E2/S_(N)2 Selectivity Driven by Reaction Dynamics. Insight into Halogen Bonding

Ubiquitous competition of stereospecific E2 elimination versus SN2 substitution is of central importance in chemical synthesis.Herein,we uncover how the nature of the leaving group affects the intrinsic competing dynamics that remains largely unknown as opposed to its role in reactivity.Results are presented for a prototype case of fluoride anion reacting with ethyl chloride,compared to reacting with ethyl iodide.Chemical dynamics simulations reproduce scattering signatures observed in experiments and reveal that the direct stripping/rebound mechanisms characterize the E2/S_(N)2 reactions,in line with their dynamic fingerprints identified.Quite similar structures and energetics are found for the Cl^(−)and I^(−)leaving halides,whereas the competing dynamics show markedly distinct features.A halogen-bonding attraction is found to be crucial that modifies the interaction potential in the entrance channel and essentially tunes the underlying atomistic behaviors causing a mechanistic shift.This work highlights the dynamical effects induced by a leaving group on the proceedings of baseinduced elimination and nucleophilic substitution,providing a unique insight into the reaction selectivity for complex chemical networks and environments.

Halogen Bonding： An AIM Analysis of the Weak Interactions

A series of complexes formed between halogen-containing molecules and ammonia have been investigated by means of the atoms in molecules （AIM） approach to gain a deeper insight into halogen bonding. The existence of the halogen bond critical points （XBCP） and the values of the electron density （Pb） and Laplacian of electron density （V2pb） at the XBCP reveal the closed-shell interactions in these complexes. Integrated atomic properties such as charge, energy, polarization moment, volume of the halogen bond donor atoms, and the corresponding changes （△） upon complexation have been calculated. The present calculations have demonstrated that the halogen bond represents different AIM properties as compared to the well-documented hydrogen bond. Both the electron density and the Laplacian of electron density at the XBCP have been shown to correlate well with the interaction energy, which indicates that the topological parameters at the XBCP can be treated as a good measure of the halogen bond strength In addition, an excellent linear relationship between the interatomic distance d（X…N） and the logarithm of Pb has been established.

The role of halogen bonding in improving OFET performance of a naphthalenediimide derivative

Controlling microstructure and thin film morphology of organic semiconductors by supramolecular arrangement is critical to improving their device performance. To realize well-controlling supramolecular assembly, a core-expanded naphthalene diimides derivative （1） was designed and synthesized as an n-type organic semiconductor and also as a halogen bonding （XB） donor that could form complementary XBs with 2,2-dipyridine or 2,2-bipyrimidine acceptor. The XB interactions in the solid state of 1/2,2- dipyridine and 1/2,2-bipyrimidine were confirmed by a series of characterization methods, such as thermal gravimetric analysis （TGA）, X-ray photoelectron spectroscopy （XPS）, nuclear magnetic resonance （NMR） involving 13F NMR and solid-state 13C NMR. Organic field-effect transistors （OFETs） based on XB complexes 1/2,2-dipyridine or 1/2,2-bipyrimidine showed better device performance than that of devices based on pure 1, with the average electron mobility increased more than doubled （from 0.027cm2V-1 s-1 to 0.070cm2V-1 s-1）.

Co-existing Intermolecular Halogen Bonding and Hydrogen Bonding in the Compound Trans-5,10-bis(1-bromodifluoro- acetyl-1-ethoxycarbonyl-methylidene)thianthrene

Trans-5,10-bis(1-bromodifluoroacetyl-1-ethoxycarbonyl-methylidene)thianthrene (1b) was prepared from the reaction of BrCF2COC(N2)CO2Et with thianthrene. X-ray single crystal diffraction analysis showed that the inter-molecular halogen bonding and hydrogen bonding coexisted in this compound. The bromine atom acted as an elec-tron acceptor in the halogen bond and an electron donor in the hydrogen bond. It is the first example that the bro-mine atom acted as such a dual role in the hydrogen and halogen bond.

Ab Initio Calculations on Halogen Bond Between N—Br and Electron-donating Groups

Ab initio calculations of complexes formed between N-bromosuccinimide and a series of electron-donating groups were performed at the level of MP2/Lanl2DZ^＊ to gain a deeper insight into the nature of the N--Br halogen bonding. For the small complexes, H3 C--Br… NH3 and H2 N--Br…NH3 , the primary calculation has demonstrated that the N--Br in H2 N--Br… NH3 can form a much stronger halogen-bonding complex than the C--Br. A comparison of neutral hydrogen bond complex series reveals that the electron-donating capacities of the atoms decrease in the order, N 〉 O 〉 S; 0 （ sp^3 ） 〉 0 （ sp^2 ）, which is adequate for the C--Br halogen bonding. Interaction energies, in conjunction with the geometrical parameters show that the affinitive capacity of trihalide anions X^-3 with N-bromosuccinimide are markedly lower than that of the corresponding X^- with N-bromosuccinimide, even lower than those of neutral molecules with N-bromosueeinimide. AIM analyses further eorffirmed the above results.

Theoretical Study of the Iodine-catalyzed Nucleophilic Addition by Halogen Bond

The iodine-catalyzed nucleophilic addition of pyrrole to acetone has been studied by density functional theory at the level of Lanl2DZ＊. It has been shown that the first iodine molecule appears to have a remarkable catalytic effect on this reaction by halogen bond between carbonyl oxygen and iodine molecule, but the second one does not improve the reaction largely. In general, the nucleophilic addition at the C（2） site of pyrrole is more favorable than that at the C（3） site; however, this trend is not prominent or even changed in acetronitrile solvent for the indole system, which is consistent with the experimental result by Bandgar.

Investigation of Intermolecular C-H···Halogen Hydrogen Bonded Supramolecular Assemblies in Three Copper(Ⅰ) Complexes Formed by 3,3'-Dimethoxy-6,6'-dimethyl-2,2'-bipyridine Ligand

Three new crystalline compounds 1-3 were successfully obtained by the reactions of 3,3＇-dimethoxy-6,6＇-dimethyl-2,2＇-bipyridine ligand（dmbp） with the corresponding Cu（Ⅰ） salts.Crystal data for 1：orthorhombic Pbca,a = 18.5858（12）,b = 8.1821（5）,c = 20.6066（13） ,V = 3133.7（3） 3,Z = 8,Dc = 1.843 g/cm3,F（000） = 1696,μ = 3.366 mm-1,the final R = 0.0223 and wR = 0.0542.Crystal data for 2：Orthorhombic Pbca,a = 18.7883（16）,b = 8.3249（7）,c = 19.0294（17） ,V = 2976.4（4） 3,Z = 8,Dc = 1.731 g/cm3,F（000） = 1552,μ = 4.154 mm-1,the final R = 0.0279 and wR = 0.0680.Crystal data for 3：monoclinic P21/c,a = 13.812（10）,b = 9.910（7）,c = 23.444（17） ,β = 104.3350（10）°,V = 3090（4） 3,Z = 4,Dc = 1.476 g/cm3,F（000） = 1408,μ = 1.588 mm-1,the final R = 0.0479 and wR = 0.1081.The results of X-ray crystallographic analysis revealed that C14H16ICuN2O2（1） and C14H16BrCuN2O2（2） are isostructural compounds with the dimers connected by C-H···halogen hydrogen bonds to generate a three-dimensional（3D） supramolecular network in 1 and a two-dimensional（2D） sheet structure in 2,respectively,while the mononuclear complex C28H32Cl2Cu2N4O4（3） is ionic.In 3,the [Cu（dmbp）2]＋ cations and [ClCuCl]-anions are connected by C-H···Cl hydrogen bonds to form a one-dimensional（1D） chain along the a axis.Therefore,in the three complexes,the C-H···halogen hydrogen bonds dominate their crystal structures.Additionally,The UV luminescent properties of complexes 1-3 were investigated.

Investigation of the Substituent Effects on π-Type Pnicogen Bond Interaction

Intermolecular interactions between PH2Cl and Ar–R（R = H,OH,NH2,CH3,Br,Cl,F,CN,NO2） were calculated by using MP2/aug-cc-p VDZ quantum chemical method.It has been shown from our calculations that the aromatic rings with electron-withdrawing groups represent much weaker binding affinities than those with electron-donating groups.The charge-transfer interaction between PH2Cl and Ar–R plays an important role in the formation of pnicogen bond complexes,as revealed by NBO analysis.Nevertheless,AIM analysis shows that the nature of the interactions between PH2Cl and Ar–R is electrostatic,and the interaction energies of the complexes are correlated positively with the electron densities in the bond critical points（BCPs）.RDG/ELF graphical analyses were performed to visualize the positions and strengths of the pnicogen bonding,as well as the spatial change of the electron localization upon the formation of complexes.The π-type halogen bond was also calculated,and it has been revealed that the π-type pnicogen bond systems are more stable than the halogen bond ones.

Theoretical Studies on the Iodine-catalyzed Nucleophilic Addition of Acetone with Five-membered Heterocycles

The iodine-catalyzed nucleophilic addition reactions of pyrrole, furan, or thiophene with acetone were studied in gas and solvent by the density functional theory at the level of Lanl2DZ^＊. It was seen that the halogen bond between iodine and carbonyl oxygen appeared to have an important catalytic effect on such reactions, and the first iodine molecule maximally diminished the barrier height by 41 kJ/mol, while the second iodine molecule could not improve such reactions largely. It was concluded that the C2-addition was generally more favorable than the C3-addition for the three heterocycles; however, iodine considerably more effectively catalyzed the C3-addition than the C2-addition for pyrrole. It was also revealed by PCM calculation that the iodine-catalyzed nucleophilic additions occurred more easily in solvent than in gas, which explained the experiment performed by Bandgar et al..

Electrophilic Halogen Reagents-mediated Halogenation: Synthesis of Halogenated Dihydro-1,3-oxazine Derivatives

Halogenation of N-cinnamylbenzamides and N-[(2H-chromen-3-yl)methyl]benzamides using electrophilic halogen source was reported.Various halogenated dihydro-1,3-oxazine derivatives(45 examples)were synthesized in high to excellent yields(up to 98%yields),as well as halogenated dihydrochromeno-1,3-oxazine derivatives(56 examples,up to 96%yields).The properties of mild conditions,metal-free and high efficiency of the reaction made it a promising strategy in future applications for the construction of carbon-halogen(fluorine,F;chlorine,Cl;bromine,Br;iodine,I)bond and 1,3-oxazine derivatives.

Chiral supramolecular 2D halogen-bonded organic frameworks constructed by post-synthetic modified cross-linking strategy

The development of preparation methods for XOFs,as a new class of organic frameworks,plays a crucial role in shaping their structures,functions,and potential applications.In this study,we presented the construction of chiral supramolecular 2D halogen-bonded organic frameworks(XOFs)through a post-synthetic modification strategy.A linear halogen-bonded organic polymer(XOP),XOP-DPBA,decorated with aldehyde groups,was initially prepared to validate the feasibility of post-synthetic modification for XOF construction and functionalization.XOP-DPBA exhibited excellent reactivity with amines,forming imine bonds.By utilizing this reactivity,a series of cross-linked 2D XOFs were efficiently prepared through post-synthetic modified cross-linking reactions.Furthermore,we successfully introduced chiralα/β-cyclodextrins(α/β-CD)into the XOF skeletons via host-guest interactions,resulting in the fabrication of chiral supramolecular 2D XOFs.These chiral XOFs displayed the induced circular dichroism(ICD)signals and assembled them into helical fibers.The post-synthetic modification strategy demonstrated its versatility and simplicity for the construction and functionalization of XOFs.

Halogen-bonded Cocrystal Based on Tetrathiafulvalene Derivatives

In this paper, two cocrystals 1 and 2 with the same chemical composition [L1.L2 ](L1 = bis(4’-pyridyl)-TTF, L2 = 4,4’-diiodophenyl) were synthesized by slow diffusion with different solvent systems. Cocrystals 1 and 2 were characterized by single-crystal X-ray and the purity of these two cocrystals was confirmed by PXRD data. The photocurrent responses of these two cocrystals were also tested. Only cocrystal 1 could generate photocurrent signal when exposed to light. From the crystal structure analysis, the possible reason may come from the different biphenyl conformations in L2.

Halogen Bond Catalysis on Carbonyl-Olefin Ring-Closing Metathesis Reaction:Comparison with Lewis Acid Catalysis

The carbonyl-olefin ring-closing metathesis reactions have become a powerful tool for carbon-carbon bond formation.In this work,the halogen bond catalysis and classical Lewis acid catalysis on the carbonyl-olefin ring-closing metathesis reaction were investigated by density function theory.For both the halogen bond catalysis and classical Lewis acid catalysis,the carbonyl-olefin ring-closing me-tathesis reaction occurs by[2+2]-cycloaddition process and[2+2]-cycloreversion process,the reaction energy barriers are low,there-fore,it can be performed easily at room temperature.The essential difference of the two kinds of catalysts is that the catalytic mecha-nism of halogen bond catalysis is mainly contribution of electrostatic interaction,while that of classical Lewis acid catalysis is mainly catalyzed by orbital interaction.The halogen bond donor catalysts(ICI_(3),IF_(3))are expected to be efficient catalysts for the reaction and further promote the chemical synthesis of carbonyl-olefin ring-closing metathesis reaction.

Cocrystal Assembled by 1,2-Diiodotetrafluorobenzene and Acridine via C-I…N Halogen Bond and π-hole…F Bonds

The concepts on o-hole and ^-hole bonds are suggested. A cocrystal with repeated 8-F-atom unit as basic struc- tural motif is assembled based on bifurcated C-I…N…I-C halogen/σ-hole bond and antiparallel double π-hole… F bonds by 1,2-diiodotetrafluorobenzene and acridine and characterized well by XRD, powder XRD and solid 19F NMR, etc. Also the calculated interaction energies are -26.8 and -31.5 kJ/mol for bifurcated C-I…N sp……2 halogen bonds, and -14.3 kJ/mol for a pair of n-hole…F bonds. In this system C-I…N halogen bond has stronger competitive ability to C-I…π halogen bond due to stronger basicity of N than π-system in acridine. The combination of the halogen/σ-hole and π-hole bonds or together with other weak interactions could play a key role in assembling function materials, molecular recognition and design of drugs and so on.

Novel 1,2,3-triazole-based compounds： Iodo effect on their gelation behavior and cation response

Two new series of 1,2,3-triazole derivatives, with and without iodo substitution, were synthesized and their gelation properties were measured. It was found that the iodo substitution at position 5 of triazole ring could greatly enhance the gelation ability. Scanning electron microscopy and X-ray diffraction reveal that the structures of the organogels from iodo and hydrogenous gelators are totally different, lodo gels are selectively responsive to the stimuli of Hg2＋, whereas hydrogenous gels can respond to Hg2＋ and Cu2＋. Moreover, the reversible gel-sol transition of hydrogenous gels can be controlled by redox reaction or tuned with suitable chemicals. The single crystal analysis of reference compound （C2） suggests that there are intermolecular and intramolecular non-classical hydrogen bonding interactions but no π-π interaction in hydrogenous gelator. The great difference between the two series of compounds results from the iodo effect and implies the existence of halogen bonding interaction in the iodo compounds.

Temperature dependences of electric properties of tetramethylammonium mono-and pentaiodide

The dielectric properties of tetramethylammonium monoiodide and pentaiodide were investigated in broad temperature range(-150℃till+50℃).It was demonstrated that the structural organization of the polyiodide chain containing I...I charge-assisted halogen bonds influenced the parameters and the mechanism of electric conductivity of considered compound.The impedance spectroscopic measurements revealed that the direct current electric conductivity of pentaiodide salt is around four orders of magnitude higher than that of corresponding monoiodide.Moreover,pentaiodide demonstrates the hopping mechanism of conductivity.

Structural Study on Four co-Crystals of N-Containing Heteroaromatics with Iodofluorobenzene

N-Containing heteroaromatics 1,2,4,5-tetra（pyridin-3-yl）benzene[1,2,4,5-T（3-PY）B] and 1,2,4,5-tetra（pyridin-4-yl）benzene[1,2,4,5-T（4-PY）B] were each co-crystallized with 1,2-diiodo-tetrafluoro-benzene（1,2-DITFB）, or 1,4-diiodo-tetrafluoro-benzene（1,4-DITFB）, respectively, generating four co-crystals, namely, （1,2-DITFB）4 [1,2,4,5-T（3-PY）B]（1）, （1,2-DITFB）4.[ 1,2,4,5-T（4-PY）B]（2）, （1,4-DITFB）2.[1,2,4,5-T（3-PY）B]-CHCI3（3）, and （1,4-DITFB）-[1,2,4,5-T（4-PY）B]2CHCI3（4）. This study takes aim at providing an insight into the relative importance of fundamental solid state halogen bonding interactions（i.e., halogen..N, halogen,..halogen, and halogen...π in systems. The effects of the donor and acceptor on supramolecular assembly and the crystal structure determined interactions were discussed. The N...I halogen bonds are the main directing interactions responsible for the observed structures. In compounds 1 and 2, the donors exhibited lower-than-expected supramolecular connectivity. In spite of this, co-crystal 2 exhibits polymeric structures consisting of infinite one-dimensional（1D） double-zigzag chains of alternating electron donor and acceptor. The basic structure of co-crystals 3 and 4 is also infinite 1D chain. Therefore, the ID halogen bonded supramolecular assemblies can be obtained by matching the appropriate donor and acceptor.

Building up 1-D, 2-D, and 3-D Polyiodide Frameworks by Finely Tuning the Size of Aryls on Ar-S-TTF in the Charge-Transfer （CT） Complexes of Ar-S-TTFs and Iodine

The arylthio-substituted tetrathiafuivalenes （Ar-S-TTFs） are electron donors having three reversible states, neutral, cation radical, and dica- tion. The charge-transfer （CT） between Ar-S-TTFs （TTF1--TTF3） and iodine （12） is reported herein. TTF1--TTF3 show the CT with 12 in the CH2C12 solution, but they are not completely converted into cation radical state. In CT complexes of TTF1--TTF3 with 12, the charged states of Ar-S-TTFs are distinct from those in solution. TTF1 is at cation radical state, and TTF2--TTF3 are oxidized to dication. The iodine components in complexes show various structures including 1-D chain of V-shaped （Is）-, and 2-D and 3-D iodine networks composed of 12 and （13）^- .