scholarly journals Catalytic Activation via π –Backbonding in Halogen Bonds?

2020 ◽  
Author(s):  
Andrew Wang ◽  
Pierre Kennepohl
Keyword(s):  
Halogen Bond ◽  
Halogen Bonding ◽  
Lewis Base ◽  
Computational Studies ◽  
Halogen Bonds ◽  
Covalent Interaction ◽  
Lewis Bases ◽  
Chemical Catalysis ◽  
Catalytic Activation

The role of halogen bonding (XB) in chemical catalysis has largely involved using XB donors as Lewis acid activators to modulate the reactivity of partner Lewis bases. We explore a more uncommon scenario, where a Lewis base modulates reactivity via a spectator halogen bond interaction. Our computational studies reveal that spectator halogen bonds may play an important role in modulating the rate of S<sub>N</sub>2 reactions. Most notably, π acceptors such as PF<sub>3</sub> significantly decrease the barrier to subsitution by decreasing electron density in the very electron rich transition state. Such π-backbonding represents an example of a heretofor unexplored situation in halogen bonding: the combination of both s-donation and π-backdonation in this “non-covalent” interaction.

scholarly journals Catalytic Activation via π –Backbonding in Halogen Bonds?

2020 ◽  
Author(s):  
Andrew Wang ◽  
Pierre Kennepohl
Keyword(s):  
Halogen Bond ◽  
Halogen Bonding ◽  
Lewis Base ◽  
Computational Studies ◽  
Halogen Bonds ◽  
Covalent Interaction ◽  
Lewis Bases ◽  
Chemical Catalysis ◽  
Catalytic Activation

The role of halogen bonding (XB) in chemical catalysis has largely involved using XB donors as Lewis acid activators to modulate the reactivity of partner Lewis bases. We explore a more uncommon scenario, where a Lewis base modulates reactivity via a spectator halogen bond interaction. Our computational studies reveal that spectator halogen bonds may play an important role in modulating the rate of S<sub>N</sub>2 reactions. Most notably, π acceptors such as PF<sub>3</sub> significantly decrease the barrier to subsitution by decreasing electron density in the very electron rich transition state. Such π-backbonding represents an example of a heretofor unexplored situation in halogen bonding: the combination of both s-donation and π-backdonation in this “non-covalent” interaction.

scholarly journals Activation of a Metal-Halogen Bond by Halogen Bonding

2020 ◽  
Author(s):  
Stefan Huber ◽  
Julian Wolf ◽  
Florian Huber ◽  
Nikita Erochok ◽  
Flemming Heinen ◽  
...  
Keyword(s):  
Halogen Bond ◽  
Halogen Bonding ◽  
Gold Catalysis ◽  
Halogen Bonds ◽  
Covalent Interaction ◽  
Lewis Acidic Sites ◽  
Test Reactions ◽  
Acidic Sites ◽  
Elemental Iodine

In recent years, the non-covalent interaction of halogen bonding (XB) has found increasing application in organocatalysis. However, reports of the activation of metal-ligand bonds by XB have so far been limited to a few reactions with elemental iodine or bromine. Herein, we present the activation of metal-halogen bonds by two classes of inert halogen bond donors and the use of the resulting activated complexes in homogenous gold catalysis. The only recently explored class of iodolium derivatives were shown to be effective activators in two test reactions and their activity could be modulated by blocking of the Lewis acidic sites. Bis(benzimidazolium)-based halogen bonding activators provided even more rapid conversion, while the non-iodinated reference compound showed little activity. The role of halogen bonding in the activation of metal-halogen bonds was further investigated by NMR experiments and DFT calculations, which support the mode of activation occurring via halogen bonding.

scholarly journals Activation of a Metal-Halogen Bond by Halogen Bonding

2020 ◽  
Author(s):  
Stefan Huber ◽  
Julian Wolf ◽  
Florian Huber ◽  
Nikita Erochok ◽  
Flemming Heinen ◽  
...  
Keyword(s):  
Halogen Bond ◽  
Halogen Bonding ◽  
Gold Catalysis ◽  
Halogen Bonds ◽  
Covalent Interaction ◽  
Lewis Acidic Sites ◽  
Test Reactions ◽  
Acidic Sites ◽  
Elemental Iodine

In recent years, the non-covalent interaction of halogen bonding (XB) has found increasing application in organocatalysis. However, reports of the activation of metal-ligand bonds by XB have so far been limited to a few reactions with elemental iodine or bromine. Herein, we present the activation of metal-halogen bonds by two classes of inert halogen bond donors and the use of the resulting activated complexes in homogenous gold catalysis. The only recently explored class of iodolium derivatives were shown to be effective activators in two test reactions and their activity could be modulated by blocking of the Lewis acidic sites. Bis(benzimidazolium)-based halogen bonding activators provided even more rapid conversion, while the non-iodinated reference compound showed little activity. The role of halogen bonding in the activation of metal-halogen bonds was further investigated by NMR experiments and DFT calculations, which support the mode of activation occurring via halogen bonding.

1,3,5-Tri(iodoethynyl)-2,4,6-trifluorobenzene: halogen-bonded frameworks and NMR spectroscopic analysis

2017 ◽  
Vol 73 (2) ◽  
pp. 153-162 ◽  
Author(s):  
Patrick M. J. Szell ◽  
Bulat Gabidullin ◽  
David L. Bryce
Keyword(s):  
Solid State ◽  
Crystal Engineering ◽  
Halogen Bond ◽  
Halogen Bonding ◽  
Lewis Base ◽  
Phosphonium Salts ◽  
Covalent Interaction ◽  
Framework Materials ◽  
Engineering Strategy ◽  
Triphenylphosphonium Bromide

Halogen bonding is the non-covalent interaction between the region of positive electrostatic potential associated with a covalently bonded halogen atom, named the σ-hole, and a Lewis base. Single-crystal X-ray diffraction structures are reported for a series of seven halogen-bonded cocrystals featuring 1,3,5-tris(iodoethynyl)-2,4,6-trifluorobenzene (1) as the halogen-bond donor, and bromide ions (as ammonium or phosphonium salts) as the halogen-bond acceptors: (1)·MePh3PBr, (1)·EtPh3PBr, (1)·acetonyl-Ph3PBr, (1)·Ph4PBr, (1)·[bis(4-fluorophenyl)methyl]triphenylphosphonium bromide, and two new polymorphs of (1)·Et3BuNBr. The cocrystals all feature moderately strong iodine–bromide halogen bonds. The crystal structure of pure [bis(4-fluorophenyl)methyl]triphenylphosphonium bromide is also reported. The results of a crystal engineering strategy of varying the size of the counter-cation are explored, and the features of the resulting framework materials are discussed. Given the potential utility of (1) in future crystal engineering applications, detailed NMR analyses (in solution and in the solid state) of this halogen-bond donor are also presented. In solution, complex13C and19F multiplets are explained by considering the delicate interplay between variousJcouplings and subtle isotope shifts. In the solid state, the formation of (1)·Et3BuNBr is shown through significant13C chemical shift changes relative to pure solid 1,3,5-tris(iodoethynyl)-2,4,6-trifluorobenzene.

The15N NMR chemical shift in the characterization of weak halogen bonding in solution

2017 ◽  
Vol 203 ◽  
pp. 333-346 ◽  
Author(s):  
Sebastiaan B. Hakkert ◽  
Jürgen Gräfenstein ◽  
Mate Erdelyi
Keyword(s):  
Hydrogen Bond ◽  
Chemical Shift ◽  
Halogen Bond ◽  
Molar Fraction ◽  
Halogen Bonding ◽  
Relative Strength ◽  
Lewis Base ◽  
Halogen Bonds ◽  
Bonded Complexes

We have studied the applicability of15N NMR spectroscopy in the characterization of the very weak halogen bonds of nonfluorinated halogen bond donors with a nitrogenous Lewis base in solution. The ability of the technique to detect the relative strength of iodine-, bromine- and chlorine-centered halogen bonds, as well as solvent and substituent effects was evaluated. Whereas computations on the DFT level indicate that15N NMR chemical shifts reflect the diamagnetic deshielding associated with the formation of a weak halogen bond, the experimentally observed chemical shift differences were on the edge of detectability due to the low molar fraction of halogen-bonded complexes in solution. The formation of the analogous yet stronger hydrogen bond of phenols have induced approximately ten times larger chemical shift changes, and could be detected and correlated to the electronic properties of substituents of the hydrogen bond donors. Overall,15N NMR is shown to be a suitable tool for the characterization of comparably strong secondary interactions in solution, but not sufficiently accurate for the detection of the formation of thermodynamically labile, weak halogen bonded complexes.

scholarly journals Role of Halogen Substituents on Halogen Bonding in 4,5-DiBromohexahydro-3a,6-Epoxyisoindol-1(4H)-ones

Crystals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 112
Author(s):  
Atash V. Gurbanov ◽  
Dmitriy F. Mertsalov ◽  
Fedor I. Zubkov ◽  
Maryana A. Nadirova ◽  
Eugeniya V. Nikitina ◽  
...  
Keyword(s):  
Hydrogen Bonds ◽  
Halogen Bond ◽  
Halogen Bonding ◽  
Halogen Bonds ◽  
Intermolecular Hydrogen Bonds ◽  
3D Structures ◽  
Supramolecular Architectures

A series of 4,5-dibromo-2-(4-substituted phenyl)hexahydro-3a,6-epoxyisoindol-1(4H)-ones were synthesized by reaction of the corresponding 2-(4-substituted phenyl)-2,3,7,7a-tetrahydro-3a,6-epoxyisoindol-1(6H)-ones with [(Me2NCOMe)2H]Br3 in dry chloroform under reflux for 3−5 h. In contrast to the 4-F and 4-Cl substituents, one of the bromine atoms of the isoindole moiety behaves as a halogen bond donor in the formation of intermolecular halogen bonding in the 4-H, 4-Br and 4-I analogues. Not only intermolecular hydrogen bonds, but also Ha⋯Ha and Ha⋯π types of halogen bonds in the 4-H, 4-Br, and 4-I compounds, contribute to the formation of supramolecular architectures leading to 2D or 3D structures.

scholarly journals Halogen Bonding: An Underestimated Player in Membrane–drug Interactions

2020 ◽  
Author(s):  
Rafael Nunes ◽  
Diogo Vila Viçosa ◽  
Paulo J. Costa
Keyword(s):  
Drug Discovery ◽  
Chemical Space ◽  
Noncovalent Interactions ◽  
Halogen Bonding ◽  
Lewis Bases ◽  
Protein Ligand Interactions ◽  
Biochemical Systems ◽  
Ligand Interactions ◽  
Dynamics Simulations

<div>Halogen bonds (HaBs) are noncovalent interactions where halogen atoms act as electrophilic species interacting with Lewis bases. These interactions are relevant in biochemical systems being increasingly explored in drug discovery, mainly to modulate protein–ligand interactions. In this work, we report evidence for the existence of HaB-mediated halogen–phospholipid recognition phenomena as our molecular dynamics simulations support the existence of favorable interactions between halobenzene derivatives and both phosphate (PO) or ester (CO) oxygen acceptors from model phospholipid bilayers, thus providing insights into the role of HaBs in driving the permeation of halogenated drug like molecules across biological membranes. This represents a relevant molecular mechanism, previously overlooked, determining the pharmacological activity of halogenated molecules with implications in drug discovery and development, a place where halogenated molecules account for a significant part of the chemical space. Our data also shows that, as the ubiquitous hydrogen bond, HaBs should be accounted for in the development of membrane permeability models.</div>

scholarly journals Halogen-Bonded Guanine Base Pairs, Quartets and Ribbons

2020 ◽  
Vol 21 (18) ◽  
pp. 6571
Author(s):  
Nicholas J. Thornton ◽  
Tanja van Mourik
Keyword(s):  
Base Pair ◽  
Halogen Bond ◽  
Halogen Bonding ◽  
Dna Bases ◽  
Halogen Bonds ◽  
Base Pairs ◽  
Rich Diversity ◽  
Different Types ◽  
Guanine Base ◽  
The Stability

Halogen bonding is studied in different structures consisting of halogenated guanine DNA bases, including the Hoogsteen guanine–guanine base pair, two different types of guanine ribbons (R-I and R-II) consisting of two or three monomers, and guanine quartets. In the halogenated base pairs (except the Cl-base pair, which has a very non-planar structure with no halogen bonds) and R-I ribbons (except the At trimer), the potential N-X•••O interaction is sacrificed to optimise the N-X•••N halogen bond. In the At trimer, the astatines originally bonded to N1 in the halogen bond donating guanines have moved to the adjacent O6 atom, enabling O-At•••N, N-At•••O, and N-At•••At halogen bonds. The brominated and chlorinated R-II trimers contain two N-X•••N and two N-X•••O halogen bonds, whereas in the iodinated and astatinated trimers, one of the N-X•••N halogen bonds is lost. The corresponding R-II dimers keep the same halogen bond patterns. The G-quartets display a rich diversity of symmetries and halogen bond patterns, including N-X•••N, N-X•••O, N-X•••X, O-X•••X, and O-X•••O halogen bonds (the latter two facilitated by the transfer of halogens from N1 to O6). In general, halogenation decreases the stability of the structures. However, the stability increases with the increasing atomic number of the halogen, and the At-doped R-I trimer and the three most stable At-doped quartets are more stable than their hydrogenated counterparts. Significant deviations from linearity are found for some of the halogen bonds (with halogen bond angles around 150°).

scholarly journals Halogen bonding, chalcogen bonding, pnictogen bonding, tetrel bonding: origins, current status and discussion

2017 ◽  
Vol 203 ◽  
pp. 485-507 ◽  
Author(s):  
Lee Brammer
Keyword(s):  
Solid State ◽  
Halogen Bond ◽  
Halogen Bonding ◽  
Main Group ◽  
Solution Phase ◽  
Current Status ◽  
Solid State Chemistry ◽  
Main Group Elements ◽  
Past Work

The role of the closing lecture in a Faraday Discussion is to summarise the contributions made to the Discussion over the course of the meeting and in so doing capture the main themes that have arisen. This article is based upon my Closing Remarks Lecture at the 203rdFaraday Discussion meeting on Halogen Bonding in Supramolecular and Solid State Chemistry, held in Ottawa, Canada, on 10–12thJuly, 2017. The Discussion included papers on fundamentals and applications of halogen bonding in the solid state and solution phase. Analogous interactions involving main group elements outside group 17 were also examined. In the closing lecture and in this article these contributions have been grouped into the four themes: (a) fundamentals, (b) beyond the halogen bond, (c) characterisation, and (d) applications. The lecture and paper also include a short reflection on past work that has a bearing on the Discussion.

scholarly journals Study of the Halogen Bonding between Pyridine and Perfluoroalkyl Iodide in Solution Phase Using the Combination of FTIR and 19F NMR

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
Briauna Hawthorne ◽  
Haiyan Fan-Hagenstein ◽  
Elizabeth Wood ◽  
Jessica Smith ◽  
Timothy Hanks
Keyword(s):  
Halogen Bond ◽  
Equilibrium Constants ◽  
Binding Constants ◽  
Halogen Bonding ◽  
Blue Shift ◽  
Halogen Bonds ◽  
Perfluoroalkyl Iodide ◽  
Solvent Dependence ◽  
Dilution Experiments ◽  
Stretching Vibrations

Halogen bonding between pyridine and heptafluoro-2-iodopropane (iso-C3F7I)/heptafluoro-1-iodopropane (1-C3F7I) was studied using a combination of FTIR and 19F NMR. The ring breathing vibration of pyridine underwent a blue shift upon the formation of halogen bonds with both iso-C3F7I and 1-C3F7I. The magnitudes of the shifts and the equilibrium constants for the halogen-bonded complex formation were found to depend not only on the structure of the halocarbon, but also on the solvent. The halogen bond also affected the Cα-F (C-F bond on the center carbon) bending and stretching vibrations in iso-C3F7I. These spectroscopic effects show some solvent dependence, but more importantly, they suggest the possibility of intermolecular halogen bonding among iso-C3F7I molecules. The systems were also examined by 19F NMR in various solvents (cyclohexane, hexane, chloroform, acetone, and acetonitrile). NMR dilution experiments support the existence of the intermolecular self-halogen bonding in both iso-C3F7I and 1-C3F7I. The binding constants for the pyridine/perfluoroalkyl iodide halogen bonding complexes formed in various solvents were obtained through NMR titration experiments. Quantum chemical calculations were used to support the FTIR and 19F NMR observations.

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