CO Reductive Oligomerization by a Divalent Thulium Complex and CO2-Induced Functionalization

To date, only a very limited number of complexes based on low-valent main group or f-block elements have allowed the reductive coupling of CO molecules to afford multicarbon oxygenates. Herein, we described the reactivity of the divalent thulium complex [Tm(Cpttt)2] (Cpttt = 1,2,4-tris(tert-butyl)cyclopentadienyl) towards CO, leading to selective CO reductive dimerization and trimerization into ethynediolate (C2) and ketenecarboxylate (C3) complexes, respectively. Quantum chemical (DFT) calculations were performed to shed light on the elementary steps of CO homologation and support a stepwise chain growth from the C2 to the C3 product upon addition of extra CO. The attempted decoordination of the ethynediolate frag-ment by treatment with Me3SiI led to dimerization and rearrangement into a 3,4-dihydroxyfuran-2-one complex. Investiga-tion of the reactivity of the C2 and C3 complexes towards other electrophiles led to unusual functionalization reactions: while the reaction of the ketenecarboxylate C3 complex with electrophiles yielded new multicarbon oxygenated complexes, the addition of CO2 to the ethynediolate C2 complex resulted in the formation of a very reactive intermediate, allowing C–H activation of the toluene solvent. This original intermolecular reactivity corresponds to an unprecedented functionalization of CO-derived ligands, which is induced by CO2.

Corrosion inhibition of locally de-passivated surfaces by DFT study of 2-mercaptobenzothiazole on copper

Investigating the interaction of organic inhibitors with metal and alloy surfaces is crucial for an atomic-scale understanding of their protection efficiency, particularly on the initiation of localized corrosion by pitting. Quantum chemical DFT calculations were performed to optimize the constructed model of a depassivated copper surface and to study the adsorption of 2-mercaptobenzothiazole (MBT), on different zones exposed by local depassivation. Reactive sites exist at the metal surface, at the oxide surface, as well as on the oxide edges and oxide walls. The surface-reactive sites are the unsaturated and saturated copper atoms and singly and doubly unsaturated oxygen atoms of the oxide, and the copper atoms of the metal. The sulfur (Sexo and Sendo) and nitrogen (N or NH) atoms are the reactive sites in the molecules. MBT can covalently bond to the oxide surface as well as to the oxide edges, oxide walls, and metal surface exposed by depassivation. For the thione species, local adsorption strength decreases as oxide edges > oxide surface > metal surface > oxide walls, suggesting that MBT heals the low coordinated sites. For the thiolate species, adsorption strength is similar on the different area, except the oxide walls. The results show the ability of the inhibitor to interact on different zones of a locally depassivated surface and to form a strongly adsorbed organic film, which can block the initiation of localized corrosion by enhancing the interfacial barrier properties, including in the local surface areas incompletely passivated or locally damaged by depassivation.

Unusual Para-Substituent Effects on the Intramolecular Hydrogen Bond in Hydrazone-Based Switches: Insights from Chemical Landscape Analysis and DFT Calculations

Тhe adequacy of chemical property predictions strongly depends on the structure representation, including the proper treatment of the tautomeric and isomeric forms. A combination of an in-house developed open-source tool for automatic generation of tautomers, Ambit-Tautomer, based on H-atom shift rules and standard quantum chemical (DFT) calculations is used for a detailed investigation of the possible geometric isomers, conformers and tautomers of unsubstituted and para-substituted phenylhydrazones, systems with experimentally observed unusual para-substituent effects on the intramolecular hydrogen bond (IMHB) for E-isomers of the compounds. The computational results show that the energetically preferred E-isomers are characterized by stronger IMHBs than the corresponding Z-isomers. The HN–N=C–C=N molecular fragment in the E-configurations is less sensitive to the substitution effect than the HN–N=C–C=O fragment in the isomers with Z-configuration. A probable reason for this decreased sensitivity of E-isomers to phenyl ring substitution is the more efficient conjugation and charge distribution in the HN–N=C–C=N fragment.

New Photochromic α-Methylchalcones Are Highly Photostable, Even under Singlet Oxygen Conditions: Breaking the α-Methyl Michael-System Reactivity by Reversible Peroxybiradical Formation

The α-methylated chalcones 7a–7e behave as P-type photochromic substances with photo-stationary states (PSS) as high as 15:85 when irradiated at 350 nm. These compounds are easily accessible in pure E-configuration by aldol condensation or by oxidative coupling/elimination. The α-methyl groups make these compounds potentially reactive with singlet oxygen following the gem-rule that predicts 1O2 regioselectivity. Even after long irradiations times in the presence of the singlet oxygen sensitizer tetraphenylporphyrin (TPP) and oxygen, however, no oxygenation products were detected. Under these conditions, all substrates were converted into 9:1 E/Z-mixtures despite the use of low-energy light that does not allow direct or sensitized excitation of the substrates 7. Additionally, chalcone 7a reduced the singlet oxygen reactivity of the tiglic ketone 3a by about a factor of two, indicating substantial physical quenching of singlet oxygen by the α-methylated chalcones 7a–7e. Thus, a singlet oxygen-induced E/Z-isomerization involving 1,2-dioxatetra-methylene biradicals that leads to triplet oxygen and thermodynamic E/Z-mixtures is postulated and supported by quantum chemical (DFT)-calculations.

Synthesis, characterization, structural exploration and quantum chemical calculations of (E)-8-(1-((4-aminobenzyl)imino)ethyl)-7-hydroxy-4-methyl-coumarin

Coumarin derivatives are one of the very important compounds of high biological interest. A novel coumarin derivative (E)-8-(1-((4-aminobenzyl)imino)ethyl)-7-hydroxy-4-methyl-coumarin was synthesized using substituted acetyl coumarin and 4-aminobenzylamine. Following the detailed spectroscopic characterization, the structure of the compound was confirmed using XRD studies. The novel coumarin derivative crystallizes in monoclinic crystal system in P21/c space group and displays diverse intermolecular interactions. One-dimensional array along b-axis and R_2^2 (18) supramolecular architectures are”0 formed mediated by N24—H24…O1 and C17—H17…O10 hydrogen bonds respectively. Hirshfeld surface analysis quantified that H…H, C…H and O…H contacts are the major contributors to the crystal structure with a contribution of 42.9%, 32.7% and 20.1% of total interactions respectively. Further, structural optimization was carried out using quantum chemical DFT calculations that displayed high correlation with XRD structure. The electronic absorption spectrum from TDDFT calculations is matching well with the results of UV-visible spectrum.

Influence of Amylose Size on the Structure and NMR Spectrum of Amylose-Palmitic Acid Complexes. Insight from Classical Molecular Dynamics Simulations and DFT Quantum Chemical Computations.

<p>We present, first, structural analysis of small sized amyloses complexed to palmitic acid studied using classical molecular dynamics. We show that even if amylose with a minimum of 11 residues exhibits transitional appearance of a V-type structure, 15 glucoses residues are necessary for the amylose to fold around the palmitic acid in a well-established helix conformation. Second, simulating ¹³C NMR spectrum using a strategy that combines molecular dynamics and quantum chemical DFT calculations, we demonstrate that part of the NMR spectrum is affected by the amylose size and by the presence of specific intramolecular hydrogen bonds. By mean of deconvolution procedure of NMR spectra of a 19-residues amylose calculated using a series of structures extracted from molecular dynamics, we have been able to precise the attribution of each characteristic resonances. In this context, we postulate that one chemical shift that is usually attributed to a specific carbon can, also, correspond to the presence of two different local conformations of amylose.</p>

Influence of Amylose Size on the Structure and NMR Spectrum of Amylose-Palmitic Acid Complexes. Insight from Classical Molecular Dynamics Simulations and DFT Quantum Chemical Computations.

<p>We present, first, structural analysis of small sized amyloses complexed to palmitic acid studied using classical molecular dynamics. We show that even if amylose with a minimum of 11 residues exhibits transitional appearance of a V-type structure, 15 glucoses residues are necessary for the amylose to fold around the palmitic acid in a well-established helix conformation. Second, simulating ¹³C NMR spectrum using a strategy that combines molecular dynamics and quantum chemical DFT calculations, we demonstrate that part of the NMR spectrum is affected by the amylose size and by the presence of specific intramolecular hydrogen bonds. By mean of deconvolution procedure of NMR spectra of a 19-residues amylose calculated using a series of structures extracted from molecular dynamics, we have been able to precise the attribution of each characteristic resonances. In this context, we postulate that one chemical shift that is usually attributed to a specific carbon can, also, correspond to the presence of two different local conformations of amylose.</p>