Characterization of the N?H···ON and N?H···NO H‐bonds in nitrosamine dimers

Ab initio molecular orbital and DFT calculations have been carried out for three most stable dimers of parent nitrosamine (NA) in order to elucidate the structures and energetics of the dimers. The structures were optimized using HF, B3LYP, and MP2 methods with 6‐311+G(d,p) and 6‐311++G(2d,2p) basis sets. At the optimized geometries obtained at MP2/6‐311++G(2d,2p) level of theory, the energies were evaluated at QCISD/aug‐cc‐pVDZ and CCSD/aug‐cc‐pVDZ levels. The most stable dimer has two N? H···O?N hydrogen bonds and the least stable dimer has two N? H···N?O hydrogen bonds. The natural bond orbital analysis showed that the lpO(N) → BD*(N? N) and lpO(N) → BD*(N? H_b) interactions play a decisive role in the stabilization of the NH···O(N) hydrogen bonds in dimers. The atoms in molecules results reveal that the intermolecular N? H···O(N) H‐bonds in dimers have electrostatic character. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Intermolecular interactions in group 14 hydrides: Beyond C?H···H?C contacts

In line with previous work in which we established the factors that enhance attractive C? H···H? C dihydrogen interactions in alkanes, an extended theoretical analysis of noncovalent intermolecular interactions in group 14 hydrides is presented here. Remarkably, these weak interactions may play a major role in determining the crystal structures adopted by several families of molecules. A combined structural and computational analysis at the MP2 level allowed us to identify and characterize different interactions of the type E? H···H? E and E···H? E (E = Si, Ge, Sn, and Pb), and to find also the most suitable scenario for the establishment of each particular type. The nature of the interactions has been analyzed in terms of natural charges of the atoms involved and a topological analysis of the electron density of several dimers confirms the existence of H···H and H···E attractive contacts. We have observed that the interaction strength increases when descending down the periodic group and that silicon has a marked tendency to establish Si···H? Si interactions. A size‐dependent backbone effect that reinforces H···H dihydrogen interactions in polyhedral systems has also been found.     

N?H···S and S?H···N intramolecular hydrogen bond in β‐thioaminoacrolein: A quantum chemical study

The conformational study of β‐thioaminoacrolein was performed at various theoretical levels, HF, B3LYP, and MP2 with 6‐311++G(d,p) basis set, and the equilibrium conformations were determined. To have more reliable energies, the total energies of all conformers were recomputed at high‐level ab initio methods, G2MP2, G3, and CBS‐QB3. According to these calculations, the intramolecular hydrogen bond is accepted as the origin of conformational preference in thialamine (TAA) and thiolimine groups. The hydrogen bond strength in various resonance‐assisted hydrogen bond systems was evaluated by HB energy, geometrical parameters, topological parameters, and charge transfers corresponding to orbital interactions. Furthermore, our results reveal that the TAA tautomer has extra stability with respect to the other tautomers. The population analyses of the possible conformations by NBO predict that the origin of this preference is mainly due to the π‐electron delocalization in framework of TAA forms, especially usual π_C?C → π*_C?S and Lp (N) → π*_C?C charge transfers. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Cooperative influence of water binding to peptides by N?H···OH2 and CO···HOH hydrogen bonds: Study by Ab Initio calculations

In this article, the geometry structures of hydrogen bond chains of formamide and N‐methylacetamide and their hydrogen‐bonded complexes with water were optimized at the MP2/6‐31G* level. Then, we performed Møller–Plesset perturbation method with 6‐311++g**, aug‐cc‐pvtz basis sets to study the cooperative influence to the total hydrogen bond energy by the N? H ··· OH₂ and C?O ··· HOH hydrogen bonds. On the basis of our results, we found that the cooperativity of the hydrogen‐bonded complexes become weaker as N? H ··· OH₂ and C?O ··· HOH hydrogen bonds replacing N? H ··· O?C hydrogen bonds in protein and peptide. It means that the N? H and C?O bonds in peptide prefer to form N? H ··· O?C hydrogen bond rather than to form C?O ··· HOH and N? H ··· OH₂. It is significant for understanding the structures and properties of the helical or sheet structures of protein and peptide in biological systems. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Theoretical study of the S?H···O blue‐shifted hydrogen bond

Theoretical calculations were performed to study the nature of the hydrogen bonds in the complexes HCHO···HSO, HCOOH···HSO, HCHO···HOO, and HCOOH···HOO. The geometric structures and vibrational frequencies of these four complexes at the MP2/6‐31G(d,p) and MP2/6‐311+G(d,p) levels are calculated by standard and counterpoise‐corrected methods, respectively. The results indicate that in the complexes HCHO···HSO and HCOOH···HSO the S? H bond is strongly contracted. In the S? H···O hydrogen bonds, the calculated blue shifts for the S? H stretching frequencies are in the vicinity of 50 cm^?1. While in the complexes HCHO···HOO and HCOOH···HOO, the O? H bond is elongated and O? H···O red‐shifted hydrogen bonds are found. From the natural bond orbital analysis it can be seen that the X? H bond length in the X? H···Y hydrogen bond is controlled by a balance of four main factors in the opposite directions: hyperconjugation, electron density redistribution, rehybridization, and structural reorganization. Among them hyperconjugation has the effect of elongating the X? H bond. Electron density redistribution and rehybridization belong to the bond shortening effects, while structural reorganization has an uncertain influence on the X? H bond length. In the complexes HCHO···HSO and HCOOH···HSO, the shortening effects dominate which lead to the blue shift of the S? H stretching frequencies. In the complexes HCHO···HOO and HCOOH···HOO where elongating effects are dominant, the O? H···O hydrogen bonds are red‐shifted. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

N-alkyl-C-polyfluoroalkyl-C-chlorosulfinimides RFC(Cl)SN?R

The N-alkyl-C-polyfluoroalkyl-C-chlorosulfinimides R_FC(Cl)SN R have been investigated. Some aspects of their thermal stability and their [3 + 2] and [3 + 1] cycloaddition reactions have been examined.     

An efficient synthesis of phosphenimidous esters,RO?PN?Ar

Trimethylsilyltrifluoromethane sulfonate is shown to be an efficient catalyst for the elimination of Me₃SiCl from N-trimethylsilyl-N-(2,4,6-tri-tert-butylphenyl)amidochlorophosphites la-f , leading to the phosphenimidous esters 3a–f. The crystal structures of phosphites 1a and 1d provide a stereochemical explanation for the better thermal stability of 1d On the basis of these observations a convenient and general synthesis of phosphenimidous esters 3a–f is presented.     

Attempted 1,3-trimethylsilyl migration in Me3Si?PSN?R system

A dimer of thioxo-N-t-butylimino(trimethylsiloxy)-phosphorane 5 has been prepared by reaction of tris(trimethylsilyl) phosphine with N-sulfinyl-N-tert-butylamine. The structure of 5 has been confimed by X-ray analysis data. 1-Aza-2-thia-3-phosphaallene 1 , thiaphosphaziridine 3 , iminophosphine P-sulfide 4 are postulated as intermediates of the reaction studied.     

An insight into C?H···N hydrogen bond and stability of the complexes formed by trihalomethanes with ammonia and its monohalogenated derivatives

A theoretical study of the C? H···N hydrogen bond in the interactions of trihalomethanes CHX₃ (X = F, Cl, Br) with ammonia and its halogen derivatives NH₂Y (Y = F, Cl, Br) has been carried out thoroughly. The complexes are quite stable, and their stability increases in going from CHF₃ to CHCl₃ then to CHBr₃ when Y keeps unchanged. With the same CHX₃ proton donor, enhancement of the gas phase basicity of NH₂Y strengthens stability of the CHX₃···NH₂Y complex. The C? H···N hydrogen bond strength is directly proportional to the increase of proton affinity (PA) at N site of NH₂Y and the decrease of deprotonation enthalpy (DPE) of C? H bond in CHX₃. The CHF₃ primarily appears to favor blue shift while the red‐shift is referred to the CHBr₃. The blue‐ or red‐shift of CHCl₃ strongly depends on PA at N site of NH₂Y. We suggest the ratio of DPE/PA as a factor to predict which type of hydrogen bond is observed upon complexation. The SAPT2+ results show that all C? H···N interactions in the complexes are electrostatically driven regardless of the type of hydrogen bond, between 48% and 61% of the total attractive energy, and partly contributed by both induction and dispersion energies.     

Metal‐Catalyzed α‐Arylation of Carbonyl and Related Molecules: Novel Trends in C?C Bond Formation by C?H Bond Functionalization

α‐Arylated carbonyl compounds are commonly occurring motifs in biologically interesting molecules and are therefore of high interest to the pharmaceutical industry. Conventional procedures for their synthesis often result in complications in scale‐up, such as the use of stoichiometric amounts of toxic reagents and harsh reaction conditions. Over the last decade, significant efforts have been directed towards the development of metal‐catalyzed α‐arylations of carbonyl compounds as an alternative synthetic approach that operates under milder conditions. This Review summarizes the developments in this area to date, with a focus on how the substrate scope has been expanded through selection of the most appropriate synthetic method, such as the careful choice of ligands, precatalysts, bases, and reaction conditions.     

Transition‐metal‐catalyzed aminations and aziridinations of C?H and CC bonds with iminoiodinanes

Catalytic insertion or addition of a metal‐imido/nitrene species, generated from reaction of a transition‐metal catalyst with iminoiodanes, to C? H and C?C bonds offers a convenient and atom economical method for the synthesis of nitrogen‐containing compounds. Following this groundbreaking discovery during the second half of the last century, the field has received an immense amount of attention with a myriad of impressive metal‐mediated methods for the synthesis of amines and aziridines having been developed. This review will cover the significant progress made in improving the efficiency, versatility and stereocontrol of this important reaction. This will include the various iminoiodanes, their in situ formation, and metal catalysts that could be employed and new ligands, both chiral and non‐chiral, which have been designed, as well as the application of this functional group transformation to natural product synthesis and the preparation of bioactive compounds of current therapeutic interest. DOI 10.1002/tcr.201100018     

Rhodium(III)‐Catalyzed C?C and C?O Coupling of Quinoline N‐Oxides with Alkynes: Combination of C?H Activation with O‐Atom Transfer

[Cp*Rh^III]‐catalyzed C H activation of arenes assisted by an oxidizing N O or N N directing group has allowed the construction of a number of hetercycles. In contrast, a polar N O bond is well‐known to undergo O‐atom transfer (OAT) to alkynes. Despite the liability of N O bonds in both C H activation and OAT, these two important areas evolved separately. In this report, [Cp*Rh^III] catalysts integrate both areas in an efficient redox‐neutral coupling of quinoline N‐oxides with alkynes to afford α‐(8‐quinolyl)acetophenones. In this process the N O bond acts as both a directing group for C H activation and as an O‐atom donor.     

Application of a C?C Bond‐Forming Conjugate Addition Reaction in Asymmetric Dearomatization of β‐Naphthols

A C C bond‐forming conjugate reaction was successfully applied to the enantioselective dearomatization of β‐naphthols. A C(sp2) C(sp3) bond is formed by using propargylic ketones as reactive partners. Good to excellent Z/E ratios and ee values were obtained by employing an in situ generated magnesium catalyst. Further transformations of the Z‐configured C C double bond in the products were achieved under mild reaction conditions. Moreover, the stereocontrolling element of this magnesium‐catalyzed dearomatization reaction was explored by computational chemistry.     

Does a Stabilising Interaction Favouring the Z,Z Configuration of ?S‐NSN‐S? Systems Exist?

The existence of the orbital interaction presented in the literature as being the cause for the stabilisation of the Z,Z configuration of Ph-S-N=S=N-S-Ph (1) and its derivatives in the crystal phase, has been investigated. The results of theoretical calculations at the DFT/B3LYP/6-311+G* level of theory suggest that such a stabilising interaction might not exist or be extremely weak and that packing forces must be the main cause of the observed Z,Z configuration in the solid. To reach this conclusion structural and energetic parameters were combined to study the bonding in these -S-N=S=N-S- systems. For the analogous Ph-Se-N=S=N-Se-Ph (2) in particular the isomeric equilibrium in solution found in the variable-temperature 77Se NMR spectrum indicates that, in the gas phase or in solution, the observed Z,Z configuration is not stabilised to a greater extent than the Z,E configuration.     

Direct α‐Arylation of Ethers through the Combination of Photoredox‐Mediated C?H Functionalization and the Minisci Reaction

The direct α‐arylation of cyclic and acyclic ethers with heteroarenes has been accomplished through the design of a photoredox‐mediated C H functionalization pathway. Transiently generated α‐oxyalkyl radicals, produced from a variety of widely available ethers through hydrogen atom transfer (HAT), were coupled with a range of electron‐deficient heteroarenes in a Minisci‐type mechanism. This mild, visible‐light‐driven protocol allows direct access to medicinal pharmacophores of broad utility using feedstock substrates and a commercial photocatalyst.