Phosphoric Acid Ligand Research Articles

Reticular Chemistry in Its Chiral Form: Axially Chiral Zr(IV)-Spiro Metal-Organic Framework as a Case Study.

The interplay of primary organic ligands and inorganic secondary building units (SBUs) has led to a continual boom of reticular chemistry, particularly metal-organic frameworks (MOFs). Subtle variations of organic ligands can have a significant impact on the ultimate structural topology and consequently, the material's function. However, the role of ligand chirality in reticular chemistry has rarely been explored. In this work, we report the organic ligand chirality-controlled synthesis of two zirconium-based MOFs (Spiro-1 and Spiro-3) with distinct topological structures as well as a temperature-controlled formation of a kinetically stable phase (Spiro-4) based on the carboxylate-functionalized inherently axially chiral 1,1'-spirobiindane-7,7'-phosphoric acid ligand. Specifically, Spiro-1 is a homochiral framework comprising only enantiopure S-spiro ligands and has a unique 4,8-connected sjt topology with large 3D interconnected cavities, while Spiro-3 contains equal amounts of S- and R-spiro ligands, resulting in a racemic framework of 6,12-connected edge-transitive alb topology with narrow channels. Interestingly, the kinetic product Spiro-4 obtained with racemic spiro ligands is built of both hexa- and nona-nuclear zirconium clusters acting as 9- and 6-connected nodes, respectively, giving rise to a newly discovered azs net. Notably, the preinstalled highly hydrophilic phosphoric acid groups combined with large cavity, high porosity, and outstanding chemical stability endow Spiro-1 with remarkable water vapor sorption performance, whereas Spiro-3 and Spiro-4 show poor performances due to inappropriate pore systems and structural fragility upon the water adsorption/desorption process. This work highlights the important role of ligand chirality in manipulating the framework topology and function and would further enrich the development of reticular chemistry.

Palladium-Catalyzed Regioselective B(3,4)-H Acyloxylation of o-Carboranes.

We disclose herein an efficient regioselective B(3,4)-H activation via a ligand strategy, affording B(3)-monoacyloxylated and B(3,4)-diacyloxylated o-carboranes. The identification of amino acid and phosphoric acid ligands is crucial for the success of B(3)-mono- and B(3,4)-diacyloxylation, respectively. This ligand approach is compatible with a broad range of carboxylic acids. The functionalization of complex drug molecules is demonstrated. Other acyloxyl sources, including sodium benzoate, benzoic anhydride, and iodobenzene diacetate, are also tolerated.

Understanding Self-Assembly and the Stabilization of Liquid/Liquid Interfaces: The Importance of Ligand Tail Branching and Oil-Phase Solvation

HypothesisOrganophosphorus-based ligands represent a versatile set of solvent extraction reagents whose chemical makeup plays an important role in extraction mechanism. We hypothesize that the branching of the extractant hydrophobic tail and its oil-phase solvation affect the liquid/liquid interfacial structure. Understanding the structure mediated adsorption and interfacial ordering becomes key in designing ligands with enhanced selectivity and efficiency for targeted extractions. ExperimentWe employed vibrational sum frequency generation spectroscopy and interfacial tension measurements to extract thermodynamic adsorption energies, map interfacial ordering, and rationalize disparate behaviors of model di-(2-ethylhexyl) phosphoric acid and dioctyl phosphoric acid ligands at the hexadecane water interface. FindingsWith increased surface loading, ligands with branched hydrophobic tails formed stable interfaces at much lower concentrations than those observed for ligands with linear alkyl tails. The lack of an oil phase and associated solvation results in markedly different interfacial properties, and thus measurements made at air/liquid surfaces cannot be assumed to correlate with the processes occurring at buried liquid/liquid interfaces. We attribute these differences in the surface mediated self-assembly to key variations in hydrophobic interactions and tail solvation taking place in the oil phase demonstrating that interactions in both the polar and nonpolar phases are essential to understand self-assembly and function.

Constructing proton transport channels in low phosphoric-acid doped polybenzimidazole membrane by introducing metal–organic frameworks containing phosphoric-acid groups

Proton-exchange membranes (PEMs) are considered as core components of high-temperature fuel cells. Phosphoric acid (PA) plays a pivotal role in the performance of PEMs and is especially vital for conductivity. This work reports the firstly successful preparation of metal–organic frameworks grafted with phosphate functionalized ligand, which introduce efficient, high-performance proton transport channels. At a ligand replacement ratio of 1:2, the conductivity of 40% hydroxyphosphono-acetic acid-type UIO-66@OPBI membrane is 0.097 S cm −1 at 160 °C (0% RH), and the power density of the fuel cell achieves 640 mW cm −2 . When the UIO-66 ligand is replaced with glyphosine containing two phosphate groups at the same ratio (1:2, 40% composition), the highest conductivity of the composite membrane is 0.124 S cm −1 , and the power density of the fuel cell reaches 725 mW cm −2 at 160 °C (0% RH). The composite membrane fuel-cell stably withstand a constant current discharge of 200 mA cm −2 for 200 h (160 °C, 0% RH) with a voltage attenuation rate of only 0.042 mV h −1 from 60 to 200 h, lower than that of the 1:2H–UIO-66@OPBI membrane (0.066 mV h −1 ) under the same conditions. • Metal–organic frameworks (MOF) grafted with phosphoric acid ligand is synthesized. • The unique MOF greatly enhances performance of phosphoric acid doped PBI membrane. • 1:2G–UIO-66@OPBI HT-PEM achieves the highest proton conductivity (0.124 S cm −1 . • The HR-PEM fuel cell exhibits an excellent long-term stability. • The HR-PEM fuel cell achieves a peak power density 725 mW cm −2 at 160 °C (0% RH).

Interfacial structure in the liquid-liquid extraction of rare earth elements by phosphoric acid ligands: a molecular dynamics study.

Solvent extraction (SX), wherein two immiscible liquids, one containing the extractant molecules and the other containing the solute to be extracted are brought in contact to effect the phase transfer of the solute, underpins metal extraction and recovery processes. The interfacial region is of utmost importance in the SX process, since besides thermodynamics, the physical and chemical heterogeneity at the interface governs the kinetics of the process. Yet, a fundamental understanding of this heterogeneity and its implications for the extraction mechanism are currently lacking. We use molecular dynamics (MD) simulations to study the liquid-liquid interface under conditions relevant to the SX of Rare Earth Elements (REEs) by a phosphoric acid ligand. Simulations revealed that the extractant molecules and varying amounts of acid and metal ions partitioned to the interface. The presence of these species had a significant effect on the interfacial thickness, hydrogen bond life times and orientations of the water molecules at the interface. Deprotonation of the ligands was essential for the adsorption of the metal ions at the interface, with these ions forming a number of different complexes at the interface involving one to three extractant molecules and four to eight water molecules. Although the interface itself was rough, no obvious 'finger-like' water protrusions penetrating the organic phase were seen in our simulations. While the results of our work help us gain fundamental insights into the sequence of events leading to the formation of a variety of interfacial complexes, they also emphasize the need to carry out a more detailed atomic level study to understand the full mechanism of extraction of REEs from the aqueous to organic phases by phosphoric acid ligands.

Why the Reactive Oxygen Species of the Fenton Reaction Switches from Oxoiron(IV) Species to Hydroxyl Radical in Phosphate Buffer Solutions? A Computational Rationale.

It has been shown that the major reactive oxygen species (ROS) generated by the aqueous reaction of Fe(II) and H2O2 (i.e., the Fenton reaction) are high-valent oxoiron(IV) species, whereas the hydroxyl radical plays a role only in very acidic conditions. Nevertheless, when the Fenton reaction is conducted in phosphate buffer solutions, the resulting ROS turns into hydroxyl radical even in neutral pH conditions. The present density functional theory (DFT) study discloses the underlying principle for this phenomenon. Static and dynamic DFT calculations indicate that in phosphate buffer solutions, the iron ion is highly coordinated by phosphoric acid anions. Such a coordination environment substantially raises the pKa of coordinated water on Fe(III). As a consequence, the Fe(III)–OH intermediate, resulting from the reductive decomposition of H2O2 by ferrous ion is relatively unstable and will be readily protonated by phosphoric acid ligand or by free proton in solution. These proton-transfer reactions, which become energetically favorable when the number of phosphate coordination goes up to three, prevent the Fe(III)–OH from hydrogen abstraction by nascent •OH to form Fe(IV)=O species. On the basis of this finding, a ligand design strategy toward controlling the nature of ROS produced in the Fenton reaction is put forth. In addition, it is found that while phosphate buffers facilitate •OH radical generation in the Fenton reaction, phosphoric acid anions can act as •OH radical scavengers through hydrogen atom transfer reactions.

Enantioselective Synthesis of Biaryl Atropisomers by Pd-Catalyzed C-H Olefination using Chiral Spiro Phosphoric Acid Ligands.

The discovery of proper ligands to simultaneously modulate the reactivity and effectively control the stereoselectivity is a central topic in the field of enantioselective C-H activation. Herein, we reported the synthesis of axially chiral biaryls by Pd-catalyzed atroposelective C-H olefination. A novel chiral spiro phosphoric acid, STRIP, was identified as a superior ligand for this transformation. A broad range of axially chiral quinoline derivatives were synthesized in good yields with excellent enantioselectivities (up to 98 % ee). Density functional theory was used to gain a theoretical understanding of the enantioselectivities in this reaction.

Enantioselective Synthesis of Biaryl Atropisomers by Pd‐Catalyzed C−H Olefination using Chiral Spiro Phosphoric Acid Ligands

AbstractThe discovery of proper ligands to simultaneously modulate the reactivity and effectively control the stereoselectivity is a central topic in the field of enantioselective C−H activation. Herein, we reported the synthesis of axially chiral biaryls by Pd‐catalyzed atroposelective C−H olefination. A novel chiral spiro phosphoric acid, STRIP, was identified as a superior ligand for this transformation. A broad range of axially chiral quinoline derivatives were synthesized in good yields with excellent enantioselectivities (up to 98 % ee). Density functional theory was used to gain a theoretical understanding of the enantioselectivities in this reaction.

Differential Stabilization of the Metal–Ligand Complexes between Organic and Aqueous Phases Drives the Selectivity of Phosphoric Acid Ligands toward Heavier Rare Earth Elements

Rare earth elements (REEs) are widely used in several electrical and electronic devices and emerging technologies. With increase in demand of REEs, their recovery from electronic wastes, through hydrometallurgical routes, is a promising alternate source of these elements over conventional mining processes. In a number of experiments, organophosphoric acid ligands such as bis-2-ethylhexyl phosphoric acid (D2EHPA) and 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (EHEHPA) have shown high selectivity toward heavier REEs. While the general extraction equilibrium is well established, an atomistically detailed understanding of the origin of this selectivity is still lacking. We use molecular dynamics simulations to elucidate the structure of the Nd- and Dy-D2EPHA complexes in vacuum, aqueous, and organic phases and show that the selectivity of D2EHPA for Dy arises from the favorable differential stabilization of the complex in the solvent phases, caused by the structural features of the Dy-D2EHPA complex....

Palladium-Catalyzed Enantioselective C-H Activation of Aliphatic Amines Using Chiral Anionic BINOL-Phosphoric Acid Ligands.

The design of an enantioselective Pd(II)-catalyzed C-H amination reaction is described. The use of a chiral BINOL phosphoric acid ligand enables the conversion of readily available amines into synthetically valuable aziridines in high enantiomeric ratios. The aziridines can be derivatized to afford a range of chiral amine building blocks incorporating motifs readily encountered in pharmaceutically relevant molecules.

An Enantioselective Bidentate Auxiliary Directed Palladium‐Catalyzed Benzylic C−H Arylation of Amines Using a BINOL Phosphate Ligand

AbstractA new enantioselective palladium(II)‐catalyzed benzylic C−H arylation reaction of amines is enabled by the bidentate picolinamide (PA) directing group. This reaction provides the first example of enantioselective benzylic γ‐C−H arylations of alkyl amines, and proceeds with up to 97 % ee. The 2,2′‐dihydroxy‐1,1′‐binaphthyl (BINOL) phosphoric acid ligand, Cs2CO3, and solvent‐free conditions are essential for high enantioselectivity. Mechanistic studies suggest that multiple BINOL ligands are involved in the stereodetermining C−H palladation step.

An Enantioselective Bidentate Auxiliary Directed Palladium-Catalyzed Benzylic C-H Arylation of Amines Using a BINOL Phosphate Ligand.

A new enantioselective palladium(II)-catalyzed benzylic C-H arylation reaction of amines is enabled by the bidentate picolinamide (PA) directing group. This reaction provides the first example of enantioselective benzylic γ-C-H arylations of alkyl amines, and proceeds with up to 97 % ee. The 2,2'-dihydroxy-1,1'-binaphthyl (BINOL) phosphoric acid ligand, Cs2 CO3 , and solvent-free conditions are essential for high enantioselectivity. Mechanistic studies suggest that multiple BINOL ligands are involved in the stereodetermining C-H palladation step.

ChemInform Abstract: Enantioselective Synthesis of Tetrahydroindolizines via Ruthenium‐Chiral Phosphoric Acid Sequential Catalysis.

AbstractA chiral BINOL‐derived phosphoric acid ligand and Ru complex Zhan‐1B catalyze sequential olefin cross‐metathesis and asymmetric intramolecular Friedel‐Crafts alkylation reactions in modest to good yields with good enantioselectivities.

Synthesis and structures of a chiral phosphine–phosphoric acid ligand and its rhodium(I) complexes

The synthesis and characterization of a novel chiral phosphine–phosphoric acid ligand, (R)-3-diphenylphosphino-1,1′-binaphthyl-2,2′-diyl hydrogenphosphate (2) and its rhodium(I) complexes are described. The single-crystal X-ray diffraction analysis of 2 showed the intermolecular hydrogen-bonding network of the phosphoric acid moiety. The reactions of 2 with [RhCl(cod)]2 in the presence of KOtBu or with [Rh(acac)(CO)2] (acac=acetylacetonate) gave P,O-chelating rhodium(I) complexes [Rh(2–H+)(cod)] 3 or [Rh(2–H+)(CO)]24, respectively. Their molecular structures were determined by single-crystal X-ray diffraction.

ChemInform Abstract: Catalytic Asymmetric Functionalization of Aromatic C—H Bonds by Electrophilic Trapping of Metal‐Carbene‐Induced Zwitterionic Intermediates.

AbstractThe rhodium‐catalyzed three‐component reaction between N,N‐disubstituted anilines, α‐diazoarylacetic esters and diarylimines in the presence of (R)‐BINOL‐derived phosphoric acid ligand TBP gives compounds with quaternary stereocenters in good yield with high diastereo‐ and enantioselectivities.

Development of a new ion-exchange/coordinating phosphate ligand for the sorption of U(VI) and trivalent ions from phosphoric acid solutions

A polymer-bound monoprotic phosphoric acid ligand was developed for the sorption of U(VI) from 0.10 to 6.0M phosphoric acid solutions. The ligands reported are new phosphorylated mono- and triethylene glycol ethyl esters (pEG1M and pEG3M) prepared by combining diethylchlorophosphate and 4-dimethylaminopyridine; they ion exchange through the acid site and coordinate through the phosphoryl oxygen. The binding mechanism is probed by comparing their results to coordinating phosphorylated mono- and triethylene glycol diethyl esters (pEG1 and pEG3) and the diprotic phosphonic acid (DPA) that operates by ion exchange. The affinities for Lu(III), La(III), Fe(III) and Al(III) were also determined. All metal ions were sorbed much more efficiently by the monoprotic ligand relative to the diprotic and coordinating ligands. It is proposed that a decrease in inter-ligand hydrogen bonding within the monoprotic ligand is responsible for the increased metal ion affinities. This is consistent with the FTIR spectra wherein the P=O band appears at 1262cm−1 for pEG1 and this shifts down to 1229cm−1 in pEG1M and 1180cm−1 for DPA. Incorporating ether oxygen into the ligand further enhances metal affinities: pEG3M with three oxygen donors adjacent to the monoprotic site shows the highest affinity for metal ions. The increased affinities compared to pEG1M are due to complexation by the weakly binding ether oxygen donors. High metal ion affinities thus require both ion exchange with acidic protons and coordination with neutral donors. More rapid kinetics evident with pEG3M relative to DPA is further evidence for decreased hydrogen bonding which permits more rapid sorption. The affinity orders of the three acidic polymers are similar: U(VI), Lu(III)>Fe(III) >La(III)>Al(III). Ligand strength is pEG3M>pEG1M>DPA>pEG3>pEG1.

Synthesis, Characterization, Fluorescence and Antibacterial Activity of the Re(VII) Complex [ReO3(phen)(H2PO4)]・H2O

Single crystals of a Re(VII) complex, the dihydrogenophosphato phenanthroline trioxo-rhenium monohydrate of formula [ReO3(phen)(H2PO4)]⋅H2O (phen=1,10-phenanthroline), were prepared in aqueous solution. X-Ray analysis shows that it crystallizes in the monoclinic space group P21/c with the unit cell parameters: a=8.611(2), b=13.881(2), c=14.502(4) Å , β =120:87(2)°, V =1487.9(6) Å3 and Z = 4. In the neutral complex, the rhenium is in the oxidation state +VII, coordinated by two nitrogen atoms of the bidentate phen, three terminal oxygen atoms and, for the first time, one oxygen atom of the mono-deprotonated phosphoric acid ligand H2PO- 4 , forming a squarebased bipyramidal coordination geometry. The thermal stability, IR, UV/Vis and fluorescence spectroscopic properties are given. The complex shows antimicrobial activity against five different microbes.

Self-assembly of di- and triorganotin(IV) complexes: Syntheses, characterization and crystal structures of 1D polymeric chain containing O, O-diethyl or O, O-diisopropyl phosphoric acid ligands

A series of organotin(IV) complexes with O, O-diethyl phosphoric acid (L 1H) and O, O-diisopropyl phosphoric acid (L 2H) of the types: [R 3Sn · L] n (L = L 1, R = Ph 1, R = PhCH 2 2, R = Me 3, R = Bu 4; L = L 2, R = Ph 9, R = PhCH 2 10, R = Me 11, R = Bu 12), [R 2Cl Sn · L] n (L = L 1, R = Me 5, R = Ph 6, R = PhCH 2 7, R = Bu 8; L = L 2, R = Me 13, R = Ph 14, R = PhCH 2 15, R = Bu 16), have been synthesized. All complexes were characterized by elemental analysis, TGA, IR and NMR ( 1H, 13C, 31P and 119Sn) spectroscopy analysis. Among them, complexes 1, 2, 3, 5, 8, 9 and 11 have been characterized by X-ray crystallography diffraction analysis. In the crystalline state, the complexes adopt infinite 1D infinite chain structures which are generated by the bidentate bridging phosphonate ligands and the five-coordinated tin centers.

Functionalized Solvents for Olefin Isomer Purification by Reactive Extractive Distillation

Olefin isomer separations are difficult, energy intensive and thus expensive. An overview is presented to investigate the feasibility of metal–ligand complexes as functionalized solvents applied in a novel separation technology, reactive extractive distillation, for the separation and purification of α-olefins like 1-hexene from other C6-olefin isomers (internal, branched, cyclic and diolefins) and paraffins by using π-complexation. Functionalized metal–ligand complexes were synthesized based on commercial available ligands from hydrometallurgy. In screening experiments they were evaluated for ρ-complexation with ethylene. The best solvents were selected for evaluation of preferential complexation of 1-hexene relative to other olefin isomers. D2EHPA and DNNSA yield both stable metal–ligand complexes and triple the solubility of ethylene. Next, three different phosphoric acid ligands: D2EHPA, DBPA and MEHPA and two sulphonic acid ligands: DNNSA and DBSA, were investigated for a variety of C6-olefin isomers. The highest selectivities were obtained for silver-DBPA (20 wt% Ag, S/ F = 3): 1.23 for 2-methyl-1-pentene and 1.42 for n-hexane. An equilibrium model is used to conceptually design a reactive extractive distillation column applying the functionalized solvent silver-D2EHPA. Such a column should be operated at a solvent to feed ratio of around 5( P = 0.2 bar, T = 311 K) for 99.5% purity and 99% recovery. Under these conditions, the minimum number of equilibrium trays ( N min) to separate 1-hexene from 2-methyl-1-pentene is approximately 42, a dramatic decrease compared to N min of about 310 in the absence of silver.

Nuclear magnetic resonance and Raman studies of the aluminium complexes formed in aqueous solutions of aluminium salts containing phosphoric acid and fluoride ions

Download options Please wait... Article information DOI https://doi.org/10.1039/J19710002450 Article type Paper Download Citation J. Chem. Soc. A, 1971, 2450-2457 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Nuclear magnetic resonance and Raman studies of the aluminium complexes formed in aqueous solutions of aluminium salts containing phosphoric acid and fluoride ions J. W. Akitt, N. N. Greenwood and G. D. Lester, J. Chem. Soc. A, 1971, 2450 DOI: 10.1039/J19710002450 To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author J. W. Akitt N. N. Greenwood G. D. Lester