Metal-cation-mediated hydrolysis of phosphonoformate diesters: chemoselectivity and catalysis(1)

Switching between P-acylation and O-acylation of H-phosphonates with chloroformates by changing acyl pyridinium and acyl ammonium ions in a microflow reactor

We report the first switchable acylation of H-phosphonate with chloroformate. The acylation site (P vs. O) in H-phosphonate was switched by changing the acyl pyridinium/ammonium ions. Unexpected phosphite formation was observed during the O-acylation of H-phosphonate. Twenty-six structurally diverse phosphotriesters and phosphonoformate esters were synthesized in microflow reactors.

The Hydrolysis of Phosphinates and Phosphonates: A Review

Phosphinic and phosphonic acids are useful intermediates and biologically active compounds which may be prepared from their esters, phosphinates and phosphonates, respectively, by hydrolysis or dealkylation. The hydrolysis may take place both under acidic and basic conditions, but the C-O bond may also be cleaved by trimethylsilyl halides. The hydrolysis of P-esters is a challenging task because, in most cases, the optimized reaction conditions have not yet been explored. Despite the importance of the hydrolysis of P-esters, this field has not yet been fully surveyed. In order to fill this gap, examples of acidic and alkaline hydrolysis, as well as the dealkylation of phosphinates and phosphonates, are summarized in this review.

Catalytic Degradation of Nerve Agents

Nerve agents (NAs) are a group of highly toxic organophosphorus compounds developed before World War II. They are related to organophosphorus pesticides, although they have much higher human acute toxicity than commonly used pesticides. After the detection of the presence of NAs, the critical step is the fast decontamination of the environment in order to avoid the lethal effect of these organophosphorus compounds on exposed humans. This review collects the catalytic degradation reactions of NAs, in particular focusing our attention on chemical hydrolysis. These reactions are catalyzed by different catalyst categories (metal-based, polymeric, heterogeneous, enzymatic and MOFs), all of them described in this review.

The chemistry of Ce-based metal-organic frameworks

Metal-organic frameworks (MOFs) have gained widespread attention due to their modular construction that allows the tuning of their properties. Within this vast class of compounds, metal carboxylates containing tri- and tetravalent metal ions have been in the focus of many studies due to their often high thermal and chemical stabilities. Cerium has a rich chemistry, which depends strongly on its oxidation state. Ce(iii) exhibits properties typically observed for rare earth elements, while Ce(iv) is mostly known for its oxidation behaviour. In MOF chemistry this is reflected in their unique optical and catalytic properties. The synthetic parameters for Ce(iii)- and Ce(iv)-MOFs also differ substantially and conditions must be chosen to prevent reduction of Ce(iv) for the formation of the latter. Ce(iii)-MOFs are usually reported in comprehensive studies together with those constructed with other RE elements and normally they are isostructural. They exhibit a greater structural diversity, which is reflected in the larger variety of inorganic building units. In contrast, the synthesis conditions of Ce(iv)-MOFs were only recently (2015) established. These lead selectively to hexanuclear Ce-O clusters that are well-known for Zr-MOFs and therefore very similar structural and isoreticluar chemistry is found. Hence Ce(iv)-MOFs exhibit often high porosity, while only a few porous Ce(iii)-MOFs have been described. Some of these show structural flexibility which makes them interesting for separation processes. For Ce(iv)-MOFs the redox properties are most relevant. Thus, they are intensively discussed for catalytic, photocatalytic and sensing applications. In this perspective, the synthesis, structural chemistry and properties of Ce-MOFs are summarized.

Phosphonic acid: preparation and applications

The phosphonic acid functional group, which is characterized by a phosphorus atom bonded to three oxygen atoms (two hydroxy groups and one P=O double bond) and one carbon atom, is employed for many applications due to its structural analogy with the phosphate moiety or to its coordination or supramolecular properties. Phosphonic acids were used for their bioactive properties (drug, pro-drug), for bone targeting, for the design of supramolecular or hybrid materials, for the functionalization of surfaces, for analytical purposes, for medical imaging or as phosphoantigen. These applications are covering a large panel of research fields including chemistry, biology and physics thus making the synthesis of phosphonic acids a determinant question for numerous research projects. This review gives, first, an overview of the different fields of application of phosphonic acids that are illustrated with studies mainly selected over the last 20 years. Further, this review reports the different methods that can be used for the synthesis of phosphonic acids from dialkyl or diaryl phosphonate, from dichlorophosphine or dichlorophosphine oxide, from phosphonodiamide, or by oxidation of phosphinic acid. Direct methods that make use of phosphorous acid (H3PO3) and that produce a phosphonic acid functional group simultaneously to the formation of the P-C bond, are also surveyed. Among all these methods, the dealkylation of dialkyl phosphonates under either acidic conditions (HCl) or using the McKenna procedure (a two-step reaction that makes use of bromotrimethylsilane followed by methanolysis) constitute the best methods to prepare phosphonic acids.

Lanthanide-mediated phosphoester hydrolysis and phosphate elimination from phosphopeptides

Lanthanide ions can mediate both phosphomonoester hydrolysis and beta-elimination of inorganic phosphate from polypeptide substrates under near-physiological conditions of pH, temperature, and salt.

Nucleophilic dephosphorylation of p-nitrophenyl diphenyl phosphate in cationic micellar media

The kinetics of nucleophilic dephosphorylation of p-nitrophenyl diphenyl phosphate by hydroxamate ions (R'(C=O)N(RO-)) have been investigated in aqueous cationic micellar media at pH 9.12 and 27 degrees C. The pseudo-first-order rate constant-surfactant profiles show micelle-assisted bimolecular reactions involving interfacial ion exchange between bulk aqueous media and micellar pseudophase. N-Substituted hydroxamate ion shows higher reactivity over the unsubstituted hydroxamate ions in cationic micellar media. The kinetic data are discussed in terms of the pseudophase ion exchange model.

Kinetics of phosphodiester cleavage by differently generated cerium(iv) hydroxo species in neutral solutions

Neutral aqueous solutions of cerium ammonium nitrate obtained by dilution of their acetonitrile stock solution with imidazole buffer show high catalytic activity in the hydrolysis of bis(p-nitrophenyl) phosphate (BNPP) and better reproducibility than other similar systems, but suffer from low stability. The kinetics of catalytic hydrolysis is second-order in Ce(IV), independent of pH in the range 5-8 and tentatively involves the Ce2(OH)7+ species as the active form. Attempts to stabilize the active species by different types of added ligands failed, but the use of Ce(IV) complexes pre-synthesized in an organic solvent with potentially stabilizing ligands as precursors of active hydroxo species appeared to be more successful. Three new Ce(IV) complexes, [Ce(Phen)2O(NO3)2], [Ce(tris)O(NO3)(OH)] and [Ce(BTP)2(NO3)4].2H2O (BTP = bis-tris propane, 1,3-bis[tris(hydroxymethyl)methylamino]propane), were prepared by reacting cerium ammonium nitrate with the respective ligands in acetonitrile and were characterized by analytical and spectroscopic techniques. Aqueous solutions of these complexes undergo rapid hydrolysis producing nearly neutral polynuclear Ce(IV) oxo/hydroxo species with high catalytic activity in BNPP hydrolysis. Potentiometric titrations of the solutions obtained from the complex with BTP revealed the formation of Ce4(OH)15+ species at pH > 7, which are protonated affording Ce4(OH)14(2+) and then Ce4(OH)13(3+) on a decrease in pH from 7 to 5. The catalytic activity increases strongly on going to species with a higher positive charge. The reaction mechanism involves first- and second-order in catalyst paths as well as intermediate complex formation with the substrate for higher charged species.