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A detailed approach into electronic effects of ligands on gold‐alkyne interactions has been carried out in the gas phase using tandem mass spectrometry. A semi‐empirical method coupled to DFT calculations was used to quantify ligands effects on Au−CC bond strength. To this end, the critical energies of 16 [L−Au‐hex‐3‐yne]+ complexes with different L ligands were determined through collision induced dissociation. It was observed that electron‐rich ligands destabilize the gold‐alkyne bond, whereas phosphites and carbenes strengthened it. The influence of alkyne electronic effects on the gold‐alkyne bond has also been studied by dissociation in tandem mass spectrometry on four different alkynes. In an original approach, two successive ion‐molecule reactions within the mass spectrometer were used to measure the relative affinity of gold to an alkyne by exchange reactions. The result is that the more electron‐rich the alkyne, the stronger the gold‐alkyne bond. [ABSTRACT FROM AUTHOR]

This article describes a density functional theory (DFT) study to explore a bio‐inspired NiFe complex known for its experimental activity in electro‐reducing CO2 to CH4 when adsorbed on graphite. The coordination properties of the complex are investigated in isolated form and when physisorbed on a graphene surface. A comparative analysis of DFT approaches for surface modeling is conducted, utilizing either a finite graphene flake or a periodic carbon surface. Results reveal that the finite model effectively preserves all crucial properties. By examining predicted structures arising from CO2 insertion within the mono‐reduced NiFe species, whether isolated or adsorbed on the graphene flake, a potential species for subsequent electro‐reduction steps is proposed. Notably, the DFT study highlights two positive effects of complex adsorption: facile electron transfers between graphene and the complex, finely regulated by the complex state, and a lowering of the thermodynamic demand for CO2 insertion. [ABSTRACT FROM AUTHOR]

Pyrido[4,3,2-KI] acridines represent a new class of heterocycles and isomers of marine alkaloids. Molecular calculations were found to account for the observed regioselectivity.

Research has been conducted on the 4-pentenyl, 5-hexenyl, 6-heptenyl, and 7-octenyl fluorinated and ether radicals. The cyclization reactions of these radicals have been conducted via the hybrid Hartree-Fock density functional method and the results are discussed.

Density functional methods were used to examined alkyne-dicobalt hexacarbonyl compounds, to determine electronic differences and their role in regiochemical outcomes.

Research has been conducted on the acylation reaction regioselectivity. The results indicate that regioselectivity of the Vilsmeier-Haack reaction can be explained by the stability of the cationic intermediate resulting from the attack on C (sub)4.

The reaction of methanimine with hydrogen cyanide is reported.

A study has been conducted to examine the application of the symmetry-adapted perturbation theory to characterize the pair and non-additive interactions in water clusters. Experiments involved close scrutiny of the structures corresponding to the global minima and transition states of the trimer that govern the hydrogen bond rearrangement. Findings indicate the all of the used density functional methods fail to correctly describe the three-body interactions in the water trimer.

Unlike its shorter analog, cysteine, and its methylated derivative, methionine, homocysteine is not today a proteinogenic amino acid. However, this thiol containing amino acid is capable of forming an activated species intramolecularly. Its thiolactone could have made it an interesting molecular building block at the origin of life on Earth. Here we study the cyclization of homocysteine in water and show theoretically and experimentally that in an acidic medium the proportion of thiolactone is significant. This thiolactone easily reacts with amino acids to form dipeptides. We envision that these reactions may help interpret why a methionine residue is introduced at the start of all protein synthesis. [ABSTRACT FROM AUTHOR]

Herein, a new heterobimetallic CoFe complex is reported with the aim of comparing its performance in terms of H2 production within a series of related MFe complexes (M = Ni, Fe). The fully oxidized [(LN2S2)CoII(CO)FeIICp]+ complex (CoIIFeII, LN2S2 2− = 2,2′-(2,2′-bipyridine-6,6′-diyl)bis(1,1′-diphenylethanethiolate), Cp− = cyclopentadienyl anion) can be (electro)chemically reduced to its CoIFeII form, and both complexes have been isolated and fully characterized by means of classic spectroscopic techniques and theoretical calculations. The redox properties of CoIIFeII have been investigated in DMF, revealing that this complex is the easiest to reduce by one-electron among the analogous MFe complexes (M = Ni, Fe, Co). Nevertheless, it displays no electrocatalytic activity for H2 production, contrary to the FeFe and NiFe analogs, which have proven remarkable performance. [ABSTRACT FROM AUTHOR]

The mechanism of the metathesis reactions of sigma-bond of water and alcohols with palladium hydrochloride and methyl complexes was established. An additional lone pair not involved in any reaction has caused a lowering of the transition state of the orbitals secondary to the rehybridization effect of the nonreacting pair. Furthermore, the reactions were determined by the electrostatic charges of the reacting entities.

The study rationalizes for the first time the experimentally observed reactivity differences of cyclohexene, cylopentene and norbornene. The reactivity of different Co2(CO)6-acetylene complexes in the Pauson-Khand reaction is found to be strongly dependent on the nature of the olefin.

Examines the applicability of various density functional theory (DFT) methods to describe the anisotropy of the intermolecular potential energy surfaces of hydrogen-bonded and van der Waals complexes. Comparison between supermolecule coupled-cluster method and perturbational symmetry-adapted perturbation theory.

Oxetanes are key synthons for asymmetric synthesis and also effective in directing ortho‐lithiation. This work first reports the solution and the solid‐state structure of an ortho‐lithiated aryloxetane (1‐Li) in the presence/absence of a bidentate ligand such as N,N,N′,N′‐tetramethylethylenediamine (TMEDA). Single crystal X‐ray diffraction analysis of 1‐Li revealed a singular crystallographic structure in which the asymmetric unit comprises a core where the lithium atom is coordinated to the nitrogen atom of half a molecule of TMEDA and intramolecularly stabilised by the oxetane ring oxygen. This aggregation state is unprecedented in ortho‐lithiated arenes. Variable temperatures multinuclear magnetic resonance (1H, 7Li, 13C) mono‐ and two‐dimensional NMR studies and DFT computations supported the coexistence in solution of three chelated bridged dimeric aggregates, in slow equilibration at 180 K. The major isomer is an heterochiral aggregate on the basis of 1H,7Li‐HOESY and 1H,1H‐NOESY experiments. Conclusions were supported by the preparation of enantiomerically enriched (S)‐1‐Li. The privileged formation of homochiral aggregates from racemic mixtures may also have implications for the development of chiral resolution processes. [ABSTRACT FROM AUTHOR]

Presents a theoretical study of the OH[sup -]H[sub 2]O)[sub 2] system and the nature and importance of nonadditive three-body interactions. Account on the supermolecule Moller-Plesset (MP) perturbation theory; Details on the symmetry-adapted perturbation theory (SAPT); Comparison of the MP and SAPT convergence.

The description of the electric properties of the subsystems and effect of the basis set superposition error (BSSE) correction on the geometry of the full system was examined using the intermolecular interaction field. The study revealed that the BSSE was large with the diffuse basis sets that were needed for accurate polarizability and the uncorrected geometry underestimated the intermolecular distance and overestimated the length of the water OH bond involved in the H-bond.

Ligand electronic effects in gold(i) chemistry have been evaluated by means of the experimental determination of M–CO bond dissociation energies for 16 [L–Au–CO]+ complexes, bearing L ligands widely used in gold catalysis. Energy-resolved analyses have been made using tandem mass spectrometry with collision-induced dissociation. Coupled with DFT calculations, this approach enables the quantification of ligand effects based on the LAu–CO bond strength. A further energy decomposition analysis gives access to detailed insights into this bond's characteristics. Whereas small differences are observed between phosphine- and phosphite-containing gold complexes, carbene ligands are shown to stabilize the gold-carbonyl bond much more efficiently. [ABSTRACT FROM AUTHOR]

Life developed on Earth probably about 3.8 billion years ago, on a planet that was already largely covered by oceans and where the atmosphere was very humid. The reactions, which may have led to the formation of the first polymers, particularly to the first peptides and nucleic acids, must have been compatible with these conditions. This is the case of the reaction of nitriles with aminothiols, such as cysteine and homocysteine. Since aminonitriles are the probable precursors of amino acids, this condensation reaction has been able to rapidly yield dipeptides, tripeptides, oligomers and even true polymers, each containing thiol functions. These thiol-rich peptides (TRP's) would then have assumed the various catalytic roles that the peptides containing cysteine residues play today. They allowed a rapid bloom of life in the primitive ocean. In this scenario, RNA's are not the first polymers, but have been synthesized, like DNA's, thanks to the catalytic properties of thiols in a mostly TRP world. In this world, due to its ability to form a thiolactone, homocysteine may have played the leading role in enabling the previously formed oligomers to be stappled together, thus accelerating the formation of long peptide chains. [ABSTRACT FROM AUTHOR]

It has been possible to make a detailed B3LYP investigation of the regiochemistry-determining event in the Pauson-Khand reaction (PKR). It is concluded that productive axial coordination of an olefin must be taken into account in both theoretical and synthetic PKR studies.

Since methionine is capable of self-activation, the dipeptides formed by the reaction of its activated form with another amino acid were over-represented in the primitive ocean. This hypothesis gives a key role to methionine in the development of life on the Earth. It could explain why a methionine residue begins the synthesis of all proteins, while it is usually not necessary for its catalytic activity, and why the start codon is relatively variable in prokaryotes. [ABSTRACT FROM PUBLISHER]

The feasibility of the cyclization of γ-alkylthiobutyric acid derivatives to form previously unknown five-membered-ring acyl sulfonium cations was studied. Experimental results were in good agreement with our DFT calculations that predicted such cyclizations to be easy if starting with acyl iodides and mixed anhydrides of triflic acid. Particularly efficient were the reactions of γ-alkylthiobutyryl fluorides with trimethylsilyl triflate in CDCl3 solution, which led to cyclic acyl sulfonium triflates. In some cases, the observed acyl sulfonium salts were stable enough to be characterized by NMR spectroscopy. They were found to be both alkyl-transfer reagents and acylating agents. They react with amines to form amides. These findings lend some weight to our hypothesis that the acyl sulfonium derived from methionine may have played a major role in the prebiotic synthesis of the first peptides on the primitive Earth. [ABSTRACT FROM AUTHOR]

The intramolecular p-dimerization between two 4,4'-bipyridinium cation radicals directly connected to the wide rim of a calixarene is described. The ability of a phenol-containing calixarene to dimerize in its two-electron-reduced state depends on a subtle balance of weak interactions associated with hydrogen bond formation on the lower rim and orbital overlap between p-radicals on the upper rim. [ABSTRACT FROM AUTHOR]

Organozinc hydroxides, RZnOH, possessing the proton-reactive alkylzinc group and the CO2-reactive ZnOH group, represent an intriguing group of organometallic precursors for the synthesis of novel zinc carbonates. Comprehensive experimental and computational investigations on 1) solution and solid-state behavior of tBuZnOH ( 1) species in the presence of Lewis bases, namely, THF and 4-methylpyridine; 2) step-by-step sequence of the reaction between 1 and CO2; and 3) the effect of a donor ligand and/or an excess of tBu2Zn as an external proton acceptor on the reaction course are reported. DFT calculations for the insertion of carbon dioxide into the dinuclear alkylzinc hydroxide 12 are fully consistent with 1H NMR spectroscopy studies and indicate that this process is a multistep reaction, in which the insertion of CO2 seems to be the rate-determining step. Moreover, DFT studies show that the mechanism of the rearrangement between key intermediates, that is, the primary alkylzinc bicarbonate with a proximal position of hydrogen and the secondary alkylzinc bicarbonate with a distal position of hydrogen, most likely proceeds through internal rotation of the dinuclear bicarbonate. [ABSTRACT FROM AUTHOR]

The kinetic resolution of Z and E olefins by [2+2] cycloaddition with ketenes allows the isolation of pure E olefin, as well as the synthesis of pure cis-cyclobutanones, starting from Z/E mixtures. A computational rationale for this kinetic difference is reported. The obtained difference of energy of activation matches with the experimental results. [ABSTRACT FROM AUTHOR]

We have established that bipyridinium radicals can be reversibly π-dimerized under the combined effects of chemical (proton transfer) and electrochemical (electron transfer) stimuli. Our investigations also led to the discovery that a bis-pyridinyl appended calixarene intermediate is involved in a fully reversible redox-triggered σ-dimerization process. The structure of the most stable intramolecular σ-dimer was provided by computational chemistry and its complete conversion into a noncovalent π-dimer could be triggered chemically by addition of protons, leading to the formation of protonated cation radicals. Theoretical data collected with the N-methylated and N-protonated π-dimers also support the existence of multivariant orientations in π-bonded dimers of viologen cation-radicals. [ABSTRACT FROM AUTHOR]

α-Halogenoacetanilides (X=F, Cl, Br) were examined as H-bonding organocatalysts designed for the double activation of CO bonds through NH and CH donor groups. Depending on the halide substituents, the double H-bond involved a nonconventional CH⋅⋅⋅O interaction with either a HCX n ( n=1-2, X=Cl, Br) or a HCAr bond (X=F), as shown in the solid-state crystal structures and by molecular modeling. In addition, the catalytic properties of α-halogenoacetanilides were evaluated in the ring-opening polymerization of lactide, in the presence of a tertiary amine as cocatalyst. The α-dichloro- and α-dibromoacetanilides containing electron-deficient aromatic groups afforded the most attractive double H-bonding properties towards CO bonds, with a NH⋅⋅⋅O⋅⋅⋅HCX2 interaction. [ABSTRACT FROM AUTHOR]

The mechanism of the Pauson-Khand reaction has been studied by mass spectrometry and it has been found, through ion-molecule reaction with 13CO, that the carbon monoxide incorporated into the product cyclopentenone is one that has been retained within the complex. Theoretical and kinetic calculations support this finding, which provides a complementary explanation for the effect of Pauson-Khand promoters. [ABSTRACT FROM AUTHOR]