kind of important bulk chemicals, which is recognized as a sustainable and eco-friendly energy carrier to transport H2 via dehydrogenation or CO via decarbonylation. Expectantly, FA upon decomposition into H2 and CO could be used as the syngas alternative for hydroformylation. In this paper, the behaviors of FA to release H2 as well as CO following the distinct pathways were carefully investigated for the first time, and then established a new hydroformylation protocol free of syngas. It was found that the atmospheric hydroformylation of olefins with formic acid (FA) as syngas alternative was smoothly fulfilled over Xantphos (L1) modified Rh-catalyst under mild conditions (80 °C, Rh concentration 1 mol %, 14 h), resulting in >90% conversion of the olefins along with the high selectivity to the target aldehydes (>93%). By using FA as syngas source, the side-reaction of olefin-hydrogenation was greatly depressed. The in situ FT-IR and the high-pressure 1H NMR spectroscopic analyses were applied to reveal how FA behaves dually as CO surrogate and hydrogen source over L1-Rh(acac)(CO)2 catalytic system, based on which the deeply insight into the catalytic mechanism of hydroformylation of olefins with FA as syngas alternative was offered.

Kinetics of 1‐decene hydroformylation in an aqueous biphasic medium using a water‐soluble Rh‐sulfoxantphos catalyst in the presence of a cosolvent

AbstractThe kinetics of hydroformylation of 1‐decene has been studied in an aqueous biphasic medium using a water‐soluble Rh‐sulfoxantphos catalyst in the presence of N‐methyl pyrrolidone as a cosolvent at 383‐403 K. The rate was found to be first order, with concentrations of catalyst and olefin and partial order, with concentrations of hydrogen in the liquid phase. The plot of rate versus excess ligand and CO concentrations passed through maxima, indicating negative order dependence at higher concentrations. These trends have been interpreted based on the established hydroformylation mechanism. High selectivity towards the linear aldehyde was maintained (n: iso ratio > 30). An empirical rate equation has been proposed which was found to be in good agreement with the observed rate data within the experimental error. The activation energy was evaluated to be 74.76 kJ/mol.

Computational Modelling of Selectivity in Cobalt-Catalyzed Propene Hydroformylation.

A mechanistic model for the cobalt-catalyzed hydroformylation of propene, based on density functional theory and coupled cluster electronic structure calculations and transition state theory, is proposed to explain the experimentally observed reactivity and selectivity. The electronic structure calculations provide very accurate energies, which are used with transition state theory to compute rate constants; the kinetics of the network of coupled reactions are then modelled numerically for this organometallic reaction. The model accounts well for the dependence of rate on the concentrations of catalysts and reagents, and also on the temperature, and the agreement with experiment is improved still further upon making small adjustments to the ab initio calculated free energy values. The calculations provide detailed kinetic insight into the mechanism of hydroformylation and the role of various elementary steps in defining reactivity and selectivity.

Kinetics and mechanisms of homogeneous catalytic reactions: Part 15. Regio-specific hydroformylation of limonene catalysed by rhodium complexes of phosphine ligands

Limonene hydroformylation was studied in the presence of Rh-based catalytic systems, which were prepared in situ by addition of three equivalents of PPh3, one of 1,2-bis(diphenylphosphino)ethane (dppe), or one of 1,1,1-tris(diphenylphosphino)ethane (triphos) to Rh(CO)2(acac) (1). These systems were efficient precatalysts for the target reaction, generating limonenal regio-specifically under mild reaction conditions (80 °C and 20 atm of syngas). The found activity order was: (1)/3 PPh3 > (1)/triphos > (1)/dppe. The active catalytic species are proposed to be square planar hydrido-carbonyl complexes containing two phosphorus atoms coordinated at the rhodium centre. A kinetic study of this reaction catalysed by (1)/3 PPh3, the most active catalytic system, allowed us to propose that the mechanism of hydroformylation of limonene is similar to those reported for other olefins using RhH(CO)(PPh3)3 or Rh systems containing either dppe or triphos as precatalysts.

Kinetic and Mechanisms of the Aqueous-Biphasic Hydroformylation of Olefins Contained in Naphtha Cuts Catalyzed by RhH(CO)(TPPTS)3 [TPPTS: Tri(sodium m-sulfonated-phenyl)phosphine

A kinetic study of the individual olefins present in naphtha, their mixture (synthetic naphtha) and the olefins present in a real naphtha was carried out using RhH(CO)(TPPTS)3 [TPPTS: tri(sodium m-sulfonated-phenyl)phosphine] as the catalyst precursor in aqueous-biphasic medium (toluene/water or naphtha/water), under mild reaction conditions: 80 °C, 800 psi (55.4 atm) and 600 rpm. The study consisted in the characterization of real naphtha, the selection of the model olefins, the preparation of synthetic naphtha, followed by hydroformylation of the individual olefins, of the olefin mixture and of a real naphtha cut. For 1-hexene aqueous-biphasic reaction, a kinetic study based on initial rate method showed a first order dependence on catalyst, substrate and dissolved hydrogen concentrations, whereas a fractional order was observed for carbon monoxide concentration. This kinetic results are in accord with the traditional hydroformylation mechanism, the hydrogenolysis of rhodium-acyl species being the rate-determining step of the cycle. From all the reaction profiles, it was corroborated by using the integral method that the dependence with respect to the olefin concentration was of first order for the aqueous-biphasic hydroformylation of individual olefins and their mixture, as well as for the olefins present in real naphtha cut. These results are important because of knowing the kinetics and mechanisms of the hydroformylation of the olefins present in naphtha, it is possible to improve the activity of the precatalyst and/or to design new ones for this type of application, i.e. the improving of the fuel quality through the green technology of aqueous-biphasic catalysis. A kinetic study of the individual olefins present in naphthas, their mixture (synthetic naphtha) and the olefins present in a real naphtha was carried out in aqueous-biphasic medium using RhH(CO)(TPPTS)3 [TPPTS = tri(sodium m-sulfonated-phenyl)phosphine] as the catalyst precursor in a aqueous-biphasic media, under mild reaction conditions: 80 °C, 800 psi (55.4 atm) and 600 rpm. The kinetic results are in accord with the traditional hydroformylation mechanism.

Kinetic studies of hydroformylation of 1-butene using homogeneous Rh/PPh3 complex catalyst

The kinetic studies of hydroformylation of 1-butene to produce pentanal were investigated by using Rh/PPh3 complex as homogeneous catalyst, valeraldehyde and its polycondensates as solvent. The experiment was carried out on small hydroformylation continuous reaction installation. The effects of reaction temperature, the concentration of 1-butene, the partial pressure of CO or H2 and the concentration of rhodium of catalyst on the reaction rate were studied. Based on the reaction mechanism of hydroformylation and the latest research results of hydroformylation kinetics, the kinetic equation suitable for the hydroformylation of 1-butene was established. The parameters of the kinetic equation were regressed and verified with the experimental data. The relationship between the normal/isomeric ratio of pentanal and the partial pressure of CO was further explored.

Richard F. Heck (1931-2015).

Richard F. Heck (1931-2015).

Mechanistic investigation of platinum-catalysed hydroformylation of propene: A density functional study

The mechanism of hydroformylation of propene in the presence of both cis-PtH(SnCl 3)(PH 3) 2 and trans-PtH(SnCl 3)(PH 3) 2 catalysts has been investigated. A density functional study has been carried out for all of the elementary steps of the catalytic cycle, i.e. for the alkene coordination, for its insertion into the Pt–H bond, carbon monoxide activation and its subsequent insertion into the Pt–alkyl bond. Finally, the product forming step, the dihydrogen activation and aldehyde elimination have been investigated. It has been found that the regioselectivity of hydroformylation is determined in the olefin insertion step. The computed ratio of the linear regioisomer, n-butanal is predicted to be 83% when solvation corrections were employed, being in very good agreement with the experimental result. Among the elementary steps the hydrogenolysis has been found to be the slowest followed by the migratory carbon monoxide insertion step. Due to the crucial role of the trichlorostannato ligand the electronic effects of SnCl 3 has been analysed employing the charge decomposition analysis (CDA), the natural bond orbital (NBO) and the atoms in molecules (AIM) methods.

Investigations on the kinetics of hydroformylation of 1-hexene using HRh(CO)(PPh 3) 3 encapsulated hexagonal mesoporous silica as a heterogeneous catalyst

Kinetics of HRh(CO)(PPh 3) 3 encapsulated in hexagonal mesoporous silica has been investigated for the heterogeneous catalyzed hydroformylation of 1-hexene. The rates of hydroformylation of C 5–C 12 alkenes, determined under identical conditions, indicated a decreasing trend on increasing the chain length of the alkenes. The representative alkene, 1-hexene has been subjected for detail kinetic investigations. The 1-hexene hydroformylation kinetics has been studied as the function of the amount of catalyst, concentration of 1-hexene, partial pressure of CO and H 2, and temperature. All these parameters were found to influence the rate of hydroformylation. The rate was observed to be first order with respect to partial pressure of hydrogen. The rate was observed to increase with the increase in the amount of the catalyst and approached saturation on increasing the catalyst amount. Rates increased on increasing the CO pressure and 1-hexene concentration up to certain values, and on further increasing these parameters, substrate inhibited kinetics was observed for both CO and 1-hexene at higher pressures and concentrations, respectively. A kinetic rate model based on the mechanism of hydroformylation of 1-hexene was found to fit with the experimental rate with ±15% deviation.

Theoretical Study on Mechanism of Hydroformylation of Ethene Catalyzed by a Heterobimetallic Rh(I)‐Cr Complex

Abstract The mechanism of ethene hydroformylation catalyzed by a heterobimetallic complex HRh(CO)(PH3)(µ‐PH2)2‐ Cr(CO)4 was investigated by density functional theory (DFT). Both the associative and dissociative mechanisms were studied, and the results were compared. It was found that the introduction of Cr(CO)4 moiety did not remodel the mechanism of hydroformylation of simple alkenes. The dissociative mechanism is predominant. The carbonyl insertion is the rate‐limiting step for the whole catalytic cycle with a free energy barrier of 91.15 kJ/mol at 298.15 K and 101.325 kPa. The aldehyde elimination step was predicted to be irreversible. These results are in good agreement with the previous theoretical and experimental studies.

Comprehensive Theoretical Study on the Mechanism of Regioselective Hydroformylation of Phosphinobutene Catalyzed by a Heterobinuclear Rhodium(I)−Chromium Complex

A concerted mechanism for the hydroformylation of phosphinobutene catalyzed by the heterobinuclear complex (CO)4Cr(μ-PH2)2RhH(CO)(PH3) was elucidated by density functional theory (DFT), with particular emphasis on the catalytic cycle, the regioselectivity, the cooperativity of Cr with Rh, and the interpretation of experimental observations. Four possible mechanisms were investigated, and the results were compared. It is found that the introduction of the Cr(CO)4 moiety remodels the mechanism. The Rh−Cr-catalzyed hydroformylation mechanism includes the following: (a) formation of the chelate acyl species through a chelate associative mechanism including olefin addition, olefin insertion, and carbonyl insertion steps, (b) CO addition to the chelate acyl species with the formation of a monodentate acyl species, and (c) the conversion of the monodentate acyl species to the product aldehyde through H2 coordination, H2 oxidative addition, and aldehyde elimination. Carbonyl insertion is predicted to be the rate-limiting step, with a free energy barrier of 86.76 kJ/mol in benzene solution at 353.15 K and 27.15 atm. The favorability of the branched product is predicted to be nearly 100% both kinetically and thermodynamically. The chromium serves as an orbital reservoir in olefin addition and insertion steps via the variation of the orbital interaction between Rh and Cr atoms. The catalytic activity of the Rh(I)−Cr bimetallic complex is higher than that of the monometallic Rh catalysts. These could explain satisfactorily the reported experimental observations.

A theoretical study on chemo- and regioselective Rh-catalyzed hydroformylation and hydrogenation of propyne

A comprehensive theoretical investigation on the mechanism of hydroformylation and hydrogenation of propyne catalyzed by the modified catalyst HRh(CO) 2(PH 3) is carried out employing a nonlocal density functional method (B3LYP). There are a number of possible pathways for this catalytic cycle. It comes to the conclusion from computation that the propyne insertion into Rh–H bond step is irreversible and thus the regioselectivity-limiting step for the whole catalytic cycle. The results from calculation indicate that the energy barrier for hydroformylation of propyne is obviously lower than that of hydrogenation, so hydroformylation of propyne could be easier than propyne hydrogenation. The main product is trans-butenal originated from hydroformylation and can be further hydrogenated to give birth to butanal at last.

Branched Selective Hydroformylation: A Useful Tool for Organic Synthesis

Hydroformylation reactions that show branched regioselectivity are reviewed. The mechanism of hydroformylation and the current state of the art in linear selective hydroformylation is briefly discussed prior to a more in depth discussion on synthetically useful branched selective hydroformylation reactions. The review divides these into several different classes; hydroformylation of internal cyclic alkenes, acyclic internal alkenes, aryl alkenes, terminal alkenes bearing electron withdrawing groups, terminal alkenes bearing groups that can potentially co-ordinate to the rhodium catalysts, and simple terminal alkenes. Recent advances in asymmetric hydroformylation are also discussed. The review aims to provide the non-specialist and expert reader with the information required to assess the type of substrate, catalyst and reaction conditions that are likely to be conducive to obtaining branched aldehydes in a hydroformylation reaction.

Computational experiment on hydroformylation and hydrogenation of ethyne catalyzed by Rh complex: a competitive study

A comprehensive theoretical investigation on the mechanism of hydroformylation and hydrogenation of ethyne by the rhodium catalyst at employing a nonlocal density functional method (B3LYP) and Møller–Plesset correlation energy correction at second-order, MP2 level independently. We have explored all critical elementary steps for the whole catalytic cycle, namely, the hydrogenation and hydroformylation of ethyne. There were a number of possible pathways for this catalytic cycle, originating from the ethyne association with catalyst. It came to the conclusion from computation that the acetenyl insertion into Rh–H bond was irreversible and the rate-limiting step for the whole catalytic cycle. It indicated that the energy barrier for hydrogenation of ethyne was obviously lower than that for hydroformylation so hydrogenation of ethyne could be easier than ethyne hydroformylation. The main product was olefin from hydrogenation that can be further hydroformylation to give birth to propanaldehyde at last. The other product was acrolein from hydroformylation.

(5 R)-5-Alkyl-5,6-dihydroindolizines via stereospecific domino hydroformylation/cyclodehydration of (3 R)-3-(pyrrol-1-yl)alk-1-enes

(5 R)-5-Alkyl-5,6-dihydroindolizines 3a– c having the same high enantiomeric excess (>92%) as the corresponding starting olefins (3 R)-3-(pyrrol-1-yl)alk-1-enes 1a– c were obtained via a highly regioselective and stereospecific domino hydroformylation/cyclodehydration reaction sequence. The reasons for this configurational stability were also analyzed in the light of the general accepted rhodium catalyzed hydroformylation mechanism.