Halogen bonding between substituted chlorobenzene and trimethylamine: Decisive role of σ–hole and C?Cl bond breaking energy

Theoretical studies have been carried out on the halogen bonding interaction between para substituted chlorobenzene (Y C₆H₄Cl, Y = H, NH₂, CH₃, F, CN, NO₂) and N(CH₃)₃ using ab initio MP2/aug‐cc‐pVDZ and DFT based wB97XD/6‐311++G(d,p) methods. The positive electrostatic potential (V_S,max) on the Cl atom and the heterolytic bond breaking enthalpy of the C Cl bond have been calculated and their role on halogen bonding is discussed. The heterolytic bond breaking enthalpy of the C Cl bond is proposed as a measure of the strength of the σ‐hole on Cl atom. The binding strength of the complexes ranging between −6.13 kJ mol⁻¹ and −9.29 kJ mol⁻¹ are linearly related to the V_S,max of the Cl atom and the bond breaking enthalpy of the C Cl bond. In addition, energy decomposition analysis was performed on the halogen bonded complexes via symmetry adapted perturbation theory (SAPT) to predict the dominant energy component and the nature of the N···Cl interaction.     

Nature of MoH···I bonds in Cp2Mo(L)H···I‐C≡C‐R Complexes (L=H,CN, PPh2, C(CH3)3; R=NO2, Cl,Br, H,OH, CH3, NH2)

The nature of the MoH···I bond in Cp₂Mo(L)H···I‐C≡C‐R (L= H, CN, PPh₂, C(CH₃)₃; R=NO₂, Cl, Br, H, OH, CH₃, NH₂) was investigated using electrostatic potential analysis, topological analysis of the electron density, energy decomposition analysis and natural bond orbital analysis. The calculated results show that MoH···I interactions in the title complexes belong to halogen‐hydride bond, which is similar to halogen bonds, not hydrogen bonds. Different to the classical halogen bonds, the directionality of MoH···I bond is low; Although electrostatic interaction is dorminant, the orbital interactions also play important roles in this kind of halogen bond, and steric interactions are weak; the strength of H···I bond can tuned by the most positive electrostatic potential of the I atom. As the electron‐withdrawing ability of the R substituent in the alkyne increases, the electrostatic potential maximum of the I atom increases, which enhances the strength of the H···I halogen bond, as well as the electron transfer.     

Mass spectra of monosubstituted trans-stilbenes

The mass spectra of twenty-eight monosubstituted trans-stilbenes in ortho, meta, para and alpha positions with ? N(CH₃)₂, ? NH₂, ? OCH₃, ? OH, ? Br, ? Cl, ? F, ? CH₃, ? COOH, ? CN and ? NO₂ groups as substituents have been studied. A detailed fragmentation pathway is given for stilbene. This fragmentation, characteristic for most of the substituted stilbenes, takes place either from the molecular or from the [M - Substituent] ion. In o-nitro-, o-methoxy-,α-carboxyl- and α-methylstilbene, however, rearrangement reactions prior to fragmentation influence the fragmentation pattern.     

A computational study on the ring stretching modes of halogen‐substituted pyridine involved in H‐bonding

Density functional method B3LYP plus the AUG‐cc‐pVDZ and AUG‐cc‐pVTZ basis sets is used to investigate ring normal modes of halogen‐substituted pyridines involved in the N ··· H? X H‐bonds with HX (X = F, Cl). The results demonstrated that the formation of hydrogen bond leads to an increase in the frequencies of the ring breathing mode v₁, the N‐para‐C stretching mode v_6a and the meta‐CC stretching mode v_8a, whereas there is no change in the triangle mode v₁₂ for free pyridine and a smaller blue shift for substituted pyridines. There is a strong coupling between the C? Y stretching vibration and the triangle mode (ortho‐ and para‐substituted) or the breathing mode (meta‐substituted) in substituted pyridines, which leads to the frequency decrease in the triangle or breathing modes. The natural bond orbital analysis suggests that electrostatic interaction and charge transfer caused by the intermolecular and intramolecular hyperconjugations are the origin of the frequency blue shift in the ring stretching modes. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Weak hydrogen and halogen bonding in 4‐[(2,2‐difluoroethoxy)methyl]pyridinium iodide and 4‐[(3‐chloro‐2,2,3,3‐tetrafluoropropoxy)methyl]pyridinium iodide

To enable a comparison between a C—H…X hydrogen bond and a halogen bond, the structures of two fluorous‐substituted pyridinium iodide salts have been determined. 4‐[(2,2‐Difluoroethoxy)methyl]pyridinium iodide, C₈H₁₀F₂NO⁺·I⁻, (1), has a –CH₂OCH₂CF₂H substituent at the para position of the pyridinium ring and 4‐[(3‐chloro‐2,2,3,3‐tetrafluoropropoxy)methyl]pyridinium iodide, C₉H₉ClF₄NO⁺·I⁻, (2), has a –CH₂OCH₂CF₂CF₂Cl substituent at the para position of the pyridinium ring. In salt (1), the iodide anion is involved in one N—H…I and three C—H…I hydrogen bonds, which, together with C—H…F hydrogen bonds, link the cations and anions into a three‐dimensional network. For salt (2), the iodide anion is involved in one N—H…I hydrogen bond, two C—H…I hydrogen bonds and one C—Cl…I halogen bond; additional C—H…F and C—F…F interactions link the cations and anions into a three‐dimensional arrangement.     

The intermolecular interaction in the charge-transfer complexes between amines and halogens: A theoretical characterization of the trends in halogen bonding

The trends in the properties of prereactive or charge-transfer complexes formed between the simple amines NH₃, CH₃NH₂, (CH₃)₂NH, and (CH₃)₃N and the halogens F₂, ClF, Cl₂, BrF, BrCl, and Br₂ were investigated by the ab initio restricted Hartree–Fock approach, the Møller–Plesset second-order method, and with several density functional theory variants using extended polarized basis sets. The most important structural parameters, the stabilization energies, the dipole moments, and other quantities characterizing the intermolecular halogen bond in these complexes are monitored, discussed, and compared. A wide range of interaction strengths is spanned in these series. Successive methyl substitution of the amine as well as increasing polarities and polarizabilities of the halogen molecules both systematically enhance the signature of charge-transfer interaction. These trends in halogen bonds of varying strength, in many aspects, parallel the features of hydrogen bonding.     

Computational study of topological effects on intramolecular electron transfer in mixed-valence compounds

The constrained density functional theory (CDFT) was used to investigate the topological effects on intramolecular electron transfer processes that have been reported in previous experimental work [Inorg. Chem., 1997, 36 (22), pp 5037–5049]. The computation mainly focused on three isomers of diferrocenylbenzenes (ortho, para, and meta) and 5-substituted derivatives of m-diferrocencylbenzenes with R = NH₂, Cl, CH₃, CN, NO₂, NeCH₃)₃³⁺, and N₂⁺. The influence of a third group R′ (R′ = NH₂ and N₂⁺) was introduced to the ortho and para isomers. The calculations were compared with the experimental results. The relation between the substituted functional groups and the effectiveness of intramolecular electron transfer was discussed on the basis of CDFT computational results.     

A theoretical analysis of substituted aromatic compounds

The substituents ? CH₃, ? F, ? NO₂, ? OCH₃, and ? CH₂?CH₂ were placed at the ortho, meta, and para positions on the aromatic molecules aniline, benzaldehdye, nitrobenzene, and phenol. MMFF94, AM1, B3LYP, M06, M06‐2X, ωB97X, ωB97X‐d, and RI‐MP2 using cc‐pVDZ and cc‐pVTZ and CCSD(T) with cc‐pVDZ basis sets were used to calculate the geometries and energies of all regiomers of the molecules. Relative energies of the ortho and meta regiomers relative to the para regiomers were calculated and compared to the CCSD(T) values. A good basis set correlation between cc‐pVDZ and cc‐pVTZ was observed in RI‐MP2. Overall, RI‐MP2 gave the best correlation with the CCSD(T) results. All of the hybrid functionals showed similar accuracy and could effectively describe the intramolecular hydrogen‐bonding interactions of these compounds. The methoxy group at the para position in methoxyaniline, methoxyphenol, methoxynitrobenzene, and methoxybenzaldehyde was rotated around the phenyl‐O bond. HF, along with the cc‐pVDZ basis with the other methods, generated inaccurate energy profiles for p‐methoxyphenol. For the density functional theory methods, it was necessary to use improved grids to get smooth curves. © 2013 Wiley Periodicals, Inc.     

Effect of the Electronic Structure of Substituents at the Silicon Atom on the Structure and Bond Energies of Methylhydrosilanes and Silenes

Ab initiocalculations with full geometry optimization were performed for methylhydrosilanes R₂HSiCH₃, dimethylsilanes C₂Si(CH₃)₂, and silenes R₂Si = CH₂ (R = H, CH₃, SiH₃, CH₃O, NH₂, Cl, F). The enthalpies of dehydrogenation methylhydrosilanes into silenes and of dehydrocondesation of methylhydrosilanes into dimethylsilanes were calculated. The enthalpies of dehydrogenation and dehydrocondensation increase with the electronegativity of substituent R. The Si-C and Si = C bond energies were calculated. As the electronegativity of the substituent increases, the Si-C bond shortens and strengthens, while the Si = C bond shortens and weakens.     

氰化物与吡咯复合物氢键强度的理论研究

The R-C≡N…pyrrole (R=H, CH3, CH2F, CHF2, CF3, NH2, BH2, OH, F, CH2Cl, CHCl2, CCl3, Li, Na) complexes were considered as the simple sample for measure of hydrogen bonding strength. Density functional theory B3LYP/6-311 G^** level was applied to the optimization of geometries of complexes and monomers. Measure of hydrogen bonding strength based on geometrical and topological parameters, which were derived from the AIM theory, was analyzed. Additionally, natural bond orbital (NBO) analysis and frequency calculations were performed.From the computation results it was found that the electronic density at N-H bond critical points was also strictly correlated with the hydrogen bonding strength.     

Simultaneous Chain‐Growth and Step‐Growth Polymerization of Methoxystyrenes by Rare‐Earth Catalysts

The simultaneous chain‐growth and step‐growth polymerization of a monomer is of great interest and importance because it can produce unique macromolecules which are difficult to prepare by other means. However, such a transformation is usually difficult to achieve in one polymerization system because chain‐growth polymerization and step‐growth polymerization proceed by different reaction mechanisms. Reported here is the simultaneous chain‐growth and step‐growth polymerization of para‐ and meta‐methoxystyrenes catalyzed by half‐sandwich rare‐earth alkyl complexes, and the step‐growth polymerization proceeds by the C?H polyaddition of anisyl units to vinyl groups. This unprecedented transformation affords a new family of macromolecules containing unique alternating anisole‐ethylene sequences. In contrast to para‐ and meta‐methoxystyrenes, ortho‐methoxystyrene exclusively undergo syndiospecific, living chain‐growth polymerization by continuous C=C bond insertion to give perfect syndiotactic poly(ortho‐methoxystyrene) with high molecular weight and narrow polydispersity (rrrr >99 %, M_n up to 280 kg mol^?1, M_w/M_n <1.10).     

Bond dissociations in hypervalent ammonium radicals prepared by collisional neutralization of protonated six-membered nitrogen heterocycles

Hypervalent organic ammonium radicals were generated by collisional neutralization with dimethyl disulfide of protonated 1,4-diazabicyclo[2.2.2]octane (1H⁺), N,N′-dimethylpiperazine (2H⁺) and N-methylpiperazine (3H⁺). The radicals dissociated completely on the 5.1 μs time-scale. Radical 1H^• underwent competitive N−H and N−C bond dissociations producing 1,4-diazabicyclo[2.2.2]octane and small ring fragments. Dissociations of radical 2H^• proceeded by N−H bond dissociation and ring cleavage, whereas N−CH₃ bond cleavage was less frequent. Radical 3H^• underwent N−H, N−CH₃ and N−C_ring bond cleavages followed by post-reionization dissociations of the formed cations. The pattern of bond dissociations in the hypervalent ammonium radicals derived from six-membered nitrogen heterocycles is similar to those of aliphatic ammonium radicals. © 1997 John Wiley & Sons, Ltd.     

Unconventional H‐bonds: SH···N interaction

Quantum calculations at the MP2/aug‐cc‐pVDZ level are used to analyze the SH···N H‐bond in complexes pairing H₂S and SH radical with NH₃, N(CH₃)₃, NH₂NH₂, and NH₂N(CH₃)₂. Complexes form nearly linear H‐bonds in which the S? H covalent bond elongates and shifts its stretching frequency to the red. Binding energies vary from 14 kJ/mol for acceptor NH₃ to a maximum of 22 kJ/mol for N(CH₃)₃ and N(CH₃)₂NH₂. Analysis of geometric, vibrational, and electronic data indicate that the SH···N interaction involving SH is slightly stronger than that in which the closed‐shell H₂S serves as donor. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Cover Feature: An Exploration of the Hydrogen Bond Donor Ability of Ammonia (ChemPhysChem 20/2023)

Ammonia is an important molecule due to its wide use in the fertiliser industry. It is also used in aminolysis reactions. Theoretical studies of the reaction mechanism predict that in reactive complexes and transition states, ammonia acts as a hydrogen bond donor forming N−H⋅⋅⋅O hydrogen bond. Experimental reports of N−H⋅⋅⋅O hydrogen bond, where ammonia acts as a hydrogen bond donor are scarce. Herein, the hydrogen bond donor ability of ammonia is investigated with three chalcogen atoms i. e. O, S, and Se using matrix isolation infrared spectroscopy and electronic structure calculations. In addition, the chalcogen bond acceptor ability of ammonia has also been investigated. The hydrogen bond acceptor molecules used here are O(CH₃)₂, S(CH₃)₂, and Se(CH₃)₂. The formation of the 1 : 1 complex has been monitored in the N−H symmetric and anti-symmetric stretching modes of ammonia. The nature of the complex has been delineated using Atoms in Molecules analysis, Natural Bond Orbital analysis, and Energy Decomposition Analysis. This work presents the first comparison of the hydrogen bond donor ability of ammonia with O, S, and Se.     

Synthesis and Complexation Study of New Aminoalkynyl−amidinate Ligands

The current library of amidinate ligands has been extended by the synthesis of two novel dimethylamino-substituted alkynylamidinate anions of the composition [Me₂N−CH₂−C≡C−C(NR)₂]⁻ (R = ⁱPr, cyclohexyl (Cy)). The unsolvated lithium derivatives Li[Me₂N−CH₂−C≡C−C(NR)₂] ( 1 : R = ⁱPr, 2 : R = Cy) were obtained in good yields by treatment of in situ-prepared Me₂N−CH₂−C≡C−Li with the respective carbodiimides, R−N=C=N−R. Recrystallization of 1 and 2 from THF afforded the crystalline THF adducts Li[Me₂N−CH₂−C≡C−C(NR)₂] ⋅ nTHF ( 1 a : R = ⁱPr, n=1; 2 a : R = Cy, n=1.5). Precursor 2 was subsequently used to study initial complexation reactions with selected di- and trivalent transition metals. The dark red homoleptic vanadium(III) tris(alkynylamidinate) complex V[Me₂N−CH₂−C≡C−C(NCy)₂]₃ ( 3 ) was prepared by reaction of VCl₃(THF)₃ with 3 equiv. of 2 (75 % yield). A salt-metathesis reaction of 2 with anhydrous FeCl₂ in a molar ratio of 2 : 1 afforded the dinuclear homoleptic iron(II) alkynylamidinate complex Fe₂[Me₂N−CH₂−C≡C−C(NCy)₂]₄ ( 4 ) in 69 % isolated yield. Similarly, treatment of Mo₂(OAc)₄ with 3 or 4 equiv. of 2 provided the dinuclear, heteroleptic molybdenum(II) amidinate complex Mo₂(OAc)[Me₂N−CH₂−C≡C−C(NCy)₂]₃ ( 5 ; yellow crystals, 50 % isolated yield). The cyclohexyl-substituted title compounds 2 a , 4 , and 5 were structurally characterized through single-crystal X-ray diffraction studies.     

Multinuclear Solid‐State Magnetic Resonance as a Sensitive Probe of Structural Changes upon the Occurrence of Halogen Bonding in Co‐crystals

Although the understanding of intermolecular interactions, such as hydrogen bonding, is relatively well‐developed, many additional weak interactions work both in tandem and competitively to stabilize a given crystal structure. Due to a wide array of potential applications, a substantial effort has been invested in understanding the halogen bond. Here, we explore the utility of multinuclear (¹³C, ^14/15N, ¹⁹F, and ¹²⁷I) solid‐state magnetic resonance experiments in characterizing the electronic and structural changes which take place upon the formation of five halogen‐bonded co‐crystalline product materials. Single‐crystal X‐ray diffraction (XRD) structures of three novel co‐crystals which exhibit a 1:1 stoichiometry between decamethonium diiodide (i.e., [(CH₃)₃N⁺(CH₂)₁₀N⁺(CH₃)₃][2 I^?]) and different para‐dihalogen‐substituted benzene moieties (i.e., p‐C₆X₂Y₄, X=Br, I; Y=H, F) are presented. ¹³C and ¹⁵N NMR experiments carried out on these and related systems validate sample purity, but also serve as indirect probes of the formation of a halogen bond in the co‐crystal complexes in the solid state. Long‐range changes in the electronic environment, which manifest through changes in the electric field gradient (EFG) tensor, are quantitatively measured using ¹⁴N NMR spectroscopy, with a systematic decrease in the ¹⁴N quadrupolar coupling constant (C_Q) observed upon halogen bond formation. Attempts at ¹²⁷I solid‐state NMR spectroscopy experiments are presented and variable‐temperature ¹⁹F NMR experiments are used to distinguish between dynamic and static disorder in selected product materials, which could not be conclusively established using solely XRD. Quantum chemical calculations using the gauge‐including projector augmented‐wave (GIPAW) or relativistic zeroth‐order regular approximation (ZORA) density functional theory (DFT) approaches complement the experimental NMR measurements and provide theoretical corroboration for the changes in NMR parameters observed upon the formation of a halogen bond.     

Outer‐Sphere 2 e−/2 H+ Transfer Reactions of Ruthenium(II)‐Amine and Ruthenium(IV)‐Amido Complexes

A diverse set of 2 e⁻/2 H⁺ reactions are described that interconvert [Ru^II(bpy)(en*)₂]²⁺ and [Ru^IV(bpy)(en‐H*)₂]²⁺ (bpy=2,2′‐bipyridine, en*=H₂NCMe₂CMe₂NH₂, en*‐H=H₂NCMe₂CMe₂NH⁻), forming or cleaving different O−H, N−H, S−H, and C−H bonds. The reactions involve quinones, hydrazines, thiols, and 1,3‐cyclohexadiene. These proton‐coupled electron transfer reactions occur without substrate binding to the ruthenium center, but instead with precursor complex formation by hydrogen bonding. The free energies of the reactions vary over more than 90 kcal mol⁻¹, but the rates are more dependent on the type of X−H bond involved than the associated ΔG °. There is a kinetic preference for substrates that have the transferring hydrogen atoms in close proximity, such as ortho ‐tetrachlorobenzoquinone over its para ‐isomer and 1,3‐cyclohexadiene over its 1,4‐isomer, perhaps hinting at the potential for concerted 2 e⁻/2 H⁺ transfers.     

Mutual enhancing effects of the σ-hole interactions and halogen/hydrogen-bonded interactions in the iodine-ylide containing complexes

The region of positive electrostatic potentials (σ-hole) has been found along the extension of the C–I bond in the iodine-ylide CH₂IH, which suggests that the iodine-ylide could interact with nucleophiles to form weak, directional noncovalent interactions. MP2 calculations confirmed that the I···N σ-hole interaction exists in the CH₂IH···NCX (X = H, F, Cl, Br, I) bimolecular complexes. The NCCl···CH₂IH···NCX (X = H, F, Cl, Br, I) termolecular complexes were constructed to investigate the weakly bonded σ-hole interactions to be strengthened by Cl···C halogen bond. And then, the NCY···CH₂IH···NCCl (Y = H, F, Cl, Br, I) termolecular complexes were designed to investigate the enhancing effects of the I···N σ-hole interaction on the Y···C halogen/hydrogen-bonded interactions. Accompany with the mutual enhancing processes of the σ-hole interactions and halogen/hydrogen-bonded interactions in the iodine-ylide containing termolecular complexes, both the I···N σ-hole interactions and Y···C halogen/hydrogen-bonded interactions become more polarizable.     

The Influence of Secondary Interactions on the [N−I−N]+ Halogen Bond

[Bis(pyridine)iodine(I)]⁺ complexes offer controlled access to halonium ions under mild conditions. The reactivity of such stabilized halonium ions is primarily determined by their three-center, four-electron [N−I−N]⁺ halogen bond. We studied the importance of chelation, strain, steric hindrance and electrostatic interaction for the structure and reactivity of halogen bonded halonium ions by acquiring their ¹⁵N NMR coordination shifts and measuring their iodenium release rates, and interpreted the data with the support of DFT computations. A bidentate ligand stabilizes the [N−I−N]⁺ halogen bond, decreasing the halenium transfer rate. Strain weakens the bond and accordingly increases the release rate. Remote modifications in the backbone do not influence the stability as long as the effect is entirely steric. Incorporating an electron-rich moiety close by the [N−I−N]⁺ motif increases the iodenium release rate. The analysis of the iodine(I) transfer mechanism highlights the impact of secondary interactions, and may provide a handle on the induction of stereoselectivity in electrophilic halogenations.