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.     

One‐Pot Cooperation of Single‐Atom Rh and Ru Solid Catalysts for a Selective Tandem Olefin Isomerization‐Hydrosilylation Process

Realizing the full potential of oxide‐supported single‐atom metal catalysts (SACs) is key to successfully bridge the gap between the fields of homogeneous and heterogeneous catalysis. Here we show that the one‐pot combination of Ru₁/CeO₂ and Rh₁/CeO₂ SACs enables a highly selective olefin isomerization‐hydrosilylation tandem process, hitherto restricted to molecular catalysts in solution. Individually, monoatomic Ru and Rh sites show a remarkable reaction specificity for olefin double‐bond migration and anti‐Markovnikov α‐olefin hydrosilylation, respectively. First‐principles DFT calculations ascribe such selectivity to differences in the binding strength of the olefin substrate to the monoatomic metal centers. The single‐pot cooperation of the two SACs allows the production of terminal organosilane compounds with high regio‐selectivity (>95 %) even from industrially‐relevant complex mixtures of terminal and internal olefins, alongside a straightforward catalyst recycling and reuse. These results demonstrate the significance of oxide‐supported single‐atom metal catalysts in tandem catalytic reactions, which are central for the intensification of chemical processes.     

New highly active and selective Et oligomerization catalysts based on cationic diamide zirconium complexes

Group 4 complexes based on the diamide ligand, [Me₃CN(SiMe₂)₂NCMe₃]²⁻, have been investigated as possible catalysts for olefin conversions. The dialkyl complexes, (Me₂SiNCMe₃)₂ZrR₂ (R = CH₂Ph, Me), were converted into zwitterionic (X‐ray: {Me₂SiNCMe₃}₂Zr(η¹‐Bz){ηⁿ‐BzB(C₆F₅)₃}), or cationic mono‐alkyl compounds by reaction with B(C₆F₅)₃ or borate reagents. These electrophilic species catalyzed ethylene oligomerization, affording highly linear alpha‐olefins under mild conditions (C₆ fraction > 99.5% 1‐hexene at 50°C, 6 bar). The highest activities (290 Kg/g Zr.h) were obtained in toluene solvent using tri‐iso‐butylaluminium (TIBA) as scavenger. The catalyst exhibited activity decay in alkane solvent, which was countered by replacement of TIBA by more crowded trialkylaluminium scavengers or branched alkylaluminoxane scavengers. The product consisted primarily of linear alpha‐olefins (LAO) with low levels of remote‐branched AO's. These are formed by successive insertion of higher olefin and one or more ethylenes in a growing chain, followed by chain transfer.     

Aromatic‐Amide‐Derived Olefins as a Springboard: Isomerization‐Initiated Palladium‐Catalyzed Hydrogenation of Olefins and Reductive Decarbonylation of Acyl Chlorides with Hydrosilane

A highly efficient catalytic protocol for the isomerization of substituted amide‐derived olefins is presented that successfully uses a hydride palladium catalyst system generated from [PdCl₂(PPh₃)₂] and HSi(OEt)₃. The Z to E isomerization was carried out smoothly and resulted in geometrically pure substituted olefins. Apart from the cis–trans isomerization of double bonds, the selective reduction of terminal olefins and activated alkenes was performed with excellent functional group tolerance in the presence of an amide‐derived olefin ligand, and the products were obtained in high isolated yields (up to >99 %). Furthermore, the palladium/hydrosilane system was able to promote the reductive decarbonylation of benzoyl chloride when a (Z)‐olefin with an aromatic amide moiety was used as a ligand.     

Synthesis of glycosylated porphyrins as neutral ionophores for a berberine-sensitive electrode

For preparing a berberine-sensitive electrode, 5,10,15,20-tetrakis[2-(2,3,4,6-tetraacetyl-β-D-glucopyranosyl)-1-O-phenyl]porphyrin (T(o-glu)PPH₂) was synthesized from the reaction of pyrrole with ortho-acetylglycosylated benzaldehyde by Lindsay’s method. The electrode based on T(o-glu)PPH₂ with an optimized membrane composition exhibits Nernstian response to berberine in the concentration range 2.4 × 10^–7–5.0 × 10^–3 mol L^–1, with a pH range from 3.9 to 10.2, and a fast response time of 30 s. The electrode shows fair selectivity towards berberine with respect to common co-existing species. T(o-glu)PPH₂ shows better potentiometric response characteristics comparing to chloro[5,10,15,20-tetrakis[2-(2,3,4,6-tetraacetyl-β-D-glucopyranosyl)-1-O-phenyl]-porphinato]-manganese (MnT(o-glu)PPCl) and better selectivity towards berberine than tetraphenylporphyrin (TPPH₂). The effect of the composition of the electrode membrane has been studied and the experimental conditions optimized. The contents of berberine in pharmaceutical tablets were determined by direct potentiometry and the results agreed with values obtained by the pharmacopoeia method. Received: 17 July 2000 / Revised: 18 September 2000 / Accepted: 23 October 2000     

Mild olefin formation via bio-inspired vitamin B12 photocatalysis

Dehydrohalogenation, or elimination of hydrogen-halide equivalents, remains one of the simplest methods for the installation of the biologically-important olefin functionality. However, this transformation often requires harsh, strongly-basic conditions, rare noble metals, or both, limiting its applicability in the synthesis of complex molecules. Nature has pursued a complementary approach in the novel vitamin B₁₂-dependent photoreceptor CarH, where photolysis of a cobalt–carbon bond leads to selective olefin formation under mild, physiologically-relevant conditions. Herein we report a light-driven B₁₂-based catalytic system that leverages this reactivity to convert alkyl electrophiles to olefins under incredibly mild conditions using only earth abundant elements. Further, this process exhibits a high level of regioselectivity, producing terminal olefins in moderate to excellent yield and exceptional selectivity. Finally, we are able to access a hitherto-unknown transformation, remote elimination, using two cobalt catalysts in tandem to produce subterminal olefins with excellent regioselectivity. Together, we show vitamin B₁₂ to be a powerful platform for developing mild olefin-forming reactions.

Terminal or subterminal olefins can be selectively formed from alkyl electrophiles via bio-inspired vitamin B₁₂ photocatalysis.     

Direct and Highly Selective Conversion of Synthesis Gas into Lower Olefins: Design of a Bifunctional Catalyst Combining Methanol Synthesis and Carbon–Carbon Coupling

The direct synthesis of lower (C₂ to C₄) olefins, key building‐block chemicals, from syngas (H₂ /CO), which can be derived from various nonpetroleum carbon resources, is highly attractive, but the selectivity for lower olefins is low because of the limitation of the Anderson–Schulz–Flory distribution. We report that the coupling of methanol‐synthesis and methanol‐to‐olefins reactions with a bifunctional catalyst can realize the direct conversion of syngas to lower olefins with exceptionally high selectivity. We demonstrate that the choice of two active components and the integration manner of the components are crucial to lower olefin selectivity. The combination of a Zr–Zn binary oxide, which alone shows higher selectivity for methanol and dimethyl ether even at 673 K, and SAPO‐34 with decreased acidity offers around 70 % selectivity for C₂–C₄ olefins at about 10 % CO conversion. The micro‐ to nanoscale proximity of the components favors the lower olefin selectivity.     

Libraries via Metathesis of Internal Olefins

The cross-metathesis of internal olefins is applied for the combinatorial synthesis of small organic molecules; this reaction is conveniently carried out in neat olefin (oleic-acid derivatives) and requires only 0.001 equiv. of [Ru(CHPh)Cl₂(PCy₃)₂] as catalyst (Cy = cyclohexyl).     

Calcium‐Based Lewis Acid Catalysts

Recently, Lewis acidic calcium salts bearing weakly coordinating anions such as Ca(NTf₂)₂, Ca(OTf)₂, CaF₂ and Ca[OCH(CF₃)₂]₂ have been discovered as catalysts for the transformation of alcohols, olefins and carbonyl compounds. High stability towards air and moisture, selectivity and high reactivity under mild reaction conditions render these catalysts a sustainable and mild alternative to transition metals, rare‐earth metals or strong Brønsted acids.     

Synthesis of Citronellal by RhI‐Catalysed Asymmetric Isomerization of N,N‐Diethyl‐Substituted Geranyl‐ and Nerylamines or Geraniol and Nerol in the Presence of Chiral Diphosphino Ligands,under Homogeneous and Supported Conditions

For the asymmetric isomerization of geranyl‐ or neryldiethylamine ((E)‐ or (Z)‐ 1 , resp.) and allyl alcohols geraniol or nerol ((E)‐ or (Z)‐ 2 , resp.) to citronellal ( 4 ) in the presence of a [Rh^I(ligand)cycloocta‐1,5‐diene)]⁺ catalyst, the atropic ligands 5 – 11 are compared under homogeneous and polymer‐supported conditions with the non‐C₂‐symmetrical diphosphino ferrocene ligands 12 – 16 . The ^tBu‐josiphos ligand 13 or daniphos ligand 19 , available in both antipodal series, already catalyse the reaction of (E)‐ 1 at 20° (97% e.e.) and favourably compare with the binap ligand 5 (see Table 1). Silica‐gel‐ or polymer‐supported diphosphino ligands usually afford similar selectivity as compared to the corresponding ligands applied under homogeneous conditions, but are generally less reactive. In this context, a polymer‐supported ligand of interest is the polymer‐anchored binap (R)‐ 6 , in terms of reactivity, selectivity, and recoverability, with a turnover of more than 14400.     

Alumina-supported iron catalyst - long-term study of the light product distribution in Fischer-Tropsch synthesis

Several models have been proposed to describe the carbon number product distribution and mechanism in Fischer-Tropsch synthesis (FTS). However, these models have not fully explained the product distribution and mechanism owing to the wide range and complexity of hydrocarbons in FTS. This study was conducted based on the Yao and Anderson-Schulz-Flory (ASF) carbon number product distribution models for light (C₁–C₆) hydrocarbon products of a Fe/Al₂O₃ catalyst. The product distribution based on the molar ratio of olefin to paraffin (O/P) and the neighboring olefins was also studied in order to better understand the mechanism in FTS and C₂ olefin deviation during FTS.Two sets of experiments (A and B) with different reaction conditions were conducted in microtubular fixed-bed reactors on the Fe/Al₂O₃ catalyst for 2249 h and 360 h, respectively. We found that the α values from the Yao and ASF carbon number product distribution models are relatively similar. The α values from the Yao carbon number product distribution plots are relatively constant, irrespective of the reaction conditions.Interestingly, it was also found that the secondary reactions of the C₂ olefin by re-adsorption to produce paraffins and long-chain olefins are dependent on the CO conversion and the reaction temperature during the FTS. Also, the product distribution of the neighboring olefins during the reduction condition gave a similar trend to what was observed for other reaction conditions. This result confirmed what was observed in the Yao and ASF carbon number product distribution of the olefins.     

Development of a General and Efficient Iron‐Catalyzed Epoxidation with Hydrogen Peroxide as Oxidant

The development of inexpensive and practical iron catalysts for the environmentally benign epoxidation of olefins with hydrogen peroxide as terminal oxidant is described. By systematic variation of ligands, metal sources, and reaction conditions, it was discovered that FeCl₃?6H₂O in combination with pyridine‐2,6‐dicarboxylic acid and different amines shows high reactivity and excellent selectivity towards the epoxidation of aromatic olefins and moderate reactivity towards that of aliphatic olefins.     

One-Pot Cooperation of Single-Atom Rh and Ru Solid Catalysts for a Selective Tandem Olefin Isomerization-Hydrosilylation Process

Realizing the full potential of oxide-supported single-atom metal catalysts (SACs) is key to successfully bridge the gap between the fields of homogeneous and heterogeneous catalysis. Here we show that the one-pot combination of Ru₁/CeO₂ and Rh₁/CeO₂ SACs enables a highly selective olefin isomerization-hydrosilylation tandem process, hitherto restricted to molecular catalysts in solution. Individually, monoatomic Ru and Rh sites show a remarkable reaction specificity for olefin double-bond migration and anti-Markovnikov α-olefin hydrosilylation, respectively. First-principles DFT calculations ascribe such selectivity to differences in the binding strength of the olefin substrate to the monoatomic metal centers. The single-pot cooperation of the two SACs allows the production of terminal organosilane compounds with high regio-selectivity (>95 %) even from industrially-relevant complex mixtures of terminal and internal olefins, alongside a straightforward catalyst recycling and reuse. These results demonstrate the significance of oxide-supported single-atom metal catalysts in tandem catalytic reactions, which are central for the intensification of chemical processes.     

Transition metal-catalyzed olefin arylation via C–H bond activation of arenes

In this article, two kinds of our transition metal-catalyzed olefin arylations are summarized and discussed. The first one is Ir-catalyzed novel anti-Markovnikov hydroarylation of olefins with benzene. Using this reaction catalyzed by [Ir(μ-acac-O,O′,C₃)(acac-O,O′)(acac-C₃)]₂ (acac = acetylacetonato), 1, straight-chain alkylarenes, which were not obtainable by the conventional Friedel-Crafts aromatic alkylation with olefins, were able to be successfully synthesized directly from arenes and olefins with the higher selectivity than that of branched alkylarenes. This is the first efficient catalyst which shows the desirable high regioselectivity. The reaction of benzene with propylene gave n-propylbenzene and cumene in 61% and 39% selectivities, respectively, and the reaction of benzene and styrene afforded 1,2-diphenylethane in 98% selectivity. The reaction of alkylarene and olefin showed meta and para orientations. A wide range of olefins and arenes can be employed for the synthesis of alkylarenes. The mechanism of the reaction involves C–H bond activation of benzene by Ir center to form Ir–phenyl species. The second reaction is Rh-catalyzed oxidative arylation of ethylene with benzene to directly produce styrene, namely one-step synthesis of styrene. The reaction of benzene with ethylene catalyzed by Rh(ppy)₂(OAc) (ppyH = 2-phenylpyridine, OAc = acetate), 3 with Cu oxidizing agent gave styrene and vinyl acetate in 77% and 23% selectivities, respectively, in contrast to those by Pd(OAc)₂, 47% of styrene and 53% of vinyl acetate. The mechanism of the reaction involves Rh-mediated C–H bond activation of benzene, which appears to be a rate-determining step. Furthermore, Rh complexes in a Rh(I) oxidation state at the beginning of the reaction work as catalysts for the reaction by addition of acacH and O₂ without any oxidizing agent, like Cu salt.     

Use of water in aiding olefin/paraffin (liquid + liquid) extraction via complexation with a silver bis(trifluoromethylsulfonyl)imide salt

This paper describes the extraction of C₅–C₈ linear α-olefins from olefin/paraffin mixtures of the same carbon number via a reversible complexation with a silver salt (silver bis(trifluoromethylsulfonyl)imide, Ag[Tf₂N]) to form room temperature ionic liquids [Ag(olefin)_x][Tf₂N]. From the experimental (liquid + liquid) equilibrium data for the olefin/paraffin mixtures and Ag[Tf₂N], 1-pentene showed the best separation performance while C₇ and C₈ olefins could only be separated from the corresponding mixtures on addition of water which also improves the selectivity at lower carbon numbers like the C₅ and C₆, for example. Using infrared and Raman spectroscopy of the complex and Ag[Tf₂N] saturated by olefin, the mechanism of the extraction was found to be based on both chemical complexation and the physical solubility of the olefin in the ionic liquid ([Ag(olefin)_x][Tf₂N]). These experiments further support the use of such extraction techniques for the separation of olefins from paraffins.     

Towards a Practical Development of Light‐Driven Acceptorless Alkane Dehydrogenation

The efficient catalytic dehydrogenation of alkanes to olefins is one of the most investigated reactions in organic synthesis. In the coming years, an increased supply of shorter‐chain alkanes from natural and shale gas will offer new opportunities for inexpensive carbon feedstock through such dehydrogenation processes. Existing methods for alkane dehydrogenation using heterogeneous catalysts require harsh reaction conditions and have a lack of selectivity, whereas homogeneous catalysis methods result in significant waste generation. A strong need exists for atom‐efficient alkane dehydrogenations on a useful scale. Herein, we have developed improved acceptorless catalytic systems under optimal light transmittance conditions using trans‐[Rh(PMe₃)₂(CO)Cl] as the catalyst with different additives. Unprecedented catalyst turnover numbers are obtained for the dehydrogenation of cyclic and linear (from C₄) alkanes and liquid organic hydrogen carriers. These reactions proceed with unique conversion, thereby providing a basis for practical alkane dehydrogenations.     

Palladium(0) complexes coordinated with substituted olefins and tertiary phosphine ligands

New palladium(0) complexes with a variety of coordinated olefins [Pd(olefin)(PMePh₂)₂] (II) (olefin = styrene, ethyl methacrylate, methyl methacrylate, methyl acrylate, methacrylonitrile, and dimethyl maleate), were prepared by the reactions of [PdEt₂(PMePh₂)₂] (I) with corresponding olefins in toluene. These complexes were characterized by means of elemental analysis, IR and ¹H NMR spectroscopy and the chemical reactions. The dissociation of the coordinated olefin from complex II in solution was confirmed by spectroscopic studies of [Pd(mma)(PMePh₂)₂] (mma = methyl methacrylate). From the variable temperature NMR study, kinetic parameters for the dissociation process were determined as E_a = 7 kcal/mol, and ΔS³ (293 K) = -30 cal/deg · mol. Some new hydrido complexes, [Pd(H)ClL₂] (IV) (L = PMePh₂, PEtPh₂ and PEt₂Ph), were prepared by the reactions of [Pd(olefin)L₂] with dry HCl.     

The synthesis of a cationic ylide complex of platinum(II) by the reaction of tetrakis(triphenylphosphine)platinum(O) with choloroiodomethane.

The reaction of Pt(PPh₃)₄ with CH₂Cl1 in benzene yields the cationic ylide complex $\text{cis}$-[Pt(PPh₃)₂(CH₂PPh₃)Cl]I in high yield. This complex has been converted to $\text{cis}$-[(PPh₃)₂(CH₂PPh₃)X]X (X  Br or I) by reaction with LiBr or NaI. Reaction of $\text{cis}$-[Pt(PPH₃)I]I with iodine yields $\text{cis}$-[Pt(PPh₃)₂(CH₂PPh₃)I]I₃. Nmr data are given in support of the suggested structures.     

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.