Preparation of carboxylic arylphosphines by hydrolysis of the trifluoromethyl group

Triarylphosphines substituted with carboxylic and trifluoromethlyl groups have been prepared by the hydrolysis of trifluoromethyl groups using fuming sulfuric acid and boric acid. The reaction has been studied in a set of homoleptic and heteroleptic trifluoromethylated triarylphosphines and offers a new synthetic procedure for the preparation of carboxylic phosphines with a relatively simple methodology. The degree of carboxylation is modulated by the reaction conditions and is sensitive to the substitution pattern of the starting trifluoromethylated phosphines. A pH-dependent procedure based on the amphiphilic character of these phosphines was developed for their separation and purification. The electronic properties of the synthesized carboxylic-trifluoromethylated phosphines have been analyzed by 31P NMR of the corresponding selenide derivatives. Finally, the structures of two palladium complexes, containing the para and meta carboxylic-trifluoromethylated phosphines are also described, showing different dimeric structures.

Synthesis of Hydrophilic Phosphorus Ligands and Their Application in Aqueous-Phase Metal-Catalyzed Reactions

Transition metal-catalyzed reactions in aqueous media are experiencing a constant increase in interest. In homogenous catalysis the use of water as a solvent offers advantages in cost, safety, the possibility of two-phase catalysis and simplified separation strategies. In the life sciences, transition metal catalysis in aqueous systems enables the ligation or modification of biopolymers in buffer systems or even in their cellular environment. In biocatalysis, aqueous systems allow the simultaneous use of enzymes and transition metal catalysts in cascade reactions. The use of water-soluble phosphine ligands still represents the most reliable and popular strategy for transferring metal catalysts into the aqueous phase. This review summarizes the recent advancements in this field since 2009 and describes current synthetic strategies for the preparation of hydrophilic phosphines and phosphites. In addition, recent applications of transition metal catalysis in aqueous solvents using these hydrophilic ligands are presented.

Sulfonated Phosphine Ligands in the Ruthenium Catalyzed Biphasic Hydrogenation of Unsaturated Hydrocarbons

Abstract

The hydrogenation of monocyclic aromatic hydrocarbons by ruthenium catalysts has been investigated in the presence of sulfonated monophosphine ligands with different stereoelectronic properties under biphasic conditions. The effects of (i) the number of sulfonate groups, (ii) the steric demand of the ligand and (iii) the σ-donor ability of the phosphorus atom have been investigated in the catalytic reactions. The TEM analysis of the catalytically active systems revealed that in situ formed soluble ruthenium nanoparticles (RuNPs) are responsible for the catalytic turnover. The Ru/sulfonated phosphine system with the properly tuned ligand exhibited high activity (8800 h−1) and selectivity in the hydrogenation of benzene to cyclohexane. Furthermore, the aqueous phase containing RuNPs could be recycled four times without a considerable loss of activity.

Graphic Abstract

Rhodium(III) Complexes Featuring Coordinated CF3 Appendages

The synthesis and characterisation of a homologous series of rhodium 2,2'-biphenyl complexes featuring intramolecular dative bonding of the nominally inert and weakly coordinating trifluoromethyl group are described. Presence of these interactions is evidenced in the solid state using X-ray diffraction, with Rh-F contacts of 2.36-2.45 Å, and in solution using NMR spectroscopy, through hindered C-CF₃ bond rotation and the presence of time-averaged ¹ J_RhF and ² J_PF coupling.

Hydroformylation of unsaturated esters and 2,3-dihydrofuran under solventless conditions at room temperature catalysed by rhodium N-pyrrolyl phosphine catalysts

Complexes of the type HRh(CO)L₃ (where L is an N-pyrrolyl phosphine, e.g. P(NC₄H₄)₃, Ph(NC₄H₄)₂, or PPh₂(NC₄H₄)) were applied in the hydroformylation of less reactive unsaturated substrates (allyl acetate, butyl acrylate, methyl acrylate, 2,3-dihydrofuran, vinyl acetate).

Multiphasic aqueous hydroformylation of 1-alkenes with micelle-like polymer particles as phase transfer agents

Micelle-like polymer particles have been applied in aqueous multiphasic hydroformylation reactions of long chain alkenes. These colloids act as phase transfer agents for the nonpolar substrates and as carriers for the catalyst bearing sulfonated ligands by electrostatic attraction. The catalyst performance and the phase separation were optimized with special focus on the conversion, selectivity and catalyst recovery, as those are key points in multiphasic systems to achieve a feasible industrial process. The effect on the catalyst performance of the number of sulfonate groups and electron withdrawing trifluoromethyl groups in the ligand has been studied. The approach was successfully demonstrated for 1-alkenes from 1-hexene to 1-dodecene. For 1-octene, a TOF of more than 3000 h⁻¹ could be achieved at a substrate to catalyst ratio of 80 000, while keeping the rhodium and phosphorous leaching below 1 ppm. In repetitive batch experiments the catalyst was recycled four times, yielding an accumulated TON of more than 100 000 for 1-octene.

Micelle-like polyelectrolyte polymer particles were applied as phase transfer agents and catalyst carriers in the multiphasic hydroformylation of long chain alkenes achieving high turnover frequencies and efficient catalyst recovery.

Improved Deconvolution of Protein Targets for Bioactive Compounds Using a Palladium Cleavable Chloroalkane Capture Tag

The benefits provided by phenotypic screening of compound libraries are often countered by difficulties in identifying the underlying cellular targets. We recently described a new approach utilizing a chloroalkane capture tag, which can be chemically attached to bioactive compounds to facilitate the isolation of their respective targets for subsequent identification by mass spectrometry. The tag minimally affects compound potency and membrane permeability, enabling target engagement inside cells. Effective enrichment of these targets is achieved through selectivity in both their rapid capture onto immobilized HaloTag and their subsequent release by competitive elution. Here, we describe a significant improvement to this method where selective elution was achieved through palladium-catalyzed cleavage of an allyl-carbamate linkage incorporated into the chloroalkane capture tag. Selective tag cleavage provided robust release of captured targets exhibiting different modes of binding to the bioactive compound, including prolonged residence time and covalent interactions. Using the kinase inhibitors ibrutinib and BIRB796 as model compounds, we demonstrated the capability of this new method to identify both expected targets and "off-targets" exhibiting a range of binding affinities, cellular abundances, and binding characteristics.

Synthesis of Dendrimers with a Bidentate Phosphine Core Ligand Having Carboxy Groups at the Peripheral Layer and Their Application to Aqueous Media Cross-Coupling Reactions

We prepared a series of dendrimers with a bidentate phosphine core ligand having carboxy groups at the peripheral layer. By employing the corresponding water-soluble dendritic phosphine-palladium complex as a catalyst, the aqueous media Suzuki-Miyaura reaction and Tsuji-Trost reaction proceeded to provide the corresponding cross-coupling product.

A self-emulsifying catalytic system for the aqueous biphasic hydroformylation of triglycerides

The Rh-catalyzed hydroformylation of the CC double bonds of triglycerides (T) was performed in aqueous medium through the formation of supramolecular complexes resulting from the inclusion of the alkenyl chains of T into the cavity of modified cyclodextrins (CDs).