Interplay between halogen bond and lithium bond in MCN-LiCN-XCCH (M = H, Li, and Na; X = Cl, Br, and I) complex: the enhancement of halogen bond by a lithium bond

Quantum chemical calculations have been performed to study the complex of MCN-LiCN-XCCH (M = H, Li, and Na; X = Cl, Br, and I). The aim is to study the cooperative effect between halogen bond and lithium bond. The alkali metal has an enhancing effect on the lithium bond, making it increased by 77 and 94% for the Li and Na, respectively. There is the cooperativity between the lithium bond and halogen bond. The former has a larger enhancing effect on the latter, being in a range of 11.7-29.4%. The effect of cooperativity on the halogen bond is dependent on the type of metal and halogen atoms. The enhancing mechanism has been analyzed in views with the orbital interaction, charge transfer, dipole moment, polarizability, atom charges, and electrostatic potentials. The results show that the electrostatic interaction plays an important role in the enhancement of halogen bond.     

Tetraaryldiborane(4) Can Emit Dual Fluorescence Responding to the Structural Change around the B–B Bond

We report the successful synthesis of tetramesityldiborane(4) (Mes₄B₂) through the reductive coupling of a dimesitylborinium ion. Owing to the steric protection conferred by the mesityl groups, Mes₄B₂ shows exceptional chemical stability and remains intact in water. Single-crystal X-ray analysis revealed that Mes₄B₂ has an orthogonal geometry, where the B–B center is completely hidden by the mesityl groups. Remarkably, Mes₄B₂ emits dual fluorescence at 460 and 620 nm, both in solution and in the solid state. Theoretical calculations showed that Mes₄B₂ in the excited S₁ state adopts a twisted or planar geometry, which is responsible for the shorter- or longer-wavelength fluorescence, respectively. The intensity ratio of the dual fluorescence is sensitive to the viscosity of the medium, which suggests that Mes₄B₂ has potential as a ratiometric viscosity sensor.     

Reaction of B2(o‐tol)4 with CO and Isocyanides: Cleavage of the C≡O Triple Bond and Direct C−H Borylations

The reaction of highly Lewis acidic tetra(o‐tolyl)diborane(4) with CO afforded a mixture of boraindane and boroxine by the cleavage of the C≡O triple bond. ¹³C labeling experiments confirmed that the carbon atom in the boraindane stems from CO. Simultaneously, formation of boroxine 3 could be considered as borylene transfer to capture the oxygen atom from CO. The reaction of diborane(4) with ^tBu?NC afforded an azaallene, while the reaction with Xyl?NC furnished cyclic compounds by direct C?H borylations.     

Competitive interaction between halogen and hydrogen bonds in NH2Br‐HOX (X = F,Cl, and Br) complex

The NH₂Br‐HOX (X = F, Cl, and Br) complexes have been investigated with quantum chemical calculations at the MP2/aug‐cc‐pVTZ level. Five isomers are observed for the Cl and Br complexes, whereas only two isomers are found for the F complex. The geometrical, energetic, and spectroscopic parameters have been analyzed for these complexes. The hydrogen‐bonded complexes are more stable than the halogen‐bonded ones. In most complexes, the associated O? H and O? X bonds are elongated and show a red shift, whereas the distant bonds are contracted and exhibit a blue shift. The complexes have been analyzed with natural bond orbital and atoms in molecules. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Reactivity of a Tetra(o‐tolyl)diborane(4) Dianion as a Diarylboryl Anion Equivalent

Lithium and magnesium salts of tetra(o‐tolyl)diborane(4) dianion, having B=B double bond character, were synthesized. It was clarified that the lithium salt of the dianion has a high‐lying HOMO and a narrow HOMO–LUMO gap, which were perturbed by dissociation of Li⁺ cation, as judged by UV/Vis spectroscopy and DFT calculations. The lithium salt of the dianion reacted as two equivalents of a diarylboryl anion with CH₂Cl₂ or S₈ to give boryl‐substituted products.     

Competition between halogen bond and hydrogen bond in complexes of superalkali Li3S and halogenated acetylene XCCH (X = F,Cl, Br,and I)

Complexes of superalkali Li₃S and XCCH (X = F, Cl, Br, and I) have been studied with theoretical calculations at the MP2/aug‐cc‐pVTZ level. Three types of structures are found: (A) the X atom combines with the S atom through a halogen bond; (B) the X atom interacts with the π electron of Li₃S by a π halogen bond; (C) the H atom combines with the S atom through a hydrogen bond. For A and B, a heavier halogen atom makes the interaction stronger, while for C, the change of interaction energy is not obvious, showing a small dependence on the nature of the X atom in HCCX. A is more stable than B and their difference in stability decreases as X varies from Cl to I. For the F and Cl complexes, A is weaker than C, however, the former is stronger than the latter in the Br and I complexes. The above three types of interactions have been analyzed by means of electron localization function, electron density difference, and energy decomposition, and the results show that they have similar nature and features with conventional interactions. © 2014 Wiley Periodicals, Inc.     

Synthesis,Structure, Bonding,and Reactivity of Metal Complexes Comprising Diborane(4) and Diborene(2): [{Cp*Mo(CO)2}2{μ‐η2:η2‐B2H4}] and [{Cp*M(CO)2}2B2H2M(CO)4], M=Mo,W

The reaction of [(Cp*Mo)₂(μ‐Cl)₂B₂H₆] ( 1 ) with CO at room temperature led to the formation of the highly fluxional species [{Cp*Mo(CO)₂}₂{μ‐η²:η²‐B₂H₄}] ( 2 ). Compound 2, to the best of our knowledge, is the first example of a bimetallic diborane(4) conforming to a singly bridged C_s structure. Theoretical studies show that 2 mimics the Cotton dimolybdenum–alkyne complex [{CpMo(CO)₂}₂C₂H₂]. In an attempt to replace two hydrogen atoms of diborane(4) in 2 with a 2e [W(CO)₄] fragment, [{Cp*Mo(CO)₂}₂ B₂H₂W(CO)₄] ( 3 ) was isolated upon treatment with [W(CO)₅?thf]. Compound 3 shows the intriguing presence of [B₂H₂] with a short B?B length of 1.624(4) Å. We isolated the tungsten analogues of 3 , [{Cp*W(CO)₂}₂B₂H₂W(CO)₄] ( 4 ) and [{Cp*W(CO)₂}₂B₂H₂Mo(CO)₄] ( 5 ), which provided direct proof of the existence of the tungsten analogue of 2 .     

Polysaccharide‐based chiral stationary phases as halogen bond acceptors: A novel strategy for detection of stereoselective σ‐hole bonds in solution

In the last few years, halogen bonds have been exploited in a variety of research areas both in the solid state and in solution. Nevertheless, several factors make formation and detection of halogen bonds in solution challenging. Moreover, to date, few chiral molecules containing electrophilic halogens as recognition sites have been reported. Recently, we described the first series of halogen‐bond‐driven enantioseparations performed on cellulose tris(3,5‐dimethylphenylcarbamate) by high‐performance liquid chromatography. Herein the performances of amylose tris(3,5‐dimethylphenylcarbamate) as halogen bond acceptor were also investigated and compared with respect to cellulose tris(3,5‐dimethylphenylcarbamate). With the aim to explore the effect of polysaccharide backbone on the enantioseparations, the thermodynamic parameters governing the halogen‐dependent enantioseparations on both cellulose and amylose polymers were determined by a study at variable temperature and compared. Molecular dynamics were performed to model the halogen bond in polysaccharide‐analyte complexes. Chiral halogenated 4,4′‐bipyridines were used as test compounds (halogen bond donors). On this basis, a practical method for detection of stereoselective halogen bonds in solution was developed, which is based on the unprecedented use of high‐performance liquid chromatography as technical tool with polysaccharide polymers as molecular probes (halogen bond acceptors). The analytical strategy showed higher sensitivity for the detection of weak halogen bonds.     

Reactions at the B–B Bond of Bis(trisyl)oxadiborirane: Ring Extensions

The B–B bond of bis(trisyl)oxadiborirane OB₂R₂ (R = C(SiMe₃)₃) is opened by amides R′CO(NHR″) to give the dioxaazadiboracyclohexanes [–BR–O–BR–NR″–CHR′–O–] (R′/R″ = H/H, H/Me, H/Et, Me/H: 5 a – d ). The amide MeCO(NHMe) yields 5 e (R′/R″ = Me/Me), when an excess of the amide is applied for 24 h, but yields an isomeric 1 : 1 adduct ( 6 e ), when a stoichiometric amount of the amide is applied for 15 h; upon refluxing this isomer in hexane, it is transformed into 5 e .     

The synthesis of ‘tyrosyl’ peptidomimetics by acid-catalyzed N(1)-C(4) ring opening of 4-(4′-hydroxyphenyl)-azetidine-2-ones

Under acidic conditions, the N(1)-C(4) bond of 4-(4′-hydroxyphenyl)-azetidine-2-ones are cleaved with the formation of a stabilized benzylic carbocation intermediates. The intermediates were reduced by silanes or participated in intramolecular or intermolecular Friedel-Crafts reactions to produce tyrosine mimetics.     

Influence of the halogen and organometallic function in a KCTP (Co)polymerization

The effect of changing the halogen and the organometallic function in a Kumada Catalyst Transfer Polycondensation (KCTP) of poly(3‐alkylthiophene)s (P3AT) is investigated. On the one hand, the bromine substituent is replaced with chlorine in the commonly used 2‐bromo‐5‐chloromagnesio‐3‐hexylthiophene. The effect on the homopolymerization is clear, since the stickiness decreases remarkably, but copolymerizations are hardly affected when a chlorinated monomer is used. Second, the option of changing the organometallic function is considered. Because also organozinc compounds provide a controlled P3AT polymerization with Ni(dppp)Cl₂, but are less reactive than organomagnesium compounds, the effect of using zinc in one monomer during a copolymerization is investigated. However, it is found that the organometallic functions exchange during mixing of the monomers. Consequently, no effect is observed during copolymerizations. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3701–3706     

Evaluating thermodynamic integration performance of the new amber molecular dynamics package and assess potential halogen bonds of enoyl‐ACP reductase (FabI) benzimidazole inhibitors

Thermodynamic integration (TI) can provide accurate binding free energy insights in a lead optimization program, but its high computational expense has limited its usage. In the effort of developing an efficient and accurate TI protocol for FabI inhibitors lead optimization program, we carefully compared TI with different Amber molecular dynamics (MD) engines (sander and pmemd), MD simulation lengths, the number of intermediate states and transformation steps, and the Lennard‐Jones and Coulomb Softcore potentials parameters in the one‐step TI, using eleven benzimidazole inhibitors in complex with Francisella tularensis enoyl acyl reductase (FtFabI). To our knowledge, this is the first study to extensively test the new AMBER MD engine, pmemd, on TI and compare the parameters of the Softcore potentials in the one‐step TI in a protein‐ligand binding system. The best performing model, the one‐step pmemd TI, using 6 intermediate states and 1 ns MD simulations, provides better agreement with experimental results (RMSD = 0.52 kcal/mol) than the best performing implicit solvent method, QM/MM‐GBSA from our previous study (RMSD = 3.00 kcal/mol), while maintaining similar efficiency. Briefly, we show the optimized TI protocol to be highly accurate and affordable for the FtFabI system. This approach can be implemented in a larger scale benzimidazole scaffold lead optimization against FtFabI. Lastly, the TI results here also provide structure‐activity relationship insights, and suggest the parahalogen in benzimidazole compounds might form a weak halogen bond with FabI, which is a well‐known halogen bond favoring enzyme. © 2015 Wiley Periodicals, Inc.     

Theoretical study of the interaction mechanism of single-electron halogen bond complexes H_3C…Br-Y(Y=H,CN,NC,CCH,C_2H_3)

The characteristics and structures of single-electron halogen bond complexes H3C…Br-Y(Y = H,CCH,CN,NC,C2H3) have been investigated by theoretical calculation methods.The geometries were optimized and frequencies calculated at the B3LYP/6-311++G level.The interaction energies were corrected for basis set superposition error(BSSE) and the wavefunctions obtained by the natural bond orbital(NBO) and atom in molecule(AIM) analyses at the MP2/6-311++G level.For each H3C…Br-Y complex,a single-electron Br bond is f...     

Die ersten Bor(III)-di(organosulfonyl)amide: Ein neuartiger B(OS)2N-Sechsring und zwei Aminoboran-Strukturen mit langen B–N-Bindungen

Polysulfonylamines. XCIX. The First Boron(III) Di(organosulfonyl)amides: A Novel B(OS)₂N Six-Membered Ring and Two Aminoborane Structures with Long B–N Bonds Ph₂B[N(SO₂Me)₂] ( 1 ) and the benzo-1,3,2-dioxaboroles C₆H₄O₂BN(SO₂R)₂, where R = Ph ( 2 a ) or Me ( 2 b ), were prepared by treating the appropriate bromoboranes with Me₃SiN(SO₂Me)₂ and/or AgN(SO₂R)₂. Their crystal and molecular structures were determined by low-temperature X-ray diffraction ( 1 : monoclinic, space group P2₁/n; 2 a : monoclinic, P2₁/c; 2 b : triclinic, P 1, structure marred by disorder of one MeSO₂ group). The B atom of 1 features a distorted tetrahedral coordination formed by the ipso-C atoms of the Ph groups and two O atoms of the 1,5-chelating (MeSO₂)₂N⁷ anion (B–O 156.5, 157.7 pm). The resulting six-membered B(OS)₂N ring adopts a boat conformation, B and N lying out of the plane of the other four atoms. In the chelate ligand, which is severely distorted from the common pseudo-C₂ symmetry of the discrete anion, extremely long S–O(B) bonds (151.2, 151.7 pm) are compensated by short N–S bonds (156.1, 156.8 pm). Molecules 2 a and 2 b have aminoborane structures with trigonal-planar coordinations at B and N, unusually long B–N distances suggesting single bonds [ 2 a : 147.6(3), 2 b : 146.3(5) pm], and fairly short N–S bonds ( 2 a : av. 167.4, 2 b : av. 170.4 pm). In 2 a the O₂B plane is twisted by 70.9° vs. the NS₂ plane, whereas the O₂B–NS₂ moiety of 2 b is approximately coplanar (twist-angle ca. 9°).     

Direct through anionic,cationic, and radical active species: Terminal carbon–halogen bond for “controlled”/living polymerizations of styrene

In this work, we examined the synthesis of novel block (co)polymers by mechanistic transformation through anionic, cationic, and radical living polymerizations using terminal carbon–halogen bond as the dormant species. First, the direct halogenation of growing species in the living anionic polymerization of styrene was examined with CCl₄ to form a carbon–halogen terminal, which can be employed as the dormant species for either living cationic or radical polymerization. The mechanistic transformation was then performed from living anionic polymerization into living cationic or radical polymerization using the obtained polymers as the macroinitiator with the SnCl₄/n‐Bu₄NCl or RuCp^*Cl(PPh₃)/Et₃N initiating system, respectively. Finally, the combination of all the polymerizations allowed the synthesis block copolymers including unprecedented gradient block copolymers composed of styrene and p‐methylstyrene. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 465–473