Styrene Hydroformylation with In Situ Hydrogen: Regioselectivity Control by Coupling with the Low-Temperature Water–Gas Shift Reaction

The hydroformylation of olefins is one of the most important homogeneously catalyzed industrial reactions for aldehyde synthesis. Various ligands can be used to obtain the desired linear aldehydes in the hydroformylation of aliphatic olefins. However, in the hydroformylation of aromatic substrates, branched aldehydes are formed preferentially with common ligands. In this study, a novel approach to selectively obtain linear aldehydes in the hydroformylation of styrene and its derivatives was developed by coupling with a water–gas shift reaction on a Rh single-atom catalyst without the use of ligands. Detailed studies revealed that the hydrogen generated in situ from the water–gas shift is critical for the highly regioselective formation of linear products. The coupling of a traditional homogeneous catalytic process with a heterogeneous catalytic reaction to tune product selectivity may provide a new avenue for the heterogenization of homogenous catalytic processes.     

Styrene Hydroformylation with In Situ Hydrogen: Regioselectivity Control by Coupling with the Low‐Temperature Water–Gas Shift Reaction

The hydroformylation of olefins is one of the most important homogeneously catalyzed industrial reactions for aldehyde synthesis. Various ligands can be used to obtain the desired linear aldehydes in the hydroformylation of aliphatic olefins. However, in the hydroformylation of aromatic substrates, branched aldehydes are formed preferentially with common ligands. In this study, a novel approach to selectively obtain linear aldehydes in the hydroformylation of styrene and its derivatives was developed by coupling with a water–gas shift reaction on a Rh single‐atom catalyst without the use of ligands. Detailed studies revealed that the hydrogen generated in situ from the water–gas shift is critical for the highly regioselective formation of linear products. The coupling of a traditional homogeneous catalytic process with a heterogeneous catalytic reaction to tune product selectivity may provide a new avenue for the heterogenization of homogenous catalytic processes.     

Synthesis and characterization of poly(3-acetyl-4-hydroxyphenyl acrylate) and its Cu(II) and Ni(II) complexes

3-Acetyl-4-hydroxyphenyl acrylate (AHPA) was synthesized by treating acryloyl chloride with 2,5-dihydroxy acetophenone in the presence of triethylamine at 0 °C. AHPA was polymerized in ethyl methyl ketone (EMK) at 70 °C by free radical polymerization under nitrogen atmosphere using benzoyl peroxide as initiator. The monomer and the polymer were characterized by FT-IR, ¹H-NMR and ¹³C-NMR spectroscopy. The polymer-metal complexes were obtained by the reaction of chloroform solution of poly(AHPA) with aqueous solution of Cu(II)/Ni(II) acetates. The polymer-metal complexes were characterized by FT-IR and the results revealed that the ligands are coordinated through the oxygen of the keto group and oxygen of the phenolic -OH group to the metal ions. The electronic spectra and magnetic moment of polymer-metal complexes showed an distorted octahedral and square planar structure for poly(AHPA)-Ni(II) and poly(AHPA)-Cu(II) complexes respectively. The X-ray diffraction studies revealed that while the polymer was amorphous the polymer-metal complexes were crystalline. The thermal stability and glass transition temperature of the polymer-metal complexes were found to be higher than that of the polymer.     

Rhodium/Phosphine catalysed selective hydroformylation of biorenewable olefins

This work reports rhodium catalyzed selective hydroformylation of natural olefins like eugenol, estragole, anethole, prenol and isoprenol using biphenyl based Buchwald phosphine ligands (S‐Phos ( L ₁ ), t‐Bu XPhos ( L ₂ ), Ru‐Phos ( L ₃ ), Johnphos ( L ₄ ) and DavePhos ( L ₅ ). Ru‐Phos ( L ₃ ) ligand exhibited high impact on the hydroformylation of eugenol providing high selectivity (90%) of linear aldehyde as major product. In addition, internal natural olefins like anethole and prenol provided moderate to high selectivity (65% and 85% respectively) of branched aldehydes as a major products. The various reaction parameters such as influence of ligands, P/Rh ratio, syngas pressure, temperature, time and solvents have been studied. A high activity and selectivity gained on the way to the linear aldehydes it may be due to the bulky, steric cyclohexyl and isopropoxy groups present in L ₃ phosphine ligand. Moreover, this catalytic system was smoothly converting natural olefins into corresponding linear and branched aldehydes with higher selectivity under the mild reaction conditions.     

Highly selective hydroaminomethylation of internal alkenes to give linear amines

The application of phenoxaphosphino-modified Xantphos-type ligands (1-9) in the rhodium-catalyzed hydroaminomethylation of internal olefins to give linear amines is reported. Excellent chemo- and regioselectivities have been obtained through the use of 0.1 mol % [Rh(cod)2]BF(4)/0.4 mol % xantphenoxaphos (1), providing a practical and environmentally attractive synthetic route for the preparation of amines from internal alkenes. For the first time, both functionalized internal olefins and mixtures of internal and terminal olefins have been converted highly selectively into linear amines. Investigations of the effects of the calculated natural bite angles of ligands on hydroaminomethylation shows that the regioselectivity for the linear product follows a similar trend to that seen in the hydroformylation of internal alkenes with the aid of these ligands. Hydroaminomethylation and each of its individual steps were monitored by high-pressure infrared spectroscopy. The results suggest that hydroaminomethylations take place by a sequential isomerization/hydroformylation/amination/hydrogenation pathway.     

Modification of rhodium carbonyl catalysts for hydroformylation of 2-butenes by organophosphorus ligands

The influence of the nature of the organophosphorus ligand and the P/Rh molar ratio on the catalytic properties of rhodium carbonyl complexes in hydroformylation of 2-butenes was studied. The difference between phosphine and phosphite ligands during the formation of highly selective catalytic complexes was found. It was supposed that a decrease in the selectivity with respect to 2-methylbutanal is due to the isomerization of olefins under conditions of a decrease in the competitive capability of CO for coordination sites (the high P/Rh ratio, a decrease in the total pressure of the synthesis-gas). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 702–704, April, 1999.     

Sigma-Pi Rearrangements of Organotransition Metal Compounds

σ-Bonded organic groups in transition-metal complexes can rearrange to π-bonding ligands and vice versa: the classic example is the formation of π-arenechromium complexes from σ-arylchromium compounds. Rearrangements of this kind can be induced, inter alia, by reactions of the metal or of the ligand, as well as by migration or insertion of a ligand. Rearrangements play a role in many industrial processes, including the polymerization and isomerization of olefins and the hydroformylation of olefins.     

Synthesis and Application of Tetraphosphane Ligands in Rhodium‐Catalyzed Hydroformylation of Terminal Olefins: High Regioselectivity at High Temperature

A new class of substituted tetraphosphane ligands has been developed and applied in the rhodium‐catalyzed regioselective hydroformylation of terminal olefins. The high regioselectivity (linear selectivity is above 97 % for 1‐octene and 1‐hexene) at high temperature (140 °C) shown by these tetraphosphane ligands is remarkable considering the low regioselectivity commonly observed under similar reaction conditions when other bisphosphane analogues are used. The steric and electronic effects of substituents on the diarylphosphane moiety have also been examined.     

New tetraphosphorus ligands for highly linear selective hydroformylation of allyl and vinyl derivatives

New tetraphosphorus ligands have been developed and applied in the rhodium-catalyzed regioselective hydroformylation of a variety of functionalized allyl and vinyl derivatives. Remarkably high linear selectivity was obtained by these tetraphosphorus ligands. The ligand that bears strong electron-withdrawing 2,4-difluorophenyl groups is the most effective one in affording linear aldehydes. The Rh/tetraphosphorus ligand catalyst is highly effective to produce linear aldehydes from functionalized allyl derivatives with heteroatoms or aromatic groups directly adjacent to the allyl group. For vinyl derivatives, the ligand is highly linear selective for acrylic derivatives, styrene, vinyl pyridine, and vinyl phthalimide. Linear to branch ratios of 26:1 and 10:1 were obtained for the hydroformylation of styrene and allyl cyanide, respectively.     

Catalytic scaffolding ligands: an efficient strategy for directing reactions

The design and application of a scaffolding ligand that promotes branch and diastereoselective hydroformylation of terminal olefins as well as the regio- and diastereoselective hydroformylation of disubstituted olefins is reported. It is shown that the ligand covalently and reversibly bonds to the substrate, allowing for directed hydroformylation. As the substrate ligand interaction is dynamic, hydroformylations are catalytic in ligand and do not require any additional synthetic steps to add or remove the directing group. Using a catalytic quantity of a scaffolding ligand (20-25 mol %), excellent regioselectivity for disubstituted olefins (up to 98:2) and high branch selectivity (up to 88:12) for terminal olefins were obtained.     

HYDROFORMYLATION CATALYSIS USING POLYMER-SUPPORTED MULTINUCLEAR RHODIUM CARBONYL CLUSTER CATALYSTS

A series of polymer-supported tetranuclear rhodium carbonyl cluster catalysts were prepared b the reaction of Rh_4(CO)_(12) with several kinds of polymer supports such as crosslinked poly (N-vinylpyrrolidone) (PNVP) and crosslinked poly ( styrene-co-maleic anhydride) (PMAn), and subsequently were used to catalyze the hydroformylation of olefins. The catalysts were characterized by IR, SEM and XPS. The influence of the supports structure and crosslinking, metal's content and particle size of the supports on the catalysts hydroformylation properties was studied. The factors which affect the catalytic conversion were also examined. The experimental results show that the polymer-supported Rh cluster catalysts possess very high catalytic activity and aldehyde selectivity as well as good reproducibility.     

新型离子液体介质中长链烯烃氢甲酰化反应

合成和表征了离子液体[Rmim][p-CH3C6H4SO3](R=CH3(CH2)n—, n=3, 7, 11, 15), 并以所合成的离子液体为反应介质, 考察了水溶性铑膦络合物HRh(CO)(TPPTS)3[TPPTS: P(m-C6H4SO3Na)3]对长链烯烃氢甲酰化反应的催化性能. 结果表明, 离子液体[Rmim][p-CH3C6H4SO3]中R基团链长的变化对催化活性具有重要的影响；而在相同离子液体中, 氢甲酰化反应活性随着烯烃链长的增加明显下降. 与文献报道中广泛使用的离子液体[Bmim]BF4、[Bmim]PF6相比, 该催化体系对长链烯烃氢甲酰化反应具有更好的活性和化学选择性, 在3.0 MPa, 100 ℃的条件下, 1-己烯氢甲酰化反应转化频率(TOF)高达2736 h-1. 反应完成后, 水溶性铑膦络合物能很好地溶解在离子液体中, 与有机物自动分层, 催化剂的循环使用易于实现.     

New supramolecular transition metal catalysts

The covalent connection of a catalytically active transition metal center with a water-soluble receptor (host molecule) generates a new type of supramolecular catalyst in which the features of molecular recognition, phase transfer catalysis and transition metal catalysis are combined in a single system. The first examples of this principle make use of commercially available β-cyclodextrin (β-CD) as the receptor and rhodium complexes of diphosphanes as the catalytically active center, these being covalently connected to one another via a spacer. In competitive hydrogenation of certain olefins, unusual degrees of substrate selectivity based on molecular recognition are observed, not possible by conventional transition metal catalysts. The two-phase (water/organic) hydrogenation of nitro-aromatics also is a smooth process catalyzed by these supramolecular complexes. They also constitute an unusually active catalyst system for the selective hydroformylation of higher olefins such as 1-octene in a two-phase system. Dendrimers having diphosphane moieties on the surface provide ligands for transition metals, the corresponding metal complexes (e.g., Pd) functioning as efficient catalysts which can be recycled due to their nanoscopic properties.     

Iridium-Catalyzed Domino Hydroformylation/Hydrogenation of Olefins to Alcohols: Synergy of Two Ligands

A novel one-pot iridium-catalyzed domino hydroxymethylation of olefins, which relies on using two different ligands at the same time, is reported. DFT computation reveals different activities for the individual hydroformylation and hydrogenation steps in the presence of mono- and bidentate ligands. Whereas bidentate ligands have higher hydrogenation activity, monodentate ligands show higher hydroformylation activity. Accordingly, a catalyst system is introduced that uses dual ligands in the whole domino process. Control experiments show that the overall selectivity is kinetically controlled. Both computation and experiment explain the function of the two optimized ligands during the domino process.     

Rhodium/bisphosphite catalytic system for hydroformylation of styrene and its derivatives

Different kinds of mono‐ and bidentate phosphite ligands were used in Rh‐catalyzed hydroformylation of styrene to illustrate the influence of steric and electronic properties of ligands on catalytic performance. High activity (99.9%) and good regioselectivity (85.4%) to the linear aldehyde were achieved under optimum conditions in the presence of Rh/bisphosphite complex (bisphosphite: 2,2′‐bis(dipyrrolylphosphinooxy)‐1,1′‐(±)‐binaphthyl). This system makes it possible to prepare functionalized terminal aldehydes from readily available styrene or its derivatives through hydroformylation with high linear selectivity. Copyright © 2013 John Wiley & Sons, Ltd.     

Modular Synthesis of Phosphite and Phosphoramidite Ligands for Rh-Catalyzed Hydroformylation

Rhodium-catalyzed hydroformylation of olefins is an important method for synthesizing aldehydes, and it is worth noting that regioselectivity and enantioselectivity of the product controlled by ligand are the most commonly used strategies. The modular synthesis of phosphite and phosphoramidite ligands have significant advantages of simple synthesis and high catalytic activity, which was why these ligands have been widely used in hydroformylation reactions. Herein, we focus on the synthesis methods and design ideas of such ligands, as well as their application effects in hydroformylation reactions. This review aims to provide a reference for the design and synthesis of ligands in hydroformylation subsequently.     

Water/Oil Biphasic Hydroformylation of Higher Olefins over a TPPTS-Rh/SiO2 Catalyst

A novel TPPTS-Rh/SiO2 catalyst, prepared by directly modifying a heterogeneous highsurface-area Rh/SiO2 catalyst with water-soluble TPPTS ligands, could decrease the resistance of mass transfer in water/oil biphasic media for the hydroformylation of higher olefins. The catalytic performance for hydroformylation on this biphasic TPPTS-Rh/SiO2 catalyst system was higher than those of the traditional biphasic HRhCO(TPPTS)3 systems, owing to the chemical bonds between the highly dispersed Rh metal particles and the TPPTS ligands. The catalyst system is applicable for hydroformylation of higher olefins such as 1-dodecene.     

Water／Oil Biphasic Hydroformylation of Higher Olefins over a TPPTS-Rh／SiO2 Catalyst

A novel TPPTS-Rh/SiO2 catalyst, prepared by directly modifying a heterogeneous high-surface-area Rh/SiO2 catalyst with water-soluble TPPTS ligands, could decrease the resistance of masstransfer in water/oil biphasic media for the hydroformylation of higher olefins. The catalytic performancefor hydroformylation on this biphasic TPPTS-Rh/SiO2 catalyst system was higher than those of thetraditional biphasic HRhCO(TPPTS)3 systems, owing to the chemical bonds between the highly dispersedRh metal particles and the TPPTS ligands. The catalyst system is applicable for hydroformylation ofhigher olefins such as 1-dodecene.     

High-pressure investigations under CO/H2 of rhodium complexes containing hemispherical diphosphites

The two rhodium complexes [Rh(acac)(L(R))] (L(R)=(S,S)-5,11,17,23-tetra-tert-butyl-25,27-di(OR)-26,28-bis(1,1'-binaphthyl-2,2'-dioxyphosphanyloxy)calix[4]arene; 6: R=benzyl, 7: R=fluorenyl), each based on a hemispherical chelator forming a pocket about the metal centre upon chelation, are active in the hydroformylation of 1-octene and styrene. As expected for this family of diphosphanes, both complexes resulted in remarkably high selectivity towards the linear aldehyde in the hydroformylation of 1-octene (l/b≈15 for both complexes). Linear aldehyde selectivity was also observed when using styrene, but surprisingly only 6 displayed a marked preference for the linear product (l/b=12.4 (6) vs. 1.9 (7)). A detailed study of the structure of the complexes under CO or CO/H(2) in toluene was performed by high-pressure NMR (HP NMR) and FT-IR (HP-IR) spectroscopies. The spectroscopic data revealed that treatment of 6 with CO gave [Rh(acac)(CO)(η(1)-L(benzyl))] (8), in which the diphosphite behaves as a unidentate ligand. Subsequent addition of H(2) to the solution resulted in a well-defined chelate complex with the formula [RhH(CO)(2)(L(benzyl))] (9). Unlike 6, treatment of complex 7 with CO only led to ligand dissociation and concomitant formation of [Rh(acac)(CO)(2)], but upon addition of H(2) a chelate complex analogous to 9 was formed quantitatively. In both [RhH(CO)(2)(L(R))] complexes the diphosphite adopts the bis-equatorial coordination mode, a structural feature known to favour the formation of linear aldehydes. As revealed by variable-temperature NMR spectroscopy, these complexes show the typical fluxionality of trigonal bipyramidal [RhH(CO)(2)(diphosphane)] complexes. The lower linear selectivity of 7 versus 6 in the hydroformylation of styrene was assigned to steric effects, due to the pocket in which the catalysis takes place being less adapted to accommodate CO or larger olefins and, therefore, possibly leading to facile ligand decoordination. This interpretation was corroborated by an X-ray structure determination carried out for 7.     

Water/Oil Diphasic Hydroformylation of Higher Olefins over a TPPTS-Rh/SiO_2 Catalyst

A novel TPPTS-Rh/SiO2 catalyst, prepared by directly modifying a heterogeneous high-surface-area Rh/SiO2 catalyst with water-soluble TPPTS ligands, could decrease the resistance of mass transfer in water/oil biphasic media for the hydroformylation of higher olefins. The catalytic performance for hydroformylation on this biphasic TPPTS-Rh/SiO2 catalyst system was higher than those of the traditional biphasic HRhCO(TPPTS)3 systems, owing to the chemical bonds between the highly dispersed Rh metal particles and the TPPTS ligands. The catalyst system is applicable for hydroformylation of higher olefins such as 1-dodecene.