Evidence of colloidal rhodium formation during the biphasic hydroformylation of 1‐octene with thermoregulated phase‐transfer phosphine rhodium(I) catalyst

A thermoregulated phase‐transfer (TRPT) Rh(I) complex catalyst A prepared from Rh(acac)(CO)₂ and a thermoregulated ligand CH₃(OCH₂CH₂)_mPPh₂ (M_w = 918) was applied to the biphasic hydroformylation of 1‐octene, and a high activity with an aldehyde yield of 97.5% was demonstrated. After three recycling steps, the aldehyde yield gradually decreased. Transmission electron microscopy (TEM) revealed that after the first cycle Rh colloids were generated in situ in the aqueous phase, and in subsequent runs Ostwald ripening occurred. An independently prepared colloidal Rh(0) TRPT catalyst D also exhibited high hydroformylation activity under identical experimental conditions, and after two times of recycling an activity decrease was also observed. It is suggested that in situ from Rh(acac)(CO)₂ colloidal Rh particles are generated, which demonstrate thermomorphic behaviour and a high hydroformylation activity. Subsequently, agglomeration processes result in an activity decay, as observed in the TRPT Rh(I) complex catalyst system. Copyright © 2005 John Wiley & Sons, Ltd.     

Rhodium‐catalysed hydroformylation of 1‐octene using aryl and ferrocenyl Schiff base‐derived ligands

Monometallic and heterobimetallic complexes of Rh(I) bearing chelating N ,O ‐bidentate aryl‐ and ferrocenyl‐derived ligands have been synthesised via Schiff base condensation reactions, and characterised fully using ¹H NMR, ¹³C{¹H} NMR and Fourier transform infrared spectroscopies, elemental analysis and mass spectrometry. The new monometallic and heterobimetallic complexes were evaluated as potential catalyst precursors in the hydroformylation of 1‐octene at 95°C and 40 bar. The ferrocenylimine mononuclear compounds were inactive in the hydroformylation experiments. The Rh(I) monometallic and the ferrocene–Rh(I) heterobimetallic pre‐catalysts displayed good activity and conversion of 1‐octene as well as outstanding chemoselectivity towards aldehydes in the hydroformylation reaction.     

Xantphite: A New Family of Ligands for Catalysis. Applications in the Hydroformylation of Alkenes

The novel bulky diphosphite (P∩P) ligands ( 3 and 4 ) based on the 2,7,9,9‐tetramethyl‐9H‐xanthene‐4,5‐diol ( 2 ) backbone were investigated in the Rh‐catalyzed hydroformylation of oct‐1‐ene, styrene, and (E)‐oct‐2‐ene. These diphosphites gave rise to very active and selective catalysts for the hydroformylation of oct‐1‐ene to nonanal with average rates>10000 (mol aldehyde)(mol Rh)⁻¹h⁻¹ (P(CO/H₂)=20 bar, T=80°, [Rh]=1 mM ) and maximum selectivities of 79% for the linear product. Relatively high selectivities towards the linear aldehyde (up to 70%, linear/branched up to 2.3) but very high activities (up to 39000 (mol aldehyde)(mol Rh)⁻¹h⁻¹) were observed for the hydroformylation of styrene in the presence of these bidentate ligands (P(CO/H₂)=2 – 10 bar, T=120°, [Rh]=0.2 mM ). Remarkable activities (up to 980 (mol aldehyde)(mol Rh)⁻¹h⁻¹) were achieved with these diphosphites for the hydroformylation of (E)‐oct‐2‐ene with selectivities for the linear product of 74% (l/b up to 2.8, P(CO/H₂)=2 bar, T=120°, [Rh]=1 mM ). A detailed study of the solution structure of the catalyst under catalytic conditions was performed by NMR and high‐pressure FT‐IR. The spectroscopic data revealed that under hydroformylation conditions, the bidentate ligands rapidly formed stable, well‐defined catalysts with the structure [RhH(CO)₂(P∩P)]. All the ligands showed a preference for an equatorial‐apical ( ea ) coordination mode in the trigonal bipyramidal Rh‐complexes, indicating that a bis‐equatorial ( ee ) coordination is not a prerequisite for highly selective catalysts.     

Unusual behavior of o,o"-dimethylene(tri-p-cresyl) bicyclophosphite as a novel organophosphorus ligand in olefin hydrogenation and hydroformylation

A representative of the new class of organophosphorus ligands, viz., o,o"-dimethylene(tri-p-cresyl) bicyclophosphite (BCP), was studied as a promoter of Rh(acac)(CO)₂ in hydrogenation and hydroformylation. BCP enhances the activity and stability of the catalyst much more strongly than analogous organophosphorus ligands used previously (triphenylphosphine, triphenyl phosphite, and etriolphosphite). A reason for this behavior of BCP was studied using NMR spectroscopy, quantum-chemical calculations, and molecular simulation. The high sensitivity of the ¹H NMR signals of the methylene groups of BCP toward complexation appears due to the high density of the highest occupied and lowest unoccupied MO of protons of the CH₂ groups, especially those directed toward the P atom. The ¹H and ³¹P NMR spectra indicate the formation of hydrides of two types (HRh(BCP)₃ and HRh(BCP)₄) directly upon the addition of BCP in amounts exceeding that corresponding to the BCP/Rh = 2 ratio to a solution of Rh((acac)(CO)₂. The most probable source of the hydride ion is the BCP molecule itself, namely, the bridging CH₂ groups. The molecular mechanics simulation showed that in the [Rh(BCP)₃]⁺ complexes the aromatic rings of BCP formed two molecular cavities. These cavities can alternatively open and close, thus providing flexible screening of the catalytic site. This explains the unusual behavior of the Rh complexes with BCP in hydrogenation and hydroformylation.     

Rapid Asymmetric Transfer Hydroformylation (ATHF) of Disubstituted Alkenes Using Paraformaldehyde as a Syngas Surrogate

As an alternative to conventional asymmetric hydroformylation (AHF), asymmetric transfer hydroformylation (ATHF) by using formaldehyde as a surrogate for syngas is reported. A catalyst derived from commercially available [Rh(acac)(CO)₂] (acac=acetylacetonate) and 1,2‐bis[(2S,5S)‐2,5‐diphenylphospholano]ethane(1,5‐cyclooctadiene) (Ph‐BPE) stands out in terms of both activity and enantioselectivity. Remarkably, not only are high selectivities achievable, the reactions are very simple to perform, and higher enantioselectivity (up to 96 % ee) and/or turnover frequencies than those achievable by using the same catalyst (or other leading catalysts) can be obtained by using typical conditions for AHF.     

编织芳基网络聚合物负载Rh催化剂上高碳烯烃氢甲酰化反应性能

考察了编织芳基网络聚合物（KAPs）负载的Rh催化剂（Rh/KAPs）在高碳烯烃氢甲酰化反应中的催化性能. 结果表明,三苯基膦-苯基底KAPs负载Rh催化剂（Rh/KAPs-1）具有优异的高碳烯烃氢甲酰化反应活性,产物醛收率显著高于Rh/SiO₂催化剂. 傅里叶变换红外光谱、热重、氮气吸附-脱附、X射线衍射、透射电子显微镜、¹³C核磁共振和³¹P核磁共振结果显示,Rh/KAPs-1催化剂具有优异的热稳定性及大的比表面积和多级孔道结构,Rh颗粒处于高度分散状态,并可在反应过程中形成均相催化活性物种.     

Studies on the Synthesis of Sulfur-Containing Polymer-Rhodium Complexes and Their Use as Catalysts for Hydroformylation

A kind of nonphosphine polymer catalyst has been synthesized by partial substitution of the chlorine atoms of poly(vinyl chloride) with -SR groups (n-propyl, n-hexyl, benzyl, and p-tolyl). Rhodium complexes of these sulfur-containing polymer ligands are highly active catalysts for the hydroformylation of α-olefins. At 60°C and 60 kg/cm², conversion of 1-hexene was nearly complete within 4–6 h. The rhodium to 1-hexene mole ratio was 1/800 to 1/1 000, and the catalyst could be reused once again without losing activity. The effects of reaction temperature, pressure, H₂/CO ratio, S/Rh ratio, concentration of catalyst, and reaction time on the catalyst's activity were examined. The possible mechanism of hydroformylation is discussed. A copolymer of butyl vinyl sulfide and acrylonitrile was synthesized and its rhodium complex was prepared. The catalytic acitvities of this complex for the hydroformylation of 1-hexene was also investigated.     

Polymer-bound bulky-phosphite modified rhodium hydroformylation catalysts

Attachment of phosphites to styrene copolymers is described which are used as rhodium hydroformylation catalysts. The influence of the chain loading on the activity and complex formation of three types of copolymer-bound rhodium hydroformylation catalysts in comparison with their low molecular weight analogues has been studied. The catalytic activity of the polystyrene-bound system with the most bulky phosphite, the first system studied, is identical to that of the low molecular weight analogue. The catalysts show a high activity towards the hydroformylation of the otherwise unreactive cyclooctene. It was found that only one phosphite is coordinated to the rhodium complex in its active form. An equilibrium between this complex and an inactive complex without phosphite ligands prohibits its use in continuous flow reactors. Secondly, as polymer support a perfectly random copolymer of styrene and less bulky 3,3′,5,5′-tetra-tert-butylbiphenyl-2,2′-diyl p-vinylphenylphosphite was used. The chain loading α of this copolymer with phosphite ligands has a large influence on the complex formation of the catalyst. With high chain loadings moderately active bis-phosphite catalysts are formed. Low chain loadings give active, easily accessible, monophosphite complexes. The active species in the hydroformylation of sterically hindered alkenes is a mono-phosphite rhodium complex. The activity of the copolymer-bound catalyst towards the hydroformylation of cyclooctene is found to be as high as the activity of its low molecular weight analogue. For styrene, this polymer catalyst yields a slower catalyst than the low-molecular weight analogue. The third part demonstrates that silica-grafted polymer-bound phosphite modified rhodium complexes can be used in continuous flow reactors. The hydroformylation of styrene was carried out at moderate pressure (pCO/H₂ = 3 MPa) and temperature (T = 100°C), yielding constant conversions over a period of at least ten days. These positive results were obtained in benzene as a solvent and for a ligand to rhodium ratio of only four.     

Protic metal-containing ionic liquids as catalysts: Cooperative effects between anion and cation

HCo(CO)₄ is known to be the active species in the cobalt-catalyzed hydroformylation reaction. Although it is known that the anion [Co(CO)₄]⁻ is catalytically inactive, some cobalt carbonyl-containing ionic liquids are surprisingly able to catalyze hydroformylation reactions. However, only ionic liquids with protic cations demonstrate activity, whilst aprotic cations such as BMIM⁺ result in a completely inactive compound. The four applied cobalt-containing ionic liquids differ only by the cation component. Their different performance in catalytic activity allows the presumption of cooperative effects between the cation and the anion. These fundamental influences of the cation on the hydroformylation kinetics give hints for the reaction mechanism of biphasic hydroformylation reactions as well as on the reaction pathways of the conventional hydroformylation reaction under different reaction conditions.     

In situ formation of HRh(CO)2(PPh3)2 active species on the surface of a SBA-15 supported heterogeneous catalyst and the effect of support pore size on the hydroformylation of propene

A method of in situ formation of HRh(CO)₂(PPh₃)₂ active species on the surface of heterogeneous Rh/SBA-15 catalyst has been developed and confirmed in this work. The amount of active species formed inside the pores can be controlled by the support pore size. This class of PPh₃-Rh/SBA-15 catalyst has been employed in propene hydroformylation to be highly active, selective, stable, easily workable and recyclable. Using TEM, solid-state ³¹P MAS NMR, and in situ FT-IR, HRh(CO)₂(PPh₃)₂ active species can be characterized.     

Synthesis and reactivity of rhodium(I) complexes of the type Rh(L-L)(CO)[P(OPh)3] and Rh(L-L)[P(OPh)3]2

Summary The carbonyl ligands in the Rh¹ complexes Rh(L-L)(CO)₂ [L-L=anthranilate (AA) orN-phenylanthranilate(FA) ions] are replaced by P(OPh)₃ to form the mono-or disubstituted products, Rh(L-L)(CO)[P(OPh)₃] and Rh(L-L)[P(OPh)₃]₂ respectively depending on the [P(OPh)₃]/[Rh] molar ratio, at room temperature and in air. Under argon at [P(OPh)₃]/[Rh]4 theortho-metallated Rh¹ complex Rh[P(OPh)₃]₃[P(OC₆H₄)-OPh)₂] is formed. The new route forortho-metallated Rh¹ complex synthesis is described.The Rh(AA)(CO)₂ complex was used as a catalyst precursor in hydroformylation of olefins.     

Phosphorus Ligand Modified Rh/SiO2 Catalyst for Hydroformylation of Methyl-3-pentenoate

A phosphorus ligand-modified Rh/SiO₂ catalyst (L-Rh/SiO₂) has been developed for hydroformylation of internal olefins to linear aldehydes. This catalyst has high activity and regioselectivity and can be separated easily by filtration after reaction in an autoclave. Moreover, the electronic and steric effects of phosphorus ligands on the catalytic performance of the L-Rh/SiO₂ catalyst have been investigated by using various monodentate and chelating diphosphorus ligands.     

Spiroketal‐Based Phosphorus Ligands for Highly Regioselective Hydroformylation of Terminal and Internal Olefins

A new class of bidentate phosphoramidite ligands, based on a spiroketal backbone, has been developed for the rhodium‐catalyzed hydroformylation reactions. A range of short‐ and long‐chain olefins, were found amenable to the protocol, affording high catalytic activity and excellent regioselectivity for the linear aldehydes. Under the optimized reaction conditions, a turnover number (TON) of up to 2.3×10⁴ and linear to branched ratio (l/b) of up to 174.4 were obtained in the Rh^I‐catalyzed hydroformylation of terminal olefins. Remarkably, the catalysts were also found to be efficient in the isomerization–hydroformylation of some internal olefins, to regioselectively afford the linear aldehydes with TON values of up to 2.0×10⁴ and l/b ratios in the range of 23.4–30.6. X‐ray crystallographic analysis revealed the cis coordination of the ligand in the precatalyst [Rh( 3 d )(acac)], whereas NMR and IR studies on the catalytically active hydride complex [HRh(CO)₂( 3 d )] suggested an eq–eq coordination of the ligand in the species.     

Synthesis,characterization and hydroformylation activity of 7‐azaindolate‐bridged dinuclear rhodium(I)phosphines with pendant polar‐groups

New dinuclear Rh(I)–Phosphines of the types [Rh(µ‐azi)(CO)(L)]₂ ( 1,3 – 7 ) and [Rh(µ‐azi)(L)]₂ ( 8 ) with pendant polar groups, and a chealated mononuclear compound [Rh(azi‐H)(CO)(L)] ( 2 ) (where azi = 7‐azaindolate, L = polar phosphine) were isolated from the reaction of [Rh(µ‐Cl)(CO)₂]₂ with 7‐azaindolate followed by some polar mono‐ and bis‐phosphines ( L ₁ – L ₈ ). A relationship between Δδ³¹P‐NMR and ν(CO) values was considered to define the impact of polar‐groups on σ‐donor properties of the phosphines. These compounds were evaluated as catalyst precursors in the hydroformylation of 1‐hexene and 1‐dodecene both in mono‐ and biphasic aqueous organic systems. While the biphasic hydroformylations (water + toluene) gave exclusively the aldehydes, the monophasic one (aqueous ethanol) showed propensity to form both aldehydes and alcohols. The influence of bimetallic cooperative effects, and σ‐donor and hydrophilic properties of the phosphines with pendant polar‐groups in enhancing the yields and selectivity of hydroformylation products was emphasized. In addition, when strong σ‐donor phosphine was used, the π‐acceptor nature of pyridine ring of 7‐azaindolate spacer was found to be a considerable factor in facilitating the facile cleavage of CO group during hydroformylation and in supplementing the cooperative effects. Copyright © 2009 John Wiley & Sons, Ltd.     

Hydroformylation of Olefins Catalyzed by Rhodium Trichloride Anchored on Ti-HMS

Rhodium trichloride supported on Ti-hexagonal mesoporous silica (Ti-HMS), via a bipyridyl group, is an efficient catalyst for the hydroformylation of olefins at 120 °C and 40.8 atm of CO/H₂ (CO/H₂=2/1). The catalyst is selective leading to high ratios of linear or branched aldehydes from functionalized olefins, and high activity in the case of propene which gave a turnover frequency of 6209 mol/mol(Rh)/h.     

Sulfur Poisoning and Self-Recovery of Single-Site Rh1/Porous Organic Polymer Catalysts for Olefin Hydroformylation

Sulfur poisoning and regeneration are global challenges for metal catalysts even at the ppm level. The sulfur poisoning of single-metal-site catalysts and their regeneration is worthy of further study. Herein, sulfur poisoning and self-recovery are first presented on an industrialized single-Rh-site catalyst (Rh₁/POPs). A decreased turnover frequency of Rh₁/POPs from 4317 h⁻¹ to 318 h⁻¹ was observed in a 1000 ppm H₂S co-feed for ethylene hydroformylation, but it self-recovered to 4527 h⁻¹ after withdrawal of H₂S, whereas the rhodium nanoparticles demonstrated poor activity and self-recovery ability. H₂S reduced the charge density of the single Rh atom and lowered its Gibbs free energy with the formation of inactive (SH)Rh(CO)(PPh₃-frame)₂, which could be regenerated to active HRh(CO)(PPh₃-frame)₂ after withdrawing H₂S. The mechanism and the sulfur-related structure–activity relationship were highlighted. This work provides an understanding of heterogeneous ethylene hydroformylation and sulfur-poisoned regeneration in the science of single-atom catalysts.     

Organic Ligand‐Free Hydroformylation with Rh Particles as Catalyst†

Summary of main observation and conclusion An efficient and organic ligand-free heterogeneous catalytic system for hydroformylation of olefins is highly desirable for both academy and industry.In this study,simple Rh black was employed as a heterogeneous catalyst for hydroformylation of olefins in the absence of organic ligand.The Rh black catalyst showed good catalytic activity for a broad substrate scope including the aliphatic and aromatic olefins,affording the desired aldehydes in good yields.Taking the hydroformylation of ethylene as an example,86%yield of propanal and TOF of 200 h-1 were obtained,which was superior to the reported homogeneous catalytic systems.In addition,the catalyst could be reused five times without loss of activity under identical reaction conditions,and the Rh leaching was negligible after each cycle.     

A new air‐stable and reusable tetraphosphine ligand for rhodium‐catalyzed hydroformylation of terminal olefins at low temperature

Tetraphosphine and bisphosphine ligands were synthesized, characterized and employed in Rh‐catalyzed hydroformylation of 1‐octene and 1‐hexene. Conversion of over 97.7% and aldehyde yield of 94.1% were achieved at 60°C, 20 bar. This remarkable performance could also be retained at lower temperature (i.e. 40°C) by prolonging the reaction time. The tetraphosphine ligand‐modified Rh catalyst could be reused for at least seven successive runs with catalytic activity and selectivity almost unchanged; the catalyst was separated from the products and recycled directly in homogeneous hydroformylation, indicating that the catalyst might have good stability. ³¹P NMR and high‐resolution mass spectral characterization hinted that the reason for the reusability of the catalyst might be that the tetraphosphine ligand is relatively air‐stable and is probably slowly oxidized during the recycling runs. The tetraphosphine ligand has four phosphorus atoms to be partially oxidized and could still coordinate with the Rh center via the unoxidized phosphorus atoms to stabilize the catalyst, based on the multiple chelating modes of the tetraphosphine ligand. Hence, the catalytic activity and selectivity could be retained for a certain number of runs.     

Isolated Single Iron Atoms Anchored on N-Doped Porous Carbon as an Efficient Electrocatalyst for the Oxygen Reduction Reaction

The development of low-cost, efficient, and stable electrocatalysts for the oxygen reduction reaction (ORR) is desirable but remains a great challenge. Herein, we made a highly reactive and stable isolated single-atom Fe/N-doped porous carbon (ISA Fe/CN) catalyst with Fe loading up to 2.16 wt %. The catalyst showed excellent ORR performance with a half-wave potential (E_1/2) of 0.900 V, which outperformed commercial Pt/C and most non-precious-metal catalysts reported to date. Besides exceptionally high kinetic current density (J_k) of 37.83 mV cm⁻² at 0.85 V, it also had a good methanol tolerance and outstanding stability. Experiments demonstrated that maintaining the Fe as isolated atoms and incorporating nitrogen was essential to deliver the high performance. First principle calculations further attributed the high reactivity to the high efficiency of the single Fe atoms in transporting electrons to the adsorbed OH species.