RASS-Enabled S/P−C and S−N Bond Formation for DEL Synthesis

DNA encoded libraries (DEL) have shown promise as a valuable technology for democratizing the hit discovery process. Although DEL provides relatively inexpensive access to libraries of unprecedented size, their production has been hampered by the idiosyncratic needs of the encoding DNA tag relegating DEL compatible chemistry to dilute aqueous environments. Recently reversible adsorption to solid support (RASS) has been demonstrated as a promising method to expand DEL reactivity using standard organic synthesis protocols. Here we demonstrate a suite of on-DNA chemistries to incorporate medicinally relevant and C−S, C−P and N−S linkages into DELs, which are underrepresented in the canonical methods.     

Phosphasilaallenes >Si = C = P− and phosphagermaallenes >Ge = C = P−

Phosphasilaallene Tip(Ph)Si = C = PMes* (Tip = 2,4,6-triisopropylphenyl, Mes* = 2,4,6-tri-tert-butylphenyl) and phosphagermaallene Mes₂Ge = C = PMes* (Mes = 2,4,6-trimethylphenyl) have been obtained by dehalogenation of their corresponding dihalophosphametallapropenes > E(X)-C(X′) = P? by tert-butyllithium. They dimerize above ?40 °C by a cycloaddition involving two E = C double bonds or the E = C and the P = C double bonds but can be characterized at low temperature by trapping reactions and by low field shifts in ³¹P, ²⁹Si and particularly ¹³C NMR for the sp carbon atom. Owing to a small increase in the steric hindrance, phosphagermaallene Tip(t-Bu)Ge = C = PMes* can be stabilized and isolated. The Ge = C double bond undergoes nearly quantitative [2 + 1] cycloadditions with chalcogens and [2 + 2] cycloadditions with aldehydes or ketones. The surprisingly stable lithiochlorosilane R(Cl₂)Si-C(Li) = PMes* (R = 9-methylfluorenyl) behaves as a synthetic equivalent of the phosphasilaallene R(Cl)Si = C = PMes*. With two alkyl groups (t-Bu) on the germanium atom, the phosphagermaallene t-Bu₂Ge = C = PMes* is not obtained but its formal dimers 1,3-digermacyclobutanes have been isolated.     

Influence of the Flexibility of Nickel PCP-Pincer Complexes on C−H and P−C Bond Activation and Ethylene Reactivity: A Combined Experimental and Theoretical Investigation

Using a pincer platform based on a bridgehead NHC donor with functional side arms, the combined effect of increased flexibility in six-membered pyrimidine-type heterocycles compared to the more often studied five-membered imidazole, and rigidity of phosphane side arms was examined. The unique features observed include: 1) the reaction of the azolium C_sp2−H bond with [Ni(cod)₂] affording a carbanionic ligand in [NiCl(PC_sp3^HP)] ( 8 ) rather than a carbene; 2) its transformation into the NHC, hydrido complex [NiH(PC^NHCP)]PF₆ ( 9 ) upon halide abstraction; 3) ethylene insertion into the Ni−H bond of the latter and ethyl migration to the N−C−N carbon atom of the heterocycle in [Ni(PC^EtP)]PF₆ ( 10 ); and 4) an unprecedented C−P bond activation transforming the P−C^NHC−P pincer ligand of 8 in a C−C^NHC−P pincer and a terminal phosphanido ligand in [Ni(PPh₂)(CC^NHCP)] ( 15 ). The data are supported by nine crystal structure determinations and theoretical calculations provided insights into the mechanisms of these transformations, which are relevant to stoichiometric and catalytic steps of general interest.     

Rhoda-Electrocatalyzed C−H Methylation and Paired Electrocatalyzed C−H Ethylation and Propylation

The use of electricity over traditional stoichiometric oxidants is a promising strategy for sustainable molecular assembly. Herein, we describe the rhoda-electrocatalyzed C−H activation/alkylation of several N-heteroarenes. This catalytic approach has been successfully applied to several arenes, including biologically relevant purines, diazepam, and amino acids. The versatile C−H alkylation featured water as a co-solvent and user-friendly trifluoroborates as alkylating agents. Finally, the rhoda-electrocatalysis with unsaturated organotrifluoroborates proceeded by paired electrolysis.     

Polymers to Selectively Remove Oxidizing Anions from Non-Oxidizing Anions and NO3 − and NO2 − and NO2 − From Polluted Waters

Abstract

A copolymer of 1-phenyl-2-diethylaminoethyl-p-aminobenzoate and polyvinyl-benzyl chloride was found to have a greater capacity for NO₃ ^? and NO₂ ^? than a previously reported nitron polymer but did not react as rapidly. The resin is readily regenerated with NH₄OH or NH₄Cl and is not affected by the pH of the water over the range of 4–10.

A copolymer of 1-(4′-nitrophenyl)-2-diethyl aminoethyl-p-nitrobenzoate and polyvinylbenzyl chloride was found to react nearly as fast as the nitron polymer and have a larger capacity for NO₃ ^? and NO₂ ^?.     

Transition Metal-Free Aromatic C−H,C−N,C−S and C−O Borylation

Aromatic organoboron compounds are highly valuable building blocks in organic chemistry. They were mainly synthesized through aromatic C−H and C−Het borylation, in which transition metal-catalysis dominate. In the past decade, with increasing attention to sustainable chemistry, numerous transition metal-free C−H and C−Het borylation transformations have been developed and emerged as efficient methods towards the synthesis of aromatic organoboron compounds. This account mainly focuses on recent advances in transition metal-free aromatic C−H, C−N, C−S, and C−O borylation transformations and provides insights to where further developments are required.     

Fluorinated Mono and Spirocyclic Δ5[sgrave]5P and Δ5[sgrave]6P Derivatives of (HO)3−nHnPO (n= 0−3)

Abstract

The properties of PF₅, HPF₄, H₂PF₃, and H₃PF₂ (Δ⁵[sgrave]⁵P derivatives of (HO)₃PO, (HO)₂HPO, (HO)H₂PO, and of the hypothetic H₃PO) and the formation of the related Δ⁵[sgrave]⁶P anions PF₆ ^–, HPF₅ ^–, and trans-H₂PF₄ ^– have been studied some years ago ^1–4. The mono and spirocyclic dioxa and tetraoxa analogues, 1 and 2 available from the corresponding precursor phosphoranes by fluoride addition could be found also as products in the reaction of phosphite 3⁵ and K⁺(CF₃)₂CFO^– together with two other phosphates, 4 and 5. A ¹⁹F–¹⁹F homocorrelated 2 D NMR spectrum of 2 indicated coupling of the P–F fluorine nuclei with two CF₃ groups by a non bond mechanism.     

Separation and preconcentration of131I− and131IO 3 − in a liquid-liquid system

The application of isotope exchange in a liquid-liquid system for the separation and preconcentration of¹³¹I^– and¹³¹IO^3/– from water is described. For this purpose a solution of elemental iodine in tri-n-butyl phosphate diluted with toluene was used. The influence of various factors on the separation efficiency of¹³¹I was investigated. These are: time of the exchange, concentration of a carrier in the aqueous phase, concentration of I₂ in the organic phase, volume ratio of the phases, pH, foreign ions, storage of the organic phase, etc. The method is quite rapid and the selective preconcentration of these chemical forms of radioiodine from water can be accomplished even in the presence of the most important fission products. This method makes also possible to separate these chemical forms from each other under controlled pH conditions. The activity of the separated radioiodine can be measured advantageously, e.g., by homogeneous liquid scintillation counting after decolourization of the organic phase.     

Ph3P+CF2CO2− as an F− and :CF2 source for trifluoromethylthiolation of alkyl halides

Trifluoromethylthiolation of alkyl halides using Ph₃P⁺CF₂CO₂^- as a fluoride and difluorocarbene source is described. Even though the process involved a cleavage of a C-F bond and the formation of R-S, S C and C-F bonds, the reactions occurred rapidly and were completed within 10 min.     

Asymmetric Synthesis of Chiral-at-P Alkenylphosphonamidates through Nickel-Catalyzed C−P Coupling of Phosphoramidites and Alkenyl Halides

P-stereogenic compounds are widely used as ligands in asymmetric catalysis and are present in a myriad of bioactive compounds and pharmaceuticals. Yet, their stereocontrolled preparation remains challenging. Herein, we report a novel strategy towards versatile chiral-at-P alkenylphosphonamidates through a one-pot Ni-catalyzed C−P coupling/diastereoselective hydrolysis of readily available phosphoramidites and alkenyl halides. Remarkably, a chemo- and diastereodivergent behavior was observed upon subtle changes in the reaction conditions. Additionally, selective derivatizations of chiral alkenylphosphonamidates demonstrate their versatility as building blocks for the synthesis of structurally diverse P-stereogenic compounds.     

The Cl−NH3, Cl−H2O,F−NH3 and F−H2O clusters and their photoelectron spectra

The geometries of the Cl^–NH₃, Cl^–H₂O, F^–NH₃ and F^–H₂O clusters are optimized using the coupled cluster method. The four lowest ionization potentials are then calculated, leading to the ground and low excited states of the neutral species. The first three IPs describe ionization from the externalp state of the halogen atom, whereas the fourth corresponds to ionization from the NH₃ or H₂O moiety, leading to charge transfer complexes. These complexes were recently observed in the photoelectron spectrum of Cl^–NH₃, in full accord with our calculations.Supported in part by the U.S.-Israel Binational Science Foundation     

Chromatography of Anions on Alumina Thin Layers: Effect of Transition Metals on CI−-Br−-I− and No− 2-NO− 3 Separations

Abstract

Chromatographic behaviour of eighteen anions on thin layers of alumina and alumina mixed with silica gel (1:1, 1:2 and 2:1) has been studied using mixed acidic organic solvent systems containing formic acid. Though the addition of silica gel to alumina enhances the mobility and clarity of detection of anions, but it causes the increased tailing for Fe(CN)^3- ₆, Cr0₄ ^2- and Cr₂O₄ ^2-. Formic acid is responsible for the differential migration of anions. All the anions remained at the starting line (R_F = 0) in pure organic solvents. Formic acid-Ketone systems gave better results compared to formic acid-alcohol systems. Development time increases with the increase of viscosity/mol. wt. of organic solvents. The mutual separation of C1, Br^?, Br^?, I^? and NO^? ₂ and NO^? ₃ were achieved on pure alumina using formic acid-acetone solvent systems. The effect of transition metals (Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) on C1^?-Br^?-I^? and NO^? ₂-NO^? ₃ separations has been studied.     

Vibrational Predissociation Spectra of C2N− and C3N−: Bending and Stretching Vibrations

We present infrared predissociation spectra of C₂N⁻(H₂) and C ₃N⁻(H₂) in the 300–1850 cm⁻¹ range. Measurements were performed using the FELion cryogenic ion trap end user station at the Free Electron Lasers for Infrared eXperiments (FELIX) laboratory. For C₂N⁻(H₂), we detected the CCN bending and CC−N stretching vibrations. For the C₃N⁻(H₂) system, we detected the CCN bending, the CC−CN stretching, and multiple overtones and/or combination bands. The assignment and interpretation of the presented experimental spectra is validated by calculations of anharmonic spectra within the vibrational configuration interaction (VCI) approach, based on potential energy surfaces calculated at explicitly correlated coupled cluster theory (CCSD(T)-F12/cc-pVTZ−F12). The H₂ tag acts as an innocent spectator, not significantly affecting the C_2,3N⁻ bending and stretching mode positions. The recorded infrared predissociation spectra can thus be used as a proxy for the vibrational spectra of the bare anions.     

Hydrothermal processing and characterization of Ce1−xPbxO2−δ solid solutions

Nanocrystals of Ce_1?xPb_xO_2?δ (x = 0.00, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, and 0.35) were prepared by a hydrothermal reaction route. During the formation reaction, buffer solutions were explored as an effective additive to retain the initial molar ratio. With increasing the Pb²⁺ content, the average crystallite size was slightly retarded. Morphologies observed by transmission electron microscope indicated that the particles were spherical-like and highly uniformed. Pb²⁺ ions are homogenously distributed in the solid solutions. Analyses using X-ray diffraction, Raman and UV spectroscopies showed that the solid solubility limit of Pb²⁺ in CeO₂ was about x = 0.20. For x < 0.20, with increasing the Pb²⁺ content, the bulk conductivity increased, and the oxygen storage capacity was enhanced as followed by a decrease in reduction temperature.     

Fortion and Reactions of Phosphonium Inner Salt, ≡ P+ C6H4O −p

Abstract

Thermolysis and reactions of methyltris(p-methoxyphenyl)phosphonium iodide with triphenylphosphine are reported. NMR and mass spectr evidence for the formation of phosphonium inner salts, →P₆,H₆ O^?-p, is presented.     

Relativistic calculations of AuSi+ and AuSi−

Theoretical calculations of the electronic structure of the ground state and a series of excited states of the AuSi⁺ and AuSi⁻ molecules are presented. The calculations were carried out with the spin-free relativistic infinite-order two-component (IOTC) method and high-level complete active space self-consistent field/complete active space perturbation theory correlated methods. The spin-orbit (SO) coupling was introduced via the restricted active space state interaction method with the use of the atomic mean-field SO integrals. The work presents the spectroscopic parameters of calculated states and full potential energy curves of the ionic AuSi⁺ and AuSi⁻ structures for the first time. Electrostatic potential maps projected on the electron density surface illustrate the significant relativistic effects on going from nonrelativistic to scalar relativistic treatments.     

Intermolecular Carbophosphination of Alkynes with Phosphole Oxides via Ni−Al Bimetal-Catalyzed C−P Bond Activation

Intermolecular carbophosphination reaction of alkynes or alkenes with unreactive C−P bonds remains an elusive challenge. Herein, we used a Ni−Al bimetallic catalyst to realize an intermolecular carbophosphination reaction of alkynes with 5-membered phosphole oxides, providing a series of 7-membered phosphepines in up to 94 % yield.     

Metal−Organic Precursors for Transition-Metal-Doped Ni2P via Pyrolysis for Efficient Overall Water Splitting and Supercapacitance

The synthesis of solvent-less bare-surface nickel phosphides is desired, considering their superior electrocatalytic properties and straightforward synthetic protocols compared to their analogues prepared from colloidal routes. Herein, we report the synthesis of [Ni{S₂P(OH)(4-CH₃OC₆H₄)}₂] (1), [Fe{S₂P(OH)(4-CH₃OC₆H₄)}₃] (2) and [Co{S₂P(OC₄H₉)(4-CH₃OC₆H₄)}₃] (3) and their utilization to form Ni₂P, Fe-Ni₂P and Co-Ni₂P in a solvent-less pyrolysis method. This solvent-free protocol involved the decomposition of complex ( 1 ) and the composites of complex ( 1 ) with ( 2 ) or ( 3 ) in the presence of triphenylphosphine (TPP) at 400 °C for one hour. The solvent-less decomposition of complex ( 1 ) without TPP formed nickel sulfide. A plausible explanation for this rare fabrication of pristine and doped Ni₂P in the absence of any solvent is suggested. All the transition metal doped phosphides improved the HER performance of pristine Ni₂P, with the 5 % Fe doped Ni₂P having the best performance, requiring 137 mV to reach a current density of 10 mA/cm². Similarly, the OER performance of un-doped Ni₂P was improved by all the doped Ni₂P catalysts, where 10 % Fe-doped Ni₂P showed the best performance requiring 326 mV to reach a current density of 10 mA/cm². Transition metal doping was also shown to improve the reaction kinetics, stability and durability of the solvent-free prepared Ni₂P.     

Synthesis,structure, and properties of randomly mixed and layer-ordered SrMn1−xGaxO3−δ perovskites

We report the synthesis of SrMn_1−xGa_xO_3−δ perovskite compounds and describe the dependence of their phase stability and structural and physical properties over extended cation and oxygen composition ranges. Using special synthesis techniques, we have extended the solubility limit of Ga³⁺ in the cubic perovskite phase to x≈0.33. Higher Ga concentrations lead to mixed phases until a single-phase ordered double-perovskite structure is obtained at x=0.5, i.e., Sr₂MnGaO_6−δ. In the cubic perovskite phase the maximum oxygen content is 3−x/2, which corresponds to 100% Mn⁴⁺. All maximally oxygenated solid solution compounds are found to order antiferromagnetically, with the transition temperature linearly decreasing as Ga content increases. Reducing the oxygen content introduces frustration into the magnetic system and a spin-glass state is observed for SrMn_0.7Ga_0.3O_2.5 below 30 K. The brownmillerite phase at low oxygen content, Sr₂MnGaO₅, is found to have Icmm crystallographic symmetry. At 12 K its magnetic structure is found to order in the Icm′m′ magnetic symmetry corresponding to a G-type antiferromagnetic structure of Mn³⁺ ions. At higher oxygen content, Sr₂MnGaO_5.5 is found to have Cmmm crystallographic symmetry with disordered oxygen vacancies. At 12 K two competing long-range magnetic structures are found for the Mn⁴⁺ sublattice having C_Im′m′m symmetry (G-type), and C_Pm′m′m symmetry (C-type), together with a G-type short-range magnetic correlations.