Introducing TPPTS and related ligands for industrial biphasic processes

Ubiquitous Role of Phosphine-Based Water-Soluble Ligand in Promoting Catalytic Reactions in Water

Catalysis has been at the forefront of the developments that has revolutionised synthesis and provided the impetus in the discovery of platform technologies for efficient C-C or C-X bond formation. Current environmental situation however, demands a change in strategy with catalysis being promoted more in solvents that are benign (Water) and for that the development of hydrophilic ligands (especially phosphines) is a necessity which could promote catalytic reactions in water, allow recyclability of the catalytic solutions and make it possible to isolate products using column-free techniques that involve lesser usage of hazardous organic solvents. In this review, we therefore critically analyse such catalytic processes providing examples that do follow the above-mentioned parameter.

Synthesis Strategies towards Tagged Homogeneous Catalysts To Improve Their Separation

The recycling of homogeneous catalysts while keeping them in the homogeneous matrix is an ongoing challenge many reactions face if they are to find industrial applications. While a plethora of different synthetic approaches towards better, recyclable homogeneous catalysts exist, the literature shows a gap when one searches for a concise overview of the different catalyst modifications. This Review is designed to close that gap by summarising the existing synthesis pathways towards polar, non-polar, fluorous, and molecular-weight-enlarged catalysts and by examining their respective synthesis routes with a focus on modular and late-stage approaches. Furthermore, we map out the potential for a generally applicable tag library that allows straightforward catalyst modifications to tune them for each desired recycling strategy.

Covalent Modification of Nucleobases using Water-Soluble Palladium Catalysts

Nucleosides represent one of the key building blocks of biochemistry. There is significant interest in the synthesis of nucleoside-derived materials for applications as probes, biochemical models, and pharmaceuticals. Palladium-catalyzed cross-coupling reactions are effective methods for making covalent modification of carbon and nitrogen sites on nucleobases under mild conditions. Water-soluble catalysts derived from palladium and hydrophilic ligands, such as tris(3-sulfonatophenyl)phosphine trisodium (TPPTS), are efficient catalysts for a range of coupling reactions of unprotected halonucleosides. Over the past two decades, these methods have been extended to direct functionalization of halonucleotides, as well as RNA and DNA oligonucleotides (ONs) containing halogenated bases. These methods can be run under biocompatible conditions, including examples of Suzuki coupling of modified DNA in whole cells and tissue samples. In this account, development of this methodology by our group and others is highlighted along with the extension of these catalyst systems to modification of nucleotides and ONs.

Proof of Concept: Interface of Recyclable Organogels with Embedded Palladium Nanoparticles Catalyzing Suzuki-Miyaura Coupling in Water at Room Temperature

A sustainable approach for C-C cross-coupling reaction at room temperature in water has been developed to avoid tedious Pd separation, reduce the carbon footprint, and save energy. Another important aspect is the catalyst recycling and easy product separation. α,γ-Hybrid peptides were designed to selectively use as a ligand for C-C cross-coupling catalysts as well as to form organogels. The peptides form antiparallel sheet-like structures in the solid state. The peptide containing m-aminobenzoic acid, glycine, and dimethylamine forms a whitish gel in toluene, and co-gelation with Pd(OAc)2 results in light brown gel, which acts as a biphasic catalyst for Suzuki-Miyaura cross-coupling at room temperature in water by mild shaking. The organic-inorganic hybrid gel was characterized by rheology, field-emission scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray analyses. On completion of the cross-coupling reaction, the basic aqueous layer (containing products) above the gel can be simply decanted and the intact organic-inorganic hybrid gel can be recycled by topping-up fresh reactants multiple times. The reaction permitted a range of different substitution patterns for aryl and heterocyclic halides with acid or phenol functional groups. Both electron-donating- and electron-withdrawing-substituted substrates exhibited good results for this transformation. The findings inspire toward a holistic green technology for Suzuki-Miyaura coupling reaction and an innovative avenue for catalyst recycling and product isolation.

Regio-Selective C3- and N-Alkylation of Indolines in Water under Air Using Alcohols

We disclosed a regio-selective C-H and N-H bond functionalization of indolines using alcohols in water via tandem dehydrogenation of N-heterocycles and alcohols. A diverse range of N- and C3-alkylated indolines/indoles were accessed utilizing a new cooperative iridium catalyst. The practical applicability of this methodology was demonstrated by the preparative-scale synthesis and synthesis of a psychoactive drug, N,N-dimethyltryptamine. A catalytic cycle is proposed based on several kinetic experiments, series of control experiments and density functional theory calculations.

Auto-tandem catalytic reductive hydroformylation with continuous multiphase catalyst recycling

This work covers auto-tandem catalytic hydroformylation and hydrogenation for the synthesis of alcohols for synthetic fuels from renewable olefin cuts. A multiphase catalyst recycling system was proven to be feasible in continuous flow.

Green Process Design for Reductive Hydroformylation of Renewable Olefin Cuts for Drop-In Diesel Fuels

CO2 -neutral fuels are a way to cleaner and more sustainable mobility. Utilization of bio-syngas via Fischer-Tropsch (FT) synthesis represents an interesting route for the production of tailormade biofuels. Recent developments in FT catalyst research led to olefin-enriched products, enabling the synthesis of alcohol-enriched fuels by reductive hydroformylation of the C=C bond. Several alcohols have already proven to be suitable fuel additives with favorable combustion behavior. Here, a hydroformylation-hydrogenation sequence of FT-olefin-paraffin mixtures was investigated as a potential route to alcohols. A liquid-liquid biphasic system with a rhodium/3,3',3''-phosphanetriyltris(benzenesulfonic acid) trisodium salt (TPPTS) catalyst system was chosen for effective catalyst recycling. After optimizing reaction conditions with a model substrate consisting of 1-octene and n-heptane the conversion of an actual olefin-containing C5 -C10  FT product fraction to alcohols in continuously operated processes for 37 h was achieved with a total turnover number of 23679.

Synthesis of Nixantphos Core-Functionalized Amphiphilic Nanoreactors and Application to Rhodium-Catalyzed Aqueous Biphasic 1-Octene Hydroformylation

A latex of amphiphilic star polymer particles, functionalized in the hydrophobic core with nixantphos and containing P(MAA-co-PEOMA) linear chains in the hydrophilic shell (nixantphos-functionalized core-crosslinked micelles, or nixantphos@CCM), has been prepared in a one-pot three-step convergent synthesis using reversible addition-fragmentation chain transfer (RAFT) polymerization in water. The synthesis involves polymerization-induced self-assembly (PISA) in the second step and chain crosslinking with di(ethylene glycol) dimethacrylate (DEGDMA) in the final step. The core consists of a functionalized polystyrene, obtained by incorporation of a new nixantphos-functionalized styrene monomer (nixantphos-styrene), which is limited to 1 mol%. The nixantphos-styrene monomer was synthesized in one step by nucleophilic substitution of the chloride of 4-chloromethylstyrene by deprotonated nixantphos in DMF at 60 °C, without interference of either phosphine attack or self-induced styrene polymerization. The polymer particles, after loading with the [Rh(acac)(CO)₂] precatalyst to yield Rh-nixantphos@CCM, function as catalytic nanoreactors under aqueous biphasic conditions for the hydroformylation of 1-octene to yield n-nonanal selectively, with no significant amounts of the branched product 2-methyl-octanal.

Bio-inspired creation of heterogeneous reaction vessels via polymerization of supramolecular ion pair

Precise control of the outer-sphere environment around the active sites of heterogeneous catalysts to modulate the catalytic outcomes has long been a challenge. Here, we demonstrate how this can be fulfilled by encapsulating catalytic components into supramolecular capsules, used as building blocks for materials synthesis, whereby the microenvironment of each active site is tuned by the assembled wall. Specifically, using a cationic template equipped with a polymerizable functionality, anionic ligands can be encapsulated by ion pair-directed supramolecular assembly, followed by construction into porous frameworks. The hydrophilic ionic wall enables reactions to be achieved in water that usually requires organic solvents and also facilitates the enrichment of the substrate into the hydrophobic pocket, leading to superior catalytic performances as demonstrated by the industrially relevant hydroformylation. Remarkably, the formation of the supramolecular assembly and catalyst encapsulation further engenders reaction selectivity, which reaches an even greater extent after construction of the porous framework.

Tuning the environment of catalytic active sites may improve the selectivity of heterogeneous catalysts. Here, the authors modify the outer-sphere environment of active sites in hydroformylation catalysts by encapsulating the active sites in nanovessels formed by ion pair-directed supramolecular assembly.

Homogeneous hydroformylation of long chain alkenes catalyzed by water soluble phosphine rhodium complex in CH3OH and efficient catalyst cycling

The hydroformylation of long chain alkenes catalyzed by a water soluble Rh/TPPTS complex (TPPTS: sodium salt of sulfonated triphenylphosphine) in methanol was investigated. The mixture of rhodium precursor HRh(CO)(TPPTS)₃, ligand TPPTS, methanol and a long chain alkene becomes a single phase under reaction conditions, which make the hydroformylation reaction proceed homogeneously. Both the conversion of long chain alkene and the selectivity to aldehydes (including the aldehydes forming methylacetals) could reach up to 97.8% and 97.6%, respectively, with 3323 h⁻¹ of TOF (TOF: turnover frequency is defined as the moles of converted alkene per mole of Rh per hour). After the solvent methanol was removed under the reaction temperature, two phases were formed automatically. The colourless product phase could be efficiently separated from the precipitate rhodium catalyst phase by centrifuge. The catalyst was reused for five times without obvious loss of rhodium and the catalytic activity. The rhodium leaching in product mixture was less than 0.03% of the total rhodium.

Hydroformylation of long-chain alkenes proceeded homogeneously in methanol efficiently. The catalyst could be separated heterogeneously when methanol was removed and recycled for four times without obvious loss in catalytic performance and rhodium.

Synthesis and Single Crystal X-Ray Structure of N,N′-Bis(Diphenylphosphino)Piperazine

The reaction of piperazine with chlorodiphenylphosphine in toluene under refluxing conditions yields Ph2PN(C4H8)NPPh2 in quantitative yield. The structure is confirmed by single crystal X-ray diffraction studies.

Butanol Synthesis Routes for Biofuel Production: Trends and Perspectives

Butanol has similar characteristics to gasoline, and could provide an alternative oxygenate to ethanol in blended fuels. Butanol can be produced either via the biotechnological route, using microorganisms such as clostridia, or by the chemical route, using petroleum. Recently, interest has grown in the possibility of catalytic coupling of bioethanol into butanol over various heterogenic systems. This reaction has great potential, and could be a step towards overcoming the disadvantages of bioethanol as a sustainable transportation fuel. This paper summarizes the latest research on butanol synthesis for the production of biofuels in different biotechnological and chemical ways; it also compares potentialities and limitations of these strategies.

Homogeneous Catalysis and Mechanisms in Water and Biphasic Media

After its discovery in the early 1980s and successful application on an industrial scale (Ruhrchemie/Rhone-Poulenc process) [...]

Synthesis, Structural Characterization and Catalytic Evaluation of Anionic Phosphinoferrocene Amidosulfonate Ligands

Triethylammonium salts of phosphinoferrocene amidosulfonates with electron-rich dialkyphosphino substituents, R2PfcCONHCH2SO3(HNEt3) (4a–c), where fc = ferrocene-1,1′-diyl, and R = i-Pr (a), cyclohexyl (Cy; b), and t-butyl (c), were synthesized from the corresponding phosphinocarboxylic acids-borane adducts, R2PfcCO2H·BH3 (1a–c), via esters R2PfcCO2C6F5·BH3 (2a–c) and adducts R2PfcCONHCH2SO3(HNEt3)·BH3 (3a–c). Compound 4b was shown to react with [Pd(μ-Cl)(η-C3H5)]2 and AgClO4 to afford the zwitterionic complex [Pd(η3-C3H5)(Cy2PfcCONHCH2SO3-κ2O,P)] (5b), in which the amidosulfonate ligand coordinates as a chelating donor making use of its phosphine moiety and amide oxygen. The structures of 3b·CH2Cl2, 4b and 5b·CH2Cl2 were determined by single-crystal X-ray diffraction analysis. Compounds 4a–c and their known diphenylphosphino analogue, Ph2PfcCONHCH2SO3(HNEt3) (4d), were studied as supporting ligands in Pd-catalyzed cyanation of aryl bromides with K4[Fe(CN)6] and in Suzuki–Miyaura biaryl cross-coupling performed in aqueous reaction media under mild reaction conditions. In the former reaction, the best results were achieved with a catalyst generated from [PdCl2(cod)] (cod = η2:η2-cycloocta-1,5-diene) and 2 equiv. of the least electron-rich ligand 4d in dioxane–water as a solvent. In contrast, the biaryl coupling was advantageously performed with a catalyst resulting from palladium(II) acetate and ligand 4a (1 equiv.) in the same solvent.

Transition Metal Complexes Coordinated by Water Soluble Phosphane Ligands: How Cyclodextrins Can Alter the Coordination Sphere?

The behaviour of platinum(II) and palladium(0) complexes coordinated by various hydrosoluble monodentate phosphane ligands has been investigated by ³¹P{¹H} NMR spectroscopy in the presence of randomly methylated β-cyclodextrin (RAME-β-CD). This molecular receptor can have no impact on the organometallic complexes, induce the formation of phosphane low-coordinated complexes or form coordination second sphere species. These three behaviours are under thermodynamic control and are governed not only by the affinity of RAME-β-CD for the phosphane but also by the phosphane stereoelectronic properties. When observed, the low-coordinated complexes may be formed either via a preliminary decoordination of the phosphane followed by a complexation of the free ligand by the CD or via the generation of organometallic species complexed by CD which then lead to expulsion of ligands to decrease their internal steric hindrance.

Water-soluble metal nanoparticles stabilized by plant polyphenols for improving the catalytic properties in oxidation of alcohols

Plant polyphenols extracted from plants are one of the most abundant biomasses in nature, which are typical water soluble natural polymers. Herein, we reported a facile approach for the synthesis of platinum nanoparticle (PtNP) aqueous colloid by utilizing black wattle tannin (BWT, a typical plant polyphenol) as amphiphilic stabilizer. The phenolic hydroxyls of BWT provide the PtNPs with enough hydrophilicity, and their reduction ability could protect the PtNPs from deactivation caused by oxygen atmosphere. Additionally, the hydrophilic nature of BWT could efficiently promote the oxidation of alcohols in water, meanwhile, the hydrophobic and rigid backbones of plant polyphenols are able to suppress the PtNPs from aggregating, thus ensuring the high dispersion of the PtNPs during reactions. Under mild aerobic conditions, the as-prepared BWT-Pt colloid catalyst exhibited high activity in a series of biphasic oxidation of aromatic alcohols and aliphatic alcohols. As for the cycling stability, the BWT-Pt catalyst showed no obvious decrease during the 7 cycles, revealing superior cycling stability as compared with the counterparts using PVP or PEG as the stabilizer.

Recoverable and recyclable water-soluble sulphonated salicylaldimine Rh(i) complexes for 1-octene hydroformylation in aqueous biphasic media

A series of water-soluble Rh(i) mononuclear complexes of general formula: [Rh(sulphsal-X-R)(COD)] [sulphsal = sulphonated salicylaldimine, COD = cyclooctadiene; where R = H, Cl, CH₃ and X = H, ^tBu] have been synthesized.