Catalytic ethylation of alkylbenzenes at high pressure

Study of the catalytic ethylation of p-t-butyltoluene in the presence of organosodium compounds, and of toluene in the presence of organopotassium compounds, was carried out at an ethylene pressure of 40 bar. Various yields of different products were obtained after 23 h of reaction in the presence of different tertiary polyamines used to complex and solubilize the organoalkali compounds. A higher initial ethylation rate was observed in the presence of organosodium than in the presence of organopotassium species. However, the thermal stability of organopotassium species being higher, much higher yields were observed in their presence in catalytic ethylation reactions than those observed previously. The results obtained concerning metallation or ethylation of hindered alkylaromatics may be interpreted by an anionic mechanism and the activation by a steric effect.     

An enzyme-based E-DNA sensor for sequence-specific detection of femtomolar DNA targets

In this work, we report an enzyme-based E-DNA sensor for the sequence-specific detection of nucleic acids. This DNA sensor employs a "stem-loop" DNA probe dually labeled with biotin and digoxigenin (DIG). The probe is immobilized at an avidin-modified electrode surface via the biotin-avidin bridge, and the DIG serves as an affinity tag for the enzyme binding. In the initial state of the sensor, the probe adopts the stem-loop structure, which shields DIG from being approached by a bulky horseradish peroxidase-linked-anti-DIG antibody (anti-DIG-HRP) due to the steric effect. After hybridization, the probe undergoes a significant conformational change, forcing DIG away from the electrode. As a result, the DIG label becomes accessible by the anti-DIG-HRP, and the target hybridization event can be sensitively transduced via the enzymatically amplified electrochemical current signal. By using this new strategy, we demonstrate that the prototype E-DNA sensor has been able to detect as low as femtomolar DNA targets with excellent differentiation ability for even single mismatches.     

Front Cover: A Tetrapodal Penta-Carbene Ligand and Iron(III) Complex (Eur. J. Inorg. Chem. 20/2023)

We report the first tetrapodal pentadentate ligand composed of five N-heterocyclic carbene donors. The proto-ligand [CC_4H5^Me](OTf)₃ (3) is formed in good yields from commercially available reagents. Upon removal of 5 proton equivalents from 3 with bulky non-nucleophilic bases a dianionic penta-carbene framework is provided in good yields as a dilithium complex CC₄^MeLi₂ ( 4 ). Addition of FeCl₃ to a solution of 4 formed in situ provides CC₄^MeFeCl ( 5 ) in moderate yield. Solution-state magnetism measurements of 5 are consistent with a S=1/2 Fe(III) center. The related diamagnetic Fe(II) compound CC₄^MeFe ( 6 ) can be formed through reduction of 5 using KC₈ though poor solubility characteristics have hampered its formation on a preparative scale and full characterization.     

The polyoctahedral silsesquioxane (POSS) 1,3,5,7,9,11,13,15‐octaphenylpentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane (octaphenyl‐POSS)

Solvent‐free single crystals of 1,3,5,7,9,11,13,15‐octaphenylpentacyclo[9.5.1.1^3,9.1^5,15.1^7,13]octasiloxane (abbreviated as octaphenyl‐POSS), C₄₈H₄₀O₁₂Si₈, were obtained by dehydration/condensation of the tetrol Si₄O₄(Ph)₄(OH)₄. The powder pattern generated from the single‐crystal data matches well with the experimentally measured powder pattern of commercial octaphenyl‐POSS. The geometry of the centrosymmetric molecule in the crystal was compared with that in the gas phase, and had shorter Si—O bond lengths and a broader range of Si—O—Si bond angles. The average Si—O bond length [1.621 (3) Å], and Si—O—Si and O—Si—O bond angles [149 (5) and 109 (1)°, respectively] were within the same range measured previously for octaphenyl‐POSS solvates.     

Fredholmness of Linear Combinations of Two Idempotents

Let E and F be idempotent operators on a complex Hilbert space, and let a and b be nonzero scalars with a + b ≠ 0. We prove that aE + bF is Fredholm if and only if E + F is, thus answering affirmatively a question asked by Koliha and Rakočević.      

Self-Consistent Solutions for the Scattering State with Two Free Electrons

Wave functions for the scattering states with two free electrons in the field of an ion core are explicitly calculated by the self-consistent, continuum Hartree–Fock (CHF) theory. Typically, such states are associated with the three-body recombination, collisional ionization and photo-double ionization, but have never been directly studied previously. The calculated continuum orbitals are found to be predominantly of the plane-wave forms, as though the system is translation invariant, in the context of many-body HF theory. The symmetry is mildly broken by the presence of the core ion, at about fifteen-percents level, indicating that the orbitals are largely delocalized and the effect of the core potential is an important but minor perturbation. The properties of channel orthogonality and completeness are preserved by the nearly plane wave forms. To test the validity of this finding and the CHF, the continuum orbitals are used to evaluate the amplitudes for the electron impact ionization, and the amputation procedure, that is crucial in the theory, is also critically re-examined.     

Palladium-catalyzed coupling reactions of (ArCH2)Ti(O-i-Pr)3 with aromatic or heteroaromatic bromides

Three benzyltitanium compounds of (ArCH₂)Ti(O-i-Pr)₃ (Ar = Ph (1a), 4-MeOC₆H₄ (1b), 4-FC₆H₄ (1c)) were prepared and used as benzyl nucleophiles for coupling reactions with aromatic or heteroaromatic bromides. The simple catalytic system of 1 mol % Pd(OAc)₂ and 2 mol % PCy₃ worked efficiently for a wide variety of aromatic bromides, producing diarylmethanes in good to excellent yields of up to 96%. Coupling reactions of hindered aromatic bromides or aromatic bromides containing electron-withdrawing substituents were slower over longer reaction times of 3–6 h. Reactions of heteroaromatic bromides of bromopyridines, bromofurans, or bromothiophenes with benzyl reagents of 1a or 1b required either longer reaction times of 12–24 h or a higher reaction temperature of 80 °C, producing pyridyl-, furyl-, and thienyl-arylmethanes in moderate yields.