Rate Of Hydroformylation Research Articles

Parameterization of Phosphine Ligands Modified Rh Complexes to Unravel Quantitative Structure‐Activity Relationship and Mechanistic Pathways in Hydroformylation

AbstractThis study has established the quantitative structure‐activity relationship (QSAR) model to predict formaldehyde hydroformylation activity using a class of phosphine‐Rh complexes and computational mechanistic pathway analysis. A group of computational parameters (e. g., cone angle, G‐parameter, buried volume, CO vibration frequency, NBO charge, HOMO and LUMO energy, Rh−P distance) describing the complex structural (e. g., steric and electronic) features were achieved for descriptor database of monodentate phosphine ligands. Mathematical modelling of the catalytic results with the descriptors via multivariate linear regression reveals the hydroformylation rate is principally under electronic control within the investigated ligands. Computational mechanistic analysis demonstrates significant impact of electronic feature on TOF‐determining transition state/intermediate and energetic span. The H2 distortion energy analysis elucidates the variation of energetic span of the transition states related to H2 oxidation addition, rationally accounting for the reaction outcomes.

Olefin hydroformylation and kinetic studies using mono- and trinuclear N,O-chelate rhodium(I)-aryl ether precatalysts

Rh(I)-salicylaldimine-triazole mononuclear (6) and trinuclear (7) complexes based on an aryl-ether scaffold were investigated as precatalysts in the rhodium-catalysed hydroformylation of the terminal olefin, 1-octene, and internal olefins, 7-tetradecene and 4-octene. The complexes generally show good catalytic activity in the hydroformylation of 1-octene at temperatures ranging from 75 °C to 95 °C and syngas pressures of 20 to 40 bar. The precatalysts have excellent stability and could be reused several times using organic solvent nanofiltration under optimum conditions of 85 °C and 40 bar. Kinetic studies using catalyst precursor 6 were investigated by evaluating the effect of temperature, syngas total pressure and catalyst loading on the rate of hydroformylation. The activation energy for the hydroformylation of 1-octene was calculated to be 62 kJ mol−1 and the experimental rate constants were found to be in good agreement with the predicted rate data obtained using a modified fundamental mechanism-based rate model.

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.

Rhodium-BiPhePhos catalyzed hydroformylation studied by operando FTIR spectroscopy: Catalyst activation and rate determining step

The homogeneously rhodium catalyzed hydroformylation of 1-decene was studied using operando FTIR spectroscopy. The bulky chelating diphosphite ligand BiPhePhos was used for catalyst modification. Special emphasis was given to the transformation of the Rh-precursor Rh(acac)(CO)2 to the activated HRh(BiPhePhos)(CO)2 catalyst. Under hydroformylation conditions, this complex was found to be the most abundant catalyst species over a wide range of olefin conversion. Other inactive or non-selective rhodium species were not detectable. Analysis of the turnover frequency revealed a first order dependence of the hydroformylation rate with respect to the concentration of 1-decene. These findings indicate that the coordination of the olefin to the Rh-BiPhePhos catalyst is determining the hydroformylation rate of 1-decene.

Full kinetic description of 1-octene hydroformylation in a supercritical medium

The kinetics of the hydroformylation of 1-octene in a supercritical carbon dioxide medium, catalyzed by a tris(3,5-bis[trifluoromethyl]phenyl)phosphine-modified rhodium catalyst, have been investigated. The influence of the concentration of carbon dioxide, reactants, catalyst precursors, and the reaction temperature has been determined. A kinetic model was developed, which describes the concentration-time profiles of the reactants, the linear and branched aldehydes, and the internal alkenes. Using the kinetic model activation energies for hydroformylation of 1-octene to nonanal and 2-methyloctanal were determined. Throughout the concentration ranges studied an approximate first order dependence of the hydroformylation rate on the hydrogen and catalyst concentration was found which indicated that oxidative addition of hydrogen was the rate limiting step. The increase in reaction rate and regioselectivity with an increase in ligand concentration is a striking feature of the catalyst investigated here. At higher concentrations the reaction rate was found to have a strong negative order dependence on the carbon monoxide concentration. The reaction rate had a positive order in 1-octene at a concentration lower than 0.5 mol L −1 while saturation kinetics were observed at a higher concentration. The results were explained by invoking the contribution of both monophosphine and diphosphine rhodium species to the hydroformylation catalysis.

Gas-Phase Hydroformylation of Propene over Silica-Supported PPh3-Modified Rhodium Catalysts

Heterogeneous rhodium catalysts supported on SiO2 were modified with PPh3 for the gas-phase hydroformylation of propene to produce n- and isobutanal. High selectivity to aldehydes was achieved, with no propane or alcohols formed. Investigation of the effects of reaction temperature, reactant partial pressures, total pressure, and PPh3/Rh ratio suggested that the supported catalyst behaved similarly to the homogeneous catalyst. In particular, the supported catalyst showed similar activation energies and partial and total pressure dependences of the reaction rates to those observed in homogeneous, liquid-phase reactions. The first order dependence of the hydroformylation rate on the partial pressures of propene, CO, and H2 individually led to a cubic dependence of butanal formation on total pressure for equimolar reactant mixtures. High regioselectivity with a typical n/i ratio of 14 was achieved.

Biphasic and Flow Systems Involving Water or Supercritical Fluids

Two processes are described for improving reaction rates for relatively hydrophobic substrates in aqueous biphasic systems. In the first, 1-octyl-3-methylimidazolium bromide ([Octmim]Br) increases the rate of hydroformylation of 1-octene from 8% conversion in 24 h to full conversion of 1.5 h. Phase separation is fast and catalyst retention is good. 1-Hexyl-3-methylimidazolium bromide gives little rate enhancement, whilst 1-decyl-3-methylimidazolium bromide gives stable emulsions., The mechanism of action of these additives is discussed. In the second approach, functionalising PPh3 with amidine groups allows the rhodium catalysed hydroformylation of 1-octene in toluene with a very high reaction rate. The catalyst can be switched between toluene and water by bubbling CO2 and back into toluene by bubbling N2 at 60 °C. This switching has been used to separate the catalyst from hydrophobic (from 1-octene) or hydrophilic (from allyl alcohol) aldehydes obtained from hydroformylation reactions. CO2 expanded liquids have been shown to be effective media for transporting substrates and catalysts over supported ionic liquid phase (SILP) catalysts. The advantages offered over all gas phase and liquid phase catalysts are discussed.

Regioselective and rapid hydroformylation of vinyl acetate catalyzed by rhodium complex modified bulky phosphite ligand

Abstract The regioselective hydroformylation of vinyl acetate catalyzed by rhodium complex of monodentate phosphite ligand, tri-1-naphthylphosphite P(ONp) 3 , was investigated. The P(ONp) 3 ligand exhibited a considerable impact on the rate and selectivity of hydroformylation of vinyl acetate, notably high turnover frequency (up to 11,520 h −1 ) with excellent regioselectivity (99%) to the preferred branched aldehyde and high selectivity to aldehyde (93%). Significant results with the substrate having less reactive character toward hydroformylation and practically easy accessibility of the ligand (synthesized from inexpensive compound, 1-naphthol) make this system very attractive.

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.

Rhodium complex of monodentate phosphite as a catalyst for olefins hydroformylation

Rhodium complex of a novel monodentate bulky phosphite ligand, tri-1-naphthylphosphite is studied for the hydroformylation of dissimilar alkenes specifically, 1-hexene, styrene, and cyclohexene. The steric attributes of free ligand is investigated by cone angle. The effect of concentration of alkene as well as catalyst, ligand/Rh ratio, pCO and pH 2 on the rate of reaction has been studied. For 1-hexene and styrene, the initial rate was found to be zero order with respect to initial alkene concentration and first order with respect to catalyst concentration and H 2 partial pressure. For cyclohexene, the reaction was found to be first order with respect to the initial cyclohexene concentration and of slightly positive order with respect to H 2 partial pressure. The initial rate of hydroformylation of styrene (at 80 °C, 3.0 MPa syngas pressure) is ∼3.9 times less than that of 1-hexene hydroformylation where as the rate of cyclohexene hydroformylation is ∼87 times less than that of 1-hexene hydroformylation.

Rhodium catalyzed hydroformylation of monoterpenes containing a sterically encumbered trisubstituted endocyclic double bond under mild conditions

The rhodium catalyzed hydroformylation of endocyclic monoterpenes, that is, 2-carene (1), 3-carene (2), and α-pinene (3), in the presence of PPh3 or various diphosphines and phosphites has been studied. The unmodified Rh catalyst promotes an intense isomerization of both carenes whose hydroformylation occurs rather slowly, and results in a complex mixture of aldehydes and alcohols. The addition of PPh3, diphosphines or P(OPh)3 in a P/Rh ratio as high as 20, efficiently prevents the isomerization, but the activity for hydroformylation is drastically reduced. On the other hand, the use of a bulky P(O-o-tBuPh)3 ligand both reduces the isomerization, and significantly increases the hydroformylation rate. All three sterically crowded olefins 1–3 have been efficiently hydroformylated under relatively mild reaction conditions (80–100 °C, 40–80 atm) to a main aldehyde (2-formylcarane, 4-formylcarane, and 3-formylpinene, respectively) with good chemo- and regioselectivity, and almost 100% stereoselectivity for the trans isomers.

Highly Selective Halide Anion-Promoted Palladium-Catalyzed Hydroformylation of Internal Alkenes to Linear Alcohols

Here we report on our study of the palladium-catalyzed hydroformylation of alkenes. A (bcope)Pd(OTf)2 complex (bcope = bis(cyclooctyl)phosphine ethane, 2) with substoichiometrically added halide anions is a highly efficient homogeneous catalyst (precursor) to selectively convert internal linear alkenes into predominantly linear (detergent) alcohols under mild conditions. Halide anion-dependent effects on the hydroformylation reaction rate as well as its chemo- and regioselectivity are observed. Thus, the rate of hydroformylation of thermally equilibrated internal higher alkenes increases by a factor of about 6−7 with chloride/bromide and about a factor 3−4 with iodide, while the selectivity toward alcohols increases to almost 100% upon addition of a substoichiometric quantity (with respect to palladium) of the halide anion source. Curiously, the regioselectivity toward linear alcohol increases in the reverse order, i.e., iodide > bromide > chloride. From a detailed analysis of the products obtained with model substrates, it is concluded that hydrogenolysis of (bcope)palladium-acyl intermediates is strongly accelerated by the presence of halide anions. From a comparison of the catalytic performance with some related L2Pd(OTf)2 complexes, in which L2 are bidentate phosphines closely related to bcope, it also appears that the ligand plays a critical role in the promoting effect of halide anions.

Kinetic Studies on the Hydroformylation of 1-Hexene Using RhCl(AsPh3)3 as a Catalyst

The detail kinetic study of 1-hexene hydroformylation using RhCl(AsPh3)3 as a homogeneous catalyst has been investigated. The present kinetic study involves the effect of concentrations of 1-hexene and catalyst, partial pressures of CO and H2, agitation speed, and temperature on the rate of hydroformylation. Additionally, the studies of deactivation of the catalyst RhCl(AsPh3)3 with temperature have also been done. It was observed that the rates of hydroformylation reaction were increased on increasing the initial concentrations of 1-hexene, catalyst, and partial pressures of CO and H2 at lower ranges. The activation energy was found to be 42.74 kJ/mol. A nonlinear semiempirical kinetic model was also developed to be the best fit with 11.6% error.

Influence of an additional gas on the rhodium-catalyzed hydroformylation of olefins

Abstract An additional gas such as dinitrogen, argon or xenon, present in the reaction medium in high concentration, affects the hydroformylation of cyclohexene, hex-1-ene or styrene in the presence of RhHCO(PPh3)3. The rate of hydroformylation of cyclohexene decreases as the amount of the additional gas increases: this effect may be attributed to a competition between the additional gas and one of the reagents, alkene, hydrogen or carbon monoxide for a coordinative unsaturated site available on the catalytically active intermediates. An analogous behaviour is shown when a terminal olefin (hex-1-ene or styrene) is hydroformylated in the presence of a low pressure of xenon. On the contrary, a very high pressure of dinitrogen or argon is required to show a decrease of the initial rate of the hydroformylation of the same terminal olefins. Finally, there is no or a slightly positive influence of a high pressure of helium or methane on the initial rate of the hydroformylation of the above reported olefins. This behaviour may be explained assuming an interaction between the additional gas and the rhodium catalyst.

Heterofunctionalised phosphites built on a calix[4]arene scaffold and their use in 1-octene hydroformylation. Formation of 12-membered P,O-chelate rings

The calixarene phosphites L1–L4 were obtained in high yield through reaction of PCl3/NEt3 with the monofunctionalised cone-calixarenes p-tert-butylcalix[4]arene(OH)3OR, in which the R substituents bear an oxygen donor ligand [R = CH2P(O)Ph2 (L1), CH2CO2Et (L2), CH2C(O)NEt2 (L3), CH2CH2OMe (L4)]. The calixarene core of the four ligands adopts a cone conformation and, hence, the phosphites become potential P,O-chelating systems. Phosphite L1 is remarkably stable towards aqueous NaOH, but the presence of slightly acidic water results in phosphonate formation. Slow oxidation of L1 in air afforded the corresponding mixed phosphine oxide–phosphate. In the complexes [RuCl2(p-cymene)L1], [cis-PtCl2(L1)2] (9), trans-[PdCl2(L1)2], [Pd(8-mq)Cl(Ln)] (8-mqH = 8-methylquinoline, n = 1–3), [Pd(dmba)Cl(L1)] (dmbaH = N,N-dimethylbenzylamine), [Pd(η3-C4H7)Cl(L2)], [Rh(acac)(CO)Ln] (n = 1–3) and [RhCl(CO)(L1)2], the phosphites behave as a monodentate phosphorus donor ligands. Owing to their steric crowding, the two cis-disposed ligands of complex 9 cannot freely rotate about their coordination axis. In the solid state, the calixarene backbones of complex 9 display a so-called ‘up-up-out-up’ conformation. Chelating phosphite behaviour was found in the cationic complexes [Pd(8-mq)Ln]BF4 (n = 1–3). In solution, the large, chelating P,O-loop of the latter complexes swings from one side of the metal plane to the other, the dynamics possibly being facilitated by the flexibility of the calixarene backbone. The four oxo-functionalised phosphites were tested as catalysts for 1-octene hydroformylation. The observed reaction rates lie in the range reported for other medium-bulky phosphites. Furthermore, the hydroformylation rate decreases as the donor strength of the side group increases, suggesting binding of the O-donor during catalysis. The L/B ratios lie in the range 1.4–3.6, the highest linear aldehyde selectivity being observed with the phosphite ester L3.

Rhodium-Catalyzed Hydroformylation and Deuterioformylation with Pyrrolyl-Based Phosphorus Amidite Ligands: Influence of Electronic Ligand Properties

The influence of electronic ligand properties on the catalyst performance in the rhodium-catalyzed hydroformylation of alkenes has been investigated. Two bidentate phosphorus amidite and phosphinite ligands have been synthesized: 1,1‘-biphenyl-2,2‘-diyl-bis(dipyrrolylphosphoramidite) (3) and 1,1‘-biphenyl-2,2‘-diyloxy-bis(diphenylphosphinite) (4). Their monodentate analogues have also been studied: phenyldipyrrolylphosphoramidite (1) and phenyl diphenylphosphinite (2). These two sets of ligands have very similar steric properties but the amidites are much stronger π-acceptor ligands. Spectroscopic studies showed that under hydroformylation reaction conditions the monodentate ligands 1 and 2 form mixtures of HRhL2(CO)2 and HRhL3(CO) complexes depending on the ligand and rhodium concentrations and the carbon monoxide pressure. Depending on the reaction conditions, the bidentate ligands 3 and 4 form mixtures of HRh(L∩L)(CO)2 and HRh(L∩L)(L∩L‘)(CO), where L∩L‘ functions as a monodentate. All ligands have been tested in the hydroformylation reaction of oct-1-ene. A high π-acidity of the ligand resulted in a high rate of hydroformylation. The monodentate ligands 1 and 2 showed moderate selectivity for the linear aldehyde. The catalyst formed with the bidentate phosphorus amidite ligand 3 revealed high regioselectivity for the linear aldehyde (ratio l/b = ∼100) at a high rate together with a moderate selectivity for isomerization (∼7%). Deuterioformylation experiments of 1-hexene showed that the hydride (deuteride) migration is reversible in the hydroformylation system formed by 3. Surprisingly, both the linear rhodium−alkyl and the branched rhodium−alkyl complex undergo β-hydride elimination. Furthermore, the 2-hexylrhodium intermediate regenerates more often monodeuterated 1-hexene than 2-hexene. The rhodium hydride species formed this way reacts relatively slowly with the excess of D2 and as a result large amounts of monodeuterated heptanal (40% D1 vs 60% D2) and monodeuterated 1-hexene are formed. At higher conversions the latter gives trisdeuterated heptanal as well as bisdeuterated heptanal.

Effect of reaction engineering factors on biphasic hydroformylation of 1-dodecene catalyzed by water-soluble rhodium complex

Hydroformylation of 1-dodecene in a biphasic system using water-soluble rhodium catalyst RhCl(CO)(TPPTS) 2 [TPPTS: tri(sodium- m-sulfonatophenyl) phosphine] was investigated. The cationic surfactant cetyltrimethyl ammonium bromide (CTAB) was used to enhance the reaction rate of long chain olefin and the ratio of normal/isomeric aldehyde. Experiments were carried out semi-batchwise in a 500 ml stirred autoclave at 100 °C and 1.1 MPa. An orthogonal experimental design was adopted for analyzing the effects of agitation intensity, 1-dodecene concentration, surfactant concentration and organic/water volume ratio on the macro-kinetics and regioselectivity. Several agitation configurations for improving the mixing, dispersion and interphase mass transfer of this gas–liquid–liquid reaction system were tested and higher hydroformylation rate and regioselectivity were achieved. The relationship between the extent of emulsification of reaction mixture and the performance of hydroformylation reaction was also studied. Empirical macro-kinetic equations for the initial rate and the correlation of normal/isomeric aldehyde ratio are proposed, which represented the experimental data reasonably well.

Influence of an Additional Gas on the Hydroformylation and Related Reactions

The initial rate of the catalytic carbonylations reported in this paper [the hydroformylation of olefins in the presence of Co2(CO)8, the carbonylation of orthoesters catalyzed by Co2(CO)8], and the formation of tetracarbonylhydridocobalt(I) from octacarbonyldicobalt and dihydrogen] was reduced by the addition of dinitrogen, argon, or xenon. The influence of xenon on the rate of hydroformylation was greater than that of dinitrogen or argon. Helium and neon, on the other hand, did not show any influence, as expected, in view of their chemical-physical features. The experimental data may be explained assuming that the additional gas competes with one or more reactants for a coordinatively unsaturated site responsible for their activation, thus affecting the reaction rate. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Positive and negative effects of Na 2SO 4 on the biphasic hydroformylation catalyzed by RhCl(CO)(TPPTS) 2–TPPTS–CTAB

Not only Na 2SO 4 has positive effect, but also negative effect on the reaction rate of biphasic hydroformylation of hexene-1 catalyzed by the complicated catalytic system – RhCl(CO)(TPPTS) 2–TPPTS–CTAB. With the suitable concentration of Na 2SO 4 added to the reaction system, the TOF would reach a maximum value. The corresponding optimal [Na 2SO 4]/[Rh] value for TOF is different with different [Rh]/[TPPTS] ratios in this catalytic system. On the contrary, no marked effect of Na 2SO 4 on the selectivity has been found in this system.

Influence of an additional gas on the hydroformylation of cyclohexene with Co 2(CO) 6(PBu 3) 2

The influence of an additional gas on the hydroformylation of cyclohexene in the presence of Co 2(CO) 6(PBu 3) 2 has been tested. The rate of the hydroformylation is reduced by the presence of an appropriate amount of dinitrogen, argon or xenon as additional gas. The conversion decreases as the pressure of the additional gas increases. Helium, on the other hand, does not show any influence. These results are in agreement with the previous data reported for the hydroformylation of the same olefin in the presence of Co 2(CO) 8 even if the entity of the reduction of the reaction rate is now less evident. The reduced influence of the additional gas may be attributed to the more severe conditions necessary to perform the reaction or to the higher stability of the catalytic system. The analogy between these two catalytic systems is confirmed by the comparable influence displaced by the additional gas. This influence on the reaction rate may be attributed, on a molecular basis, to a competition among the additional gas and dihydrogen and/or olefin to a coordinatively unsaturated place on the catalytically active complex. The formation of an additional gas containing complex reduces the concentration of the active cobalt intermediate available for the catalysis and, as a consequence, the hydroformylation rate. These data are not sufficient to identify the step of the catalytic process influenced by the presence of the additional gas, however, indicate the involvement of a dihydrogen or an olefin containing complex in the rate determining step of the hydroformylation. The formation of a cobalt complex containing an additional gas as ligand (dinitrogen, argon or xenon) in the conditions required to perform the hydroformylation is supported by these experiments.