Wavelength-dependent rearrangements of an α-dione chromophore: a chemical pearl in a bis(hypersilyl) oyster.

The symmetric bissilyl-dione 3 reveals two well-separated n → π* absorption bands at = 637 nm ( = 140 mol dm cm) and 317 nm ( = 2460 mol dm cm). Whereas excitation of 3 at = 360/365 nm affords an isolable siloxyketene 4 in excellent yields, irradiation at = 590/630 nm leads to the stereo-selective and quantitative formation of the siloxyrane 5. These remarkable wavelength-dependent rearrangements are based on the electronic and steric properties provided by the hypersilyl groups.

Diastereoselective Dearomatizing Cyclizations of 5-Arylpentan-2-ones by Samarium Diiodide - A Computational Analysis.

This study analyzes the samarium diiodide-promoted cyclizations of 5-arylpentan-2-ones to dearomatized bicyclic products utilizing density functional theory. The reaction involves a single electron transfer to the carbonyl group, which occurs synchronously with the rate determining cyclization event, and a second subsequent proton-coupled electron transfer. These redox reactions are accurately computed employing small core pseudo potentials explicitly involving all f-electrons of samarium.

Symmetrical and Mixed Tris(acyl)phosphines: Synthesis, Oxidation and Photochemistry.

Invited for the cover of this issue are the groups of M. Haas, G. Gescheidt and H.

Symmetrical and Mixed Tris(acyl)phosphines: Synthesis, Oxidation and Photochemistry.

Herein, we present a convenient synthesis for symmetrical and mixed substituted tris(acyl)phosphines (TAPs) starting from red phosphorus. All TAPs exhibit a phosphaalkene-acylphosphine equilibrium, which was investigated in detail by variable-temperature (VT) NMR spectroscopy supported by density-functional theory (DFT) calculations. Depending on the substituents, two phosphaalkene derivatives and ten acylphosphine derivatives could be isolated.

Fabrication of Amorphous Silicon-Carbon Hybrid Films Using Single-Source Precursors.

The aim of this study was the preparation of different amorphous silicon-carbon hybrid thin-layer materials according to the liquid phase deposition (LPD) process using single-source precursors. In our study, 2-methyl-2-silyltrisilane (methylisotetrasilane; ), 1,1,1-trimethyl-2,2-disilyltrisilane (trimethylsilylisotetrasilane; ), 2-phenyl-2-silyltrisilane (phenylisotetrasilane; ), and 1,1,2,2,4,4,5,5-octamethyl-3,3,6,6-tetrasilylcyclohexasilane (cyclohexasilane; ) were utilized as precursor materials and compared with the parent compound 2,2-disilyltrisilane (neopentasilane; ). Compounds - were successfully oligomerized at λ = 365 nm with catalytic amounts of the neopentasilane oligomer ().

To Isomerize or not to Isomerize? E/Z Isomers of Cyclic Azobenzene Derivatives and Their Reactivity Upon One-Electron Reduction.

Azo compounds are efficient electron acceptors. Upon one-electron reduction they generally isomerize forming the thermodynamically most stable radical anion. Herein we show that the size of the central ring in 1,2-diazocines and diazonines has a ruling influence on the configuration of the one-electron reduced species.

Samarium Diiodide Acting on Acetone-Modeling Single Electron Transfer Energetics in Solution.

Samarium diiodide is a versatile single electron transfer (SET) agent with various applications in organic chemistry. Lewis structures regularly insinuate the existence of a ketyl radical when samarium diiodide binds a carbonyl group. The study presented here investigates this electron transfer by the means of computational chemistry.

An NHC-Mediated Metal-Free Approach towards an NHC-Coordinated Endocyclic Disilene.

A convenient metal-free approach towards an N-heterocyclic carbene (NHC)-coordinated disilene 2 is described. Compound 2, featuring the disilene incorporated in cyclopolysilane framework, was obtained in good yield and characterized using NMR spectroscopy and X-ray crystallography. Density functional theory (DFT) calculations of the reaction mechanism provide a rationale for the observed reactivity and give detailed information on the bonding situation of the base-stabilized disilene.

Correction: Synthesis and characterization of diacylgermanes: persistent derivatives with superior photoreactivity.

Correction for 'Synthesis and characterization of diacylgermanes: persistent derivatives with superior photoreactivity' by Sabrina D. Püschmann , , 2021, , 11965-11974, DOI: 10.1039/D1DT02091A.

Isolable Geminal Bisgermenolates: A New Synthon in Organometallic Chemistry.

We have synthesized the first isolable geminal bisenolates LKGe[(CO)R] (=2,4,6-trimethylphenyl (,), L=THF for () or [18]-crown-6 for ()), a new synthon for the synthesis of organometallic reagents. The formation of these derivatives was confirmed by NMR spectroscopy and X-ray crystallographic analysis. The UV/Vis spectra of these anions show three distinct bands, which were assigned by DFT calculations.

Isolable Geminal Bisgermenolates: A New Synthon in Organometallic Chemistry.

We have synthesized the first isolable geminal bisenolates L K Ge[(CO)R] (R=2,4,6-trimethylphenyl (2 a,b), L=THF for (2 a) or [18]-crown-6 for (2 b)), a new synthon for the synthesis of organometallic reagents. The formation of these derivatives was confirmed by NMR spectroscopy and X-ray crystallographic analysis. The UV/Vis spectra of these anions show three distinct bands, which were assigned by DFT calculations.

Synthesis and characterization of diacylgermanes: persistent derivatives with superior photoreactivity.

Acylgermanes are known as highly efficient photoinitiators. In this contribution, we present the synthesis of new diacylgermanes 4a-evia a multiple silyl abstraction methodology. The method outperforms the state-of-the-art approach (Corey-Seebach reaction) towards diacylgermanes in terms of group tolerance and toxicity of reagents.

On Complex Formation between 5-Fluorouracil and β-Cyclodextrin in Solution and in the Solid State: IR Markers and Detection of Short-Lived Complexes by Diffusion NMR.

In this work, the nuclear magnetic resonance (NMR) and IR spectroscopic markers of the complexation between 5-fluorouracil (5-FU) and β-cyclodextrin (β-CD) in solid state and in aqueous solution are investigated. In the attenuated total reflectance(ATR) spectra of 5-FU/β-CD products obtained by physical mixing, kneading and co-precipitation, we have identified the two most promising marker bands that could be used to detect complex formations: the C=O and C-F stretching bands of 5-FU that experience a blue shift by ca. 8 and 2 cm upon complexation.

The Chemistry of Acylgermanes: Triacylgermenolates Represent Valuable Building Blocks for the Synthesis of a Variety of Germanium-Based Photoinitiators.

The formation of a stable triacylgermenolate as a decisive intermediate was achieved by using three pathways. The first two methods involve the reaction of KOBu or alternatively potassium with tetraacylgermane yielding via one electron transfer. The mechanism involves the formation of radical anions (shown by EPR).

Exciton Coupling and Conformational Changes Impacting the Excited State Properties of Metal Organic Frameworks.

In recent years, the photophysical properties of crystalline metal-organic frameworks (MOFs) have become increasingly relevant for their potential application in light-emitting devices, photovoltaics, nonlinear optics and sensing. The availability of high-quality experimental data for such systems makes them ideally suited for a validation of quantum mechanical simulations, aiming at an in-depth atomistic understanding of photophysical phenomena. Here we present a computational DFT study of the absorption and emission characteristics of a Zn-based surface-anchored metal-organic framework (Zn-SURMOF-2) containing anthracenedibenzoic acid (ADB) as linker.

Conformational Analyses of Physiological Binary and Ternary Copper(II) Complexes with l-Asparagine and l-Histidine; Study of Tridentate Binding of Copper(II) in Aqueous Solution.

This study explores the structural properties and energy landscapes of the physiologically important bis(l-asparaginato)copper(II) [Cu(l-Asn)] and (l-histidinato)(l-asparaginato)copper(II) [Cu(l-His)(l-Asn)]. The conformational analyses in the gas phase and implicitly modeled water medium, and magnetic parameters of electron paramagnetic resonance spectra were attained using density functional theory calculations. The apical Cu coordination and hydrogen bonding were analyzed.

Unprecedented Bifunctional Chemistry of Bis(acyl)phosphane Oxides in Aqueous and Alcoholic Media.

Tailor-made photoinitiators play an important role for efficient radical polymerisations in aqueous media, especially in hydrogel manufacturing. Bis(acyl)phosphane oxides (BAPOs) are among the most active initiators. Herein, we show that they display a remarkable photochemistry in aqueous and alcoholic media: Photolysis of BAPOs in the presence of water or alcohols provides a new delocalized π-radical, which does not participate in the polymerization.

Anharmonicity of Vibrational Modes in Hydrogen Chloride-Water Mixtures.

A thorough analysis of molecular vibrations in the binary system hydrogen chloride/water is presented considering a set of small mixed and pure clusters. In addition to the conventional normal-mode analysis based on the diagonalization of the Hessian, anharmonic frequencies were obtained from the perturbative VPT2 and PT2-VSCF method using hybrid density functional theory. For all normal modes, potential energy curves were modeled by displacing the atoms from the minimum geometry along the normal mode vectors.

Competing Intramolecular Hydrogen Bond Strengths and Intermolecular Interactions in the 4-Aminobutanol-Water Complex.

We seek to determine the effect of competing intermolecular hydrogen bonds from water on the preferred conformation of 4-aminobutanol (4AB) monomers stabilized by intramolecular hydrogen bonds. Toward this end, the rotational spectrum of the 4-aminobutanol-HO complex was recorded using Fourier transform microwave spectroscopy and fit to the rotational, quadrupole coupling, and centrifugal distortion constants of the Watson S-reduction Hamiltonian. The experimental results are consistent with a 4AB-water complex that preserves the intramolecular hydrogen bond within the 4AB monomer and forms a single intermolecular bond with water acting as a donor.

Charge-Transfer Salts of 6,6-Dicyanopentafulvenes: From Topology to Charge Separation in Solution.

6,6-Dicyanopentafulvene derivatives and metallocenes with redox potentials appropriate for forming their radical anions form highly persistent donor-acceptor salts. The charge-transfer salts of 2,3,4,5-tetraphenyl-6,6-dicyanofulvene with cobaltocene (1⋅Cp Co) and 2,3,4,5-tetrakis(triisopropylsilyl)-6,6-dicyanofulvene with decamethylferrocene (2⋅Fc*) have been prepared. The X-ray structures of the two salts, formed as black plates, were obtained and are discussed herein.

Wavelength-Dependent Photochemical Stability of Photoinitiator-Derived Macromolecular Chain Termini.

Herein, we report the unique-and first time-wavelength-dependent investigation with strictly monochromatic light of 305-405 nm wavelength into the stability of photoinitiator-derived chain termini of poly(methyl methacrylate) using a tunable laser system fused with pulsed-laser irradiation and size exclusion chromatography hyphenated to high-resolution electrospray mass spectrometry (PLI-SEC-ESI-MS). We assess several substitution patterns of methyl groups on the common benzoyl-type radical fragment. Critically, methyl substitution in the 2- and 6-positions of the benzoyl moiety, i.

Interplay of Intermolecular and Intramolecular Hydrogen Bonds on Complex Formation: The 3-Aminopropanol-Water van der Waals Complex.

This combined experimental and theoretical study answers the question whether the intramolecular hydrogen-bond strength in amino alcohols is dependent on the ring size. For this purpose, the rotational spectrum of the 3-aminopropanol-HO van der Waals complex was recorded using Fourier-transform microwave spectroscopy and fit to the rotational, quadrupole coupling, and centrifugal distortion constants of the Watson A-reduction Hamiltonian. The experimental results are consistent with an ab initio conformation calculated at the MP2/6-311++G(d,p) level that involves the lowest energy 3-aminopropanol monomer and consists of a hydrogen bonding network.

Insights into the Hydrogen-Atom Transfer of the Blue Aroxyl.

An experimental and theoretical study on hydrogen-atom transfer dynamics in the hydrogen-bonded substituted phenol/phenoxyl complex of the blue aroxyl (2,4,6-tri-tert-butylphenoxyl) is presented. The experimental exchange dynamics is determined in different organic solvents from the temperature-dependent alternating line-width effect in the continuous-wave ESR spectrum. From bent Arrhenius plots, effective tunnelling contributions with parallel heavy-atom motion are concluded.

Infrared absorption of methanol-water clusters (CHOH)(HO), n = 1-4, recorded with the VUV-ionization/IR-depletion technique.

We recorded infrared (IR) spectra in the CH- and OH-stretching regions of size-selected clusters of methanol (M) with one water molecule (W), represented as MW, n = 1-4, in a pulsed supersonic jet using the photoionization/IR-depletion technique. Vacuum ultraviolet emission at 118 nm served as the source of ionization in a time-of-flight mass spectrometer to detect clusters MW as protonated forms MWH. The variations in intensities of MWH were monitored as the wavelength of the IR laser light was tuned across the range 2700-3800 cm.

Bis(mesitoyl)phosphinic acid: photo-triggered release of metaphosphorous acid in solution.

Bis(mesitoyl)phosphinic acid and its sodium salt display a unique photo-induced reactivity: both derivatives stepwise release two mesitoyl radicals and, remarkably, metaphosphorous acid (previously postulated as transient species in the gas phase), providing a new phosphorus-based reagent.