On the Cl···N halogen bond: a rotational study of CF3Cl···NH3

The rotational spectra of six isotopologues (CF(3)(35)Cl···(14)NH(3), CF(3)(37)Cl···(14)NH(3), CF(3)(35)Cl···(15)NH(3), CF(3)(37)Cl···(15)NH(3), CF(3)(35)Cl···(14)ND(3) and CF(3)(37)Cl···(14)ND(3)) of the CF(3)Cl···NH(3) adduct have been investigated and analyzed by pulsed jet Fourier transform microwave spectroscopy. Rotational, centrifugal distortion and quadrupole ((35)Cl, (37)Cl, (14)N) coupling constants have been precisely obtained. The two subunits of the complex are held together via a Cl···N halogen bond interaction. Information on the internal dynamics and on the dissociation energy of the complex is provided.     

Ultrasonic and ir investigations of N–H bond complexes

Complex formation of 1?:?1 mixtures of naphthols, viz. (α-naphthol and β-naphthol) with triethylamine in benzene have been studied at a frequency of 2?MHz in the concentration range of 0.010–0.090 and at varying temperatures of 30, 40 and 50°C. Using the measured ultrasonic velocity, the thermoacoustical parameters such as adiabatic compressibility, intermolecular free length, molar sound velocity, molar compressibility and acoustic impedance have been calculated. The ultrasonic velocity shows a maxima and adiabatic compressibility shows a corresponding minima as a function of concentration for these mixtures. These, in turn, are used to study the solute–solute interaction and the possibility of complex formation between unlike molecules of naphthols and triethylamine through intermolecular hydrogen bonding. The hydrogen bond is formed between hydrogen atom of naphthols and nitrogen atom of triethylamine molecule. The result obtained using infrared spectroscopy for both the systems also supports the existence of complex formation through intermolecular hydrogen bonding.     

Improved and expanded one-pot,two-component Boulton-Katritzky syntheses of N–N bond containing bicyclic heterocycles

Improved and expanded one-pot, two-component syntheses of bicyclic heterocycles containing a 3-N-acyl-3-amino-1,2-pyrazole motif from N′-hydroxy-carboxyamidines and acylbenzotriazoles have been developed. Importantly, this sequence obviates the need for hydrazine or N-aminating reagents to synthesize the key nitrogen–nitrogen (N–N) bond of these heterocycles, which is formed via Boulton-Katritzky rearrangement. A diverse array of pharmaceutically relevant N–N containing heterocycles has been prepared with this methodology using readily available reagents without the need for special equipment or conditions.     

Interaction of a C-F bond with the π-system of a C═C bond or "head on" with a proximate C-H bond

We describe the synthesis and preliminary study of two molecules, in which a fluorine atom is positioned proximately above the π-orbitals of a C═C bond or else wherein a C-F bond interacts in a "head on" fashion with a proximate C-H bond. The spectroscopic characteristics of these unusual interactions are documented, X-ray crystallographic analyses are reported, and theoretical calculations are employed to support the observed spectroscopy.     

Synthesis of benzoindoloquinolizines via a Cu(I)-mediated C–N bond formation

An effective synthesis of the multi ring-fused benzoindoloquinolizines has been accomplished by Cu(I)-mediated and MW-assisted C–N_amide bond formation of benzo[a]quinolizin-4-ones. The deamination of tetrahydro-2H-pyrido[2,1-a]isoquinolines was also studied and was found to give benzoquinolizines. The benzo[a]quinolizin-4-ones were prepared based on the annulations of C-1 substituted 3,4-dihydroisoquinolines and azlactones.     

Electrostatic,sequential bond energies and structures of Li+·(N2)n complexes: computational study

The MP2 and CCSD calculations of the geometries and binding energies of the Li⁺·(N₂)_n (n?=?1–4) complexes are obtained. The potential energy surface showed that these complexes exhibit one minimum state and one transition state. The mono- and di-ligated complexes exhibit linear configurations with a binding energy of 11.1 and 21.2 kcal mol^?1, respectively. Trigonal planar and tetrahedral configurations are obtained for tri- and tetra-ligated complexes, respectively. The computed sequential bond dissociation energies (BDEs) of Li⁺·(N₂)_n (n?=?1–4) complexes are also calculated in which the mono-ligated complex has the largest BDE value. The obtained trend is mainly dependent on the variation in the ion-quadrupole interaction of these ion complexes. These calculations predict that these complexes are of purely electrostatic nature.

     

Rotational spectra and properties of complexes B···ICF3 (B = Kr or CO) and a comparison of the efficacy of ICl and ICF3 as iodine donors in halogen bond formation

The ground-state rotational spectra of two weakly bound complexes B···ICF(3) (B = Kr or CO) formed by trifluoroiodomethane have been observed in pulsed jets by using two types of Fourier-transform microwave spectroscopy (chirped-pulse and Fabry-Perot cavity). Both complexes exhibit symmetric-top type spectra, thus indicating that the Kr atom in Kr···ICF(3) and both the C and O atoms in OC···ICF(3) lie along the C(3) axis of ICF(3). The rotational constant B(0), the centrifugal distortion constants D(J) and D(JK), and the iodine nuclear quadrupole coupling constant χ(aa)(I) were determined for each of the isotopologues (84)Kr···ICF(3), (86)Kr···ICF(3), (16)O(12)C···ICF(3), (16)O(13)C···ICF(3), and (18)O(12)C···ICF(3). Interpretation of the spectroscopic constants reveals that the carbon atom of CO is adjacent to I and participates in the weak bond in OC···ICF(3). Simple models based on unperturbed component geometries lead to the distances r(Kr···I) = 3.830(1) ? and r(C···I) = 3.428(1) ? in Kr···ICF(3) and OC···ICF(3), respectively, and to the quadratic force constants for stretching of the weak bond k(σ) = 2.80 N m(-1) and 3.96 N m(-1), respectively. The distances r(Z···I) (Z is the acceptor atom in B), the k(σ) values, and the angular geometries of the pair of complexes B···ICF(3) and B···ICl for a given B are compared when B = Kr, CO, H(2)O, H(2)S, or NH(3). The comparison reveals that the iodine bond in B···ICF(3) is systematically longer and weaker than that of B···ICl, while the angular geometry of the B···I moiety is isomorphic in B···ICF(3) and B···ICl for a given B. It is concluded that -CF(3) is less effective than -Cl as an electron-withdrawing group when attached to an I atom and that the angular geometries of the B···ICF(3) can be predicted by means of a simple rule that holds for many hydrogen- and halogen-bonded complexes.     

N[bond]C(alpha) bond dissociation energies and kinetics in amide and peptide radicals. Is the dissociation a non-ergodic process?

Dissociations of aminoketyl radicals and cation radicals derived from beta-alanine N-methylamide, N-acetyl-1,2-diaminoethane, N(alpha)-acetyl lysine amide, and N(alpha)-glycyl glycine amide are investigated by combined density functional theory and M?ller-Plesset perturbational calculations with the goal of elucidating the mechanism of electron capture dissociation (ECD) of larger peptide and protein ions. The activation energies for dissociations of N[bond]C bonds in aminoketyl radicals decrease in the series N[bond]CH(3) > N-CH(2)CH(2)NH(2) > N[bond]CH(2)CONH(2) approximately N[bond]CH(CONH(2))(CH(2))(4)NH(2). Transition state theory rate constants for dissociations of N[bond]C(alpha) bonds in aminoketyl radicals and cation-radicals indicate an extremely facile reaction that occurs with unimolecular rate constants >10(5) s(-1) in species thermalized at 298 K in the gas phase. In neutral aminoketyl radicals the N[bond]C(alpha) bond cleavage results in fast dissociation. In contrast, N[bond]C(alpha) bond cleavage in aminoketyl cation-radicals results in isomerization to ion-molecule complexes that are held together by strong hydrogen bonds. The facile N[bond]C(alpha) bond dissociation in thermalized ions indicates that it is unnecessary to invoke the hypothesis of non-ergodic behavior for ECD intermediates.     

Nickel-catalyzed cooperative B-H bond activation for hydroboration of N‑heteroarenes,ketones and imines

We report two air-stable nickel(II) half-sandwich complexes, Cp*Ni(1,2-Cy₂PC₆H₄O) (1) and Cp*Ni(1,2-Ph₂PC₆H₄NH) (2), for cooperative B-H bond activation and their applications in catalytic hydroboration of unsaturated organic compounds. Both 1 and 2 react with HBpin by adding the B-H bond across the Ni−X bond (X = O or N), giving rise to the 18-electron Ni(II)−H active species, [H1(Bpin)] and [H2(Bpin)]. Subtle tuning of the Ni−X pair and the supporting ancillary phosphine have a significant effect on the reactivity and catalytic performance of Cp*Ni(1,2-R₂PC₆H₄X). Unlike [H2(Bpin)], the activation of HBpin in [H1(Bpin)] is reversible, which enables the Ni−O complex to be an effective cooperative catalyst in the hydroboration of N-heteroarenes, and as well as ketones and imines.     

The role of triplet repulsion in alkyl radical addition to a 7π-C-O bond and alkoxy radical addition to a π-C-C bond

The experimental activation energies of the R^• + O = CR¹R² and RO^• + CH₂ = CHR¹ addition reactions are analyzed within the framework of the parabolic model of the bimolecular addition reaction. The activation energy also depends on the dissociation energy of the forming C-O bond and on the reaction enthalpy: the higher the dissociation energy, the higher the activation energy. The empirical relationshipr _e J..D _e = 0.97 x 10-¹³ m kJ.-¹ mol is found for H^•, Cl^•, Br^{• •} and RO^• radical addition to multiple C=C and C=O bonds (r_e is the distance between the peaks of the intersecting parabolic curves). This is due to the effect of the triplet repulsion on radical addition. The interaction of polar groups and the steric effect also influence the activation energy.     

Static and dynamic descriptions of bond breaking/formation: a complementary view?

Ab initio molecular-dynamic simulations using density-functional theory and the recent atom-centered density-matrix propagation (ADMP) method were used to study the bond breaking and formation for a case-study substitution nucleophilic bimolecular reaction, namely, the Walden inversion. Using the atoms-in-molecule approach, we have performed a detailed analysis to investigate intra- and intermolecular charge transfer along the ADMP trajectory. These results were compared to those obtained considering a static approach, such as the intrinsic reaction path. In particular, the topological properties computed along the dynamic trajectory well evidence a stronger electron exchange tending to spontaneously maximize the rising covalent interaction. Furthermore, their analysis suggests that the bond formation mechanism involves a reactive intermediate with a bonding interaction stronger than in the final product.     

Possible intramolecular rearrangements of O-vinyloximes initiated by N—O bond dissociation: a quantum-chemical analysis

The potential surface of conformational transitions of O-vinylacetoxime was studied and the regions of starting states for possible isomeric transformations with the N—O bond dissociation as the limiting stage were recognized. The activation parameters and heat effects of intramolecular rearrangement O-vinylacetoxime iminoacetaldehyde were evaluated. Transition-state structure of the rearrangement was identified.     

Ring opening of heterocycles containing a C–N double bond: a simple synthesis of imides promoted by acyl palladium species

A detailed study on the reactivity of various heterocycles, containing a C–N double bond, with acyl palladium species, generated in situ from allyl or benzyl halides and CO, has been performed. While the cyclic imine 2-methyl-1-pyrroline reacted with acyl-palladium intermediates to give a bicyclic β-lactam, other heterocycles containing a C–N double bond conjugated with a heteroatom (O or N), showed a ring-opening reaction leading to functionalized imides with high structural diversity. Such methodology represents a simple and direct way to prepare structurally complex imides. Moreover, a reaction mechanism, involving cationic intermediates, was also proposed.     

Synthesis,structure and reactivity of complexes containing a transition metal–bismuth bond

The transition metal chemistry of bismuth has attracted significant interest since the 1970s. The low cost and high abundance of bismuth(III) reagents, such as the trihalides, makes them ideal starting materials and the size of the bismuth centre allows three- and higher-coordinate complexes to be synthesised, in which the bismuth atom is linked to one or more transition metal fragments. The ability to vary these metal fragments gives access to a plethora of available structures, with cyclopentadienylcarbonyl, metal carbonyl and sandwich compounds of bismuth in existence. Significant recent study has focused on applications in catalysis, where bismuth species can act as cross-coupling agents in carbon–carbon, carbon–nitrogen and carbon–oxygen bond forming reactions. Another striking feature is the variation in bonding situations that can be observed when studying the organometallic chemistry of bismuth. For example, dative and covalent interactions have been reported, in addition to cases of dibismuth acting as a two-, four- or six-electron donating ligand. This review aims to demonstrate the multi-faceted nature of the transition metal chemistry of bismuth and provide a detailed coverage of this topic.     

Porpholactams and chlorolactams: replacement of a β,β'-double bond in meso-tetraphenyl-porphyrin and -chlorin by a lactam moiety

Reaction of meso-tetraphenylporpholactone with hydrazine converts the lactone moiety to an N-aminolactam. It also reduces the opposite pyrrolic moiety of both the starting material and the N-aminolactam, generating chlorin-like chlorolactone and N-aminochlorolactam, respectively. Reductive N-N cleavage of the N-aminoporpholactam generates the parent porpholactam.     

Experimental and theoretical study of the dissociation enthalpy of the N–O bond on 2-hydroxypyridine N-oxide: theoretical analysis of the energetics of the N–O bond for hydroxypyrydine N-oxide isomers

The standard (p^∘=0.1 MPa) molar enthalpy of formation of crystalline 2-hydroxypyridine N-oxide was measured, at T=298.15 K, by static bomb calorimetry and the standard molar enthalpy of sublimation, at T=298.15 K, was obtained using Calvet microcalorimetry. These values were used to derive the standard molar enthalpy of formation of 2-hydroxypyridine N-oxide in gaseous phase, and to evaluate the dissociation enthalpy of the N–O bond. Additionally, high-level density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional have been performed for the three isomers of hydroxypyridine N-oxide in order to confirm the experimental trend for the dissociation enthalpy of the (N–O) bond.     

Location of protons in N-H···N hydrogen-bonded systems: a theoretical study on intramolecular pyridine-dihydropyridine and pyridine-pyridinium pairs

Two-dimensional potential energy surfaces (PESs) were calculated for the degenerate intramolecular proton transfer (PT) in two N-H···N hydrogen-bonded systems, (Z)-2-(2-pyridylmethylidene)-1,2-dihydropyridine (1) and monoprotonated di(2-pyridyl) ether (2), at the MP2/cc-pVDZ level of theory. The calculated PES had two minima in both cases. The energy barrier in 1 was higher than the zero-point energy (ZPE) level, while that in 2 was close to the ZPE. Vibrational wavefunctions were obtained by solving time-independent Schr?dinger equations with the calculated PESs. The maximum points of the probability density were shifted from the energy minima towards the region where the covalent N-H bond was elongated and the N···N distance shortened. The effects of a polar solvent on the PES were investigated with the continuum or cluster models in such a way that the solute-solvent electrostatic interactions could be taken into account under non-equilibrated conditions. A solvated contact ion-pair was modelled by a cluster consisting of one cation 2, one chloride ion and 26 molecules of acetonitrile. The calculation with this model suggested that the bridging proton is localised in the deeper well due to the significant asymmetry of the PES and the high potential barrier.