Design and Synthesis of Isocyanide Ligands for Catalysis: Application to Rh‐Catalyzed Hydrosilylation of Ketones

New isocyanide ligands with meta‐terphenyl backbones were synthesized. 2,6‐Bis[3,5‐bis(trimethylsilyl)phenyl]‐4‐methylphenyl isocyanide exhibited the highest rate acceleration in rhodium‐catalyzed hydrosilylation among other isocyanide and phosphine ligands tested in this study. ¹H NMR spectroscopic studies on the coordination behavior of the new ligands to [Rh(cod)₂]BF₄ indicated that 2,6‐bis[3,5‐bis(trimethylsilyl)phenyl]‐4‐methylphenyl isocyanide exclusively forms the biscoordinated rhodium–isocyanide complex, whereas less sterically demanding isocyanide ligands predominantly form tetracoordinated rhodium–isocyanide complexes. FTIR and ¹³C NMR spectroscopic studies on the hydrosilylation reaction mixture with the rhodium–isocyanide catalyst showed that the major catalytic species responsible for the hydrosilylation activity is the Rh complex coordinated with the isocyanide ligand. DFT calculations of model compounds revealed the higher affinity of isocyanides for rhodium relative to phosphines. The combined effect of high ligand affinity for the rhodium atom and the bulkiness of the ligand, which facilitates the formation of a catalytically active, monoisocyanide–rhodium species, is proposed to account for the catalytic efficiency of the rhodium–bulky isocyanide system in hydrosilylation.     

Hydrosilylation reactions catalyzed by rhodium complexes with phosphine ligands functionalized with imidazolium salts

Hydrosilylation reactions of styrene with triethoxysilane catalyzed by rhodium complexes with phosphine ligands functionalized with imidazolium salts are reported. In comparison with Wilkinson’s catalyst, Rh(PPh₃)₃Cl, all of the present rhodium complexes with phosphines functionalized with imidazolium salts exhibit higher catalytic activity and selectivity.     

Synthesis and incorporation of 4-triethoxysilyl-1,2-bis(diphenylphosphino)benzene into silica gel and solgel polymers: Preparation and utilization of recyclable catalysts for alkene hydroformylation and methanol homologation

A chelating phosphine monomer, 4-triethoxysilyl-1,2-bis(diphenylphosphino)benzene ( 9 ), was prepared in three steps from 2,4-dibromoiodobenzene. Attachment of 9 to the surface of commercial silica gel, followed by chelation of rhodium, gave a catalyst which showed both undiminished activity (turnover rates of 90 atom^?1 h^?1) and no loss of rhodium over five recycles in the hydroformylation of styrene. Complexation of cobalt afforded a catalyst for the homologation of methanol. Monomer 9 could be incorporated into a solgel polymer produced from silicic acid in tetrahydrofuran, but low rhodium uptake and low catalytic activity suggested that few phosphine sites were available to the rhodium. The catalytically-active species were modeled by the synthesis of cobalt and rhodium complexes containing 1,2-bis(diphenylphosphino)benzene.     

Catalytic olefin hydrogenation with the application of a new water soluble rhodium catalyst

The catalyst precursor preparedin situ from rhodium dimer [Rh(cod)Cl]₂ and a new water-soluble phosphine Ph₂PCH₂CH₂CONHC(CH₃)₂CH₂SO₃H (in Li⁺ salt form) has been found to act as an effective olefin hydrogenation catalyst. Catalytic hydrogenation reactions have been tested in either two phase: aqueous catalyst/insoluble olefin or methanolic catalyst/olefin systems. The observed reaction rates were higher for terminal than for internal olefins. 1-Hexene in methanolic solution has been hydrogenated with a turnover frequency of about 8000 h^–1. This system has also been applied in the form of a supported aqueous phase catalyst.     

Synthesis of novel poly(ethylene glycol)‐containing imidazolium‐functionalized phosphine ligands and their application in the hydrosilylation of olefins

A series of polyethylene glycol‐containing imidazolium‐functionalized phosphine ligands (mPEG‐im‐PPh₂) were successfully synthesized and used in the rhodium‐catalyzed hydrosilylation of olefins. The results indicate that the RhCl₃/mPEG‐im‐PPh₂ catalytic system exhibits both excellent activity and selectivity for the β‐adduct. In addition, the catalytic system may be recycled at least six times.     

Regulation of Catalytic Activity by Phosphine Ligand Design

Abstract

Starting with the catalytic complex [Rh(PPh₃)₃Cl], the influence of variation of phosphine ligand properties on the activity of rhodium phosphine complexes as catalysts for the hydrogenation of olefins was systematically studied. The following catalyst modifications were examined (a) varying the basicity of the triarylphosphine ligands, (b) replacing Cl^? by a non-coordinating anion (BF₄ ^?) to make the catalyst cationic, (c) substituting a chelating diphosphine for the monophosphine ligands to ensure cis-coordination, and (d) varying the chain length of the diphosphine ligand to vary the chelate ring size and flexibility. By systematic manipulation of these parameters, enhancements of catalytic activity by factors in excess of 10⁴ were achieved.     

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[SiW₁₁O₃₉Rh] (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.     

MCM‐41‐Supported Bidentate Phosphine Rhodium Complex: An Efficient and Recyclable Heterogeneous Catalyst for the Hydrosilylation of Olefins

MCM‐41‐supported bidentate phosphine rhodium complex (MCM‐41‐2P‐RhCl₃) was conveniently synthesized from commercially available and cheapγ‐aminopropyltriethoxysilane via immobilization on MCM‐41, followed by reacting with diphenylphosphinomethanol and rhodium chloride. It was found that the title complex is a highly efficient catalyst for the hydrosilylation of olefins with triethoxysilane and can be recovered and recycled by a simple filtration of the reaction solution and used for at least 10 consecutive trials without any decreases in activity.     

Evaluation of ruthenium‐based catalytic systems for the controlled atom transfer radical polymerisation of vinyl monomers

Only [RuCl₂(p‐cymene)(PR₃)] complexes where the phosphine ligand, PR₃, is both strongly basic and bulky proved to be effective catalysts for the controlled atom transfer radical polymerisation (ATRP) of methyl methacrylate and styrene. The best phosphine ligands were typically P(i‐Pr)₃, P(cyclohexyl)₂Ph, P(cyclohexyl)₃, and P(cyclopentyl)₃. Less basic and/or bulky phosphines led to ineffective systems for ATRP. Tricyclohexylarsine gave rise to a highly efficient catalyst system. However, related complexes in which the phosphine ligand was replaced by tricyclohexylstibine, nitrogen (piperidine and 4‐cyanopyridine) and carbon ligands (alkyl isocyanides) proved to be inefficient. The observation of a direct relationship between the p‐cymene lability (measured by TGA) and catalyst activity suggests that p‐cymene release is a prerequisite for the polymerisation process.     

Rh-TPPTS/CTAB-MMT催化剂的制备及其催化长链烯烃氢甲酰化反应性能研究

通过浸渍法将水溶性铑膦配合物(Rh-TPPTS)负载到由十六烷基三甲基溴化铵(CTAB)修饰的蒙脱土(MMT)上,制备出Rh-TPPTS/CTAB-MMT负载型催化剂.采用XRD,FTIR,TG,BET,31P CP-MAS NMR和分散性实验对催化剂进行了表征.结果表明:水溶性铑膦配合物成功地负载到有机MMT上,并且该催化剂在有机溶剂中具有很好的分散性.该催化剂对于1-癸烯的氢甲酰化反应具有好的催化活性.在100℃、4 MPa、甲苯为溶剂的条件下,催化1-癸烯氢甲酰化可获得93.0%的转化率,95.8%的醛的选择性,2.1的正异比,137 h-1的TOF值.并对不同链长烯烃底物进行了考察.随着烯烃碳链的增加,醛的选择性下降,但是正异比有所增加.     

Probing the steric limits of rhodium catalyzed hydrophosphinylation. P-H addition vs. dimerization/oligomerization/polymerization

The reactivity of secondary phosphine oxides containing bulky organic fragments in hydrophosphinylation reactions has been investigated using several rhodium based catalysts. Upon heating in a focused microwave reactor, HP(O)(2-C₆H₄Me)₂ adds to prototypical terminal alkynes affording a complex mixture containing 1,2 and 1,1-addition products. Addition of a second ortho-substituent (HP(O)Mes₂) completely suppresses the hydrophosphinylation reaction for alkyl and aryl substituted alkynes. Variations in the temperature, catalyst loading, solvent, and microwave power were unable to induce an addition reaction in the case of HP(O)Mes₂. While this secondary phosphine oxide did not participate in the hydrophosphinylation reaction, it promoted the polymerization of phenylacetylene. HP(O)R₂ substrates are not commonly thought of as innocent ligands for rhodium complexes in reactions involving alkynes due to facile hydrophosphinylation. While this is certainly true for diphenylphosphine oxide, the chemistry presented herein suggests that HP(O)Mes₂ and related bulky secondary phosphine oxides have great potential as valuable ligands for rhodium catalyzed transformations involving alkynes due to their lack of reactivity towards the addition reaction.     

Markovnikov hydroformylation catalyzed by ROPAC in the presence of phosphine and phosphine oxide ligands

Rhodium-catalyzed hydroformylation of 1-octene in the presence of different phosphine and phosphine oxide ligands has been investigated. The molecular structure of new phosphine ligand, fluorenylidine methyl phenyl diphenylphosphine, was determined by single-crystal X-ray crystallography. Parameters such as different ligands, molar ratio of ligand to rhodium complex, ratio of olefin to rhodium complex, pressure of CO : H₂ mixture, and time of the reaction were studied. The linear aldehyde was the main product when the phosphine ligands were used as auxiliary ligands while the selectivity was changed to the branched products when the related phosphine oxide ligands were used. Under optimized reaction conditions, in the presence of [Rh(acac)(CO)(Ph₃P)]-di(1-naphthyl)phenyl phosphine oxide, conversion of 1-octene reached 97% with 87% selectivity of branched aldehyde.     

Influence of the ligand structure on SLP-catalysed hydroformylation of propene

Hydroformylation of propene was studied at 90–120°C and 3–10 atm. The catalyst was hydrido-(carbonyl)tris(triphenylphosphine)rhodium [H(CO)Rh(PPh₃)₃] supported on silica, in an excess of a liquid phosphine (P) ligand as solvent. The following series of ligands (P) was synthesized and studied in this application: CH₃(CH₂)_nPPh₂ (n = 3, 7, 17), (c – C₆H₁₁)_xPPh_3?x (x = 0, 1, 2) and also unsaturated allyl- and poly(butadienyl)-diphenylphosphines. The activity and regioselectivity of the catalysts are discussed in terms of the mobility and coordination ability of the ligands used. With the same electron density of the phosphorus atom, the activity of the catalysts increases with the mobility of the ligands. On the other hand, given the same mobility of the ligand, a lower electron density on phosphorus results in increased catalytic activity.     

Catalytic activity of 1‐methylimidazole‐based phosphine ligands in the palladium‐catalyzed Suzuki coupling reaction

The catalytic activities of three N‐methylimidazole‐based phosphine ligands in the Suzuki coupling reaction were tested using PdCl₂ as the catalyst. The results showed all three phosphine ligands exhibited excellent activity towards the Suzuki reaction, and the catalytic activity decreased with increasing number of imidazole groups. Copyright © 2014 John Wiley & Sons, Ltd.     

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.     

Phosphorus Ligands with a Large Cavity: Synthesis of Triethynylphosphines with Bulky End Caps and Application to the Rhodium‐Catalyzed Hydrosilylation of Ketones

Trialkynylphosphines substituted with bulky triarylsilyl groups at the alkyne termini were synthesized. The new phosphines P(C?CSiAr₃)₃ (Ar=3,5‐tBu₂‐4‐MeOC₆H₂, 3,5‐(Me₃Si)₂C₆H₃) are uncrowded near the phosphorus atom but bulky in the distal region. As a result, they contain a large cavity, at the bottom of which the phosphine lone‐pair electrons are located. The compounds are stable to oxidation by air and hydrolysis. DFT calculations suggested that the triethynylphosphines are good π‐acceptor ligands, comparable with P(OAr)₃. The trialkynylphosphines reacted with [{RhCl(cod)}₂] (P/Rh=1.1:1) to give selectively the monophosphine–rhodium complex [RhCl(cod)P(C?CSiAr₃)₃]. X‐ray crystal‐structure analysis revealed that the {RhCl(cod)} fragment is fully accommodated by the cavity of the phosphine ligand. Compared to the effect of analogues with smaller end caps and PPh₃, the trialkynylphosphines accelerated markedly the rhodium‐catalyzed hydrosilylation of ketones with a triorganosilane. It is proposed that the higher catalytic activity observed with the holey phosphines is a result of the preferential formation of a monophosphine–rhodium species.     

Catalysis of hydrosilylation XIII. Gas-phase hydrosilylation of acetylene by trichlorosilane on functionalised silica supported rhodium and ruthenium phosphine complexes

Gas-phase hydrosilylation of acetylene by tri-chlorosilane catalyzed in a continuous flow apparatus by rhodium and ruthenium phosphine complexes immobilized on the silica via mercapto, phosphine, amine and nitrile ligands has been studied. GLC analysis of the reaction products showed vinyltrichlorosilane to be accompanied by products of double hydrosilylation of acetylene and the redistribution of trichlorosilane followed by the hydrosilylation and hydrogenative hydrosilylation of acetylene with dichlorosilane. A scheme for this complex competitive–consecutive reaction was proposed. The yield and selectivity of vinyltrichlorosilane can be much improved under special reaction conditions, e.g. rate flow of the particular substrates, temperature, given catalyst and others. Kinetic measurements carried out in the range of 115–140°C allowed us to evaluate the activation energy, E_a, for the vinyltrichlorosilane synthesis, which varied between 20.5 and 27.6 kJ mol^?1 for the selected rhodium and ruthenium supported complexes.     

Development of an Improved Rhodium Catalyst for Z‐Selective Anti‐Markovnikov Addition of Carboxylic Acids to Terminal Alkynes

To develop more active catalysts for the rhodium‐catalyzed addition of carboxylic acids to terminal alkynes furnishing anti‐Markovnikov Z enol esters, a thorough study of the rhodium complexes involved was performed. A number of rhodium complexes were characterized by NMR, ESI‐MS, and X‐ray analysis and applied as catalysts for the title reaction. The systematic investigations revealed that the presence of chloride ions decreased the catalyst activity. Conversely, generating and applying a mixture of two rhodium species, namely, [Rh(DPPMP)₂][H(benzoate)₂] (DPPMP=diphenylphosphinomethylpyridine) and [{Rh(COD)(μ₂‐benzoate)}₂], provided a significantly more active catalyst. Furthermore, the addition of a catalytic amount of base (Cs₂CO₃) had an additional accelerating effect. This higher catalyst activity allowed the reaction time to be reduced from 16 to 1–4 h while maintaining high selectivity. Studies on the substrate scope revealed that the new catalysts have greater functional‐group compatibility.     

The Effect of Metal‐Ligand Affinity on Fe3O4_Supported Co–Rh Catalysts for Dicyclopentadiene Hydroformylation

The catalytic performances of Co‐Rh/Fe₃O₄ catalysts modified with phosphine ligands (PPh₃) and its analogues on dicyclopentadiene hydroformylation were evaluated. Among these catalysts, Co‐Rh/Fe₃O₄ modified with tris(p‐trifluoromethylphenyl)phosphine was determined to be effective for monoformyltricyclodecanes production, whereas Co‐Rh/Fe₃O₄ modified with PPh₃ or tri‐p‐tolylphosphine was effective for the diformyltricyclodecanes production. To investigate the ligand effects, the complex catalyst system (Co‐Rh/Fe₃O₄ and phosphine ligand) was subjected to pretreatment with syngas and then characterized by thermogravimetry and differential thermal analysis (TG‐DTA). It was determined that the threshold decomposition temperature reflected the corresponding Rh‐phosphine interaction strength, affecting the catalytic selectivity toward different products. A weak Rh‐phosphine interaction was desirable to produce monoformyltricyclodecanes with fast reaction kinetics, whereas a strong Rh‐phosphine complex was required for the synthesis of diformyltricyclodecanes. In addition to the selectivity rule shown in the PPh₃ series, experiments with other ligands also demonstrated similar selectivity trends.     

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.