Tribenzotriquinacene Receptors for C60 Fullerene Rotors: Towards C3 Symmetrical Chiral Stators for Unidirectionally Operating Nanoratchets

The synthesis of a stereochemically pure concave tribenzotriquinacene receptor ( 7 ) for C₆₀ fullerene, possessing C₃ point group symmetry, by threefold condensation of C₂‐symmetric 1,2‐diketone synthons ( 5 ) and a hexaaminotribenzotriquinacene core ( 6 ) is described. The chiral diketone was synthesized in a five‐step reaction sequence starting from C_2h‐symmetric 2,6‐di‐tert‐butylanthracene. The highly diastereo‐discriminating Diels–Alder reaction of 2,6‐di‐tert‐butylanthracene with fumaric acid di(?)menthyl ester, catalyzed by aluminium chloride, is the relevant stereochemistry introducing step. The structure of the fullerene receptor was verified by ¹H and ¹³C NMR spectroscopy, mass spectrometry and single crystal X‐ray diffraction. VCD and ECD spectra were recorded, which were corroborated by ab initio DFT calculations, establishing the chiral nature of 7 with about 99.7 % ee, based on the ee (99.9 %) of the chiral synthon ( 1 ). The absolute configuration of 7 could thus be established as all‐S [(2S,7S,16S,21S,30S,35S)‐( 7 )]. Spectroscopic titration experiments reveal that the host forms 1:1 complexes with either pure fullerene (C₆₀) or fullerene derivatives, such as rotor 1′‐(4‐nitrophenyl)‐3′‐(4‐N,N‐dimethylaminophenyl)‐pyrazolino[4′,5′:1,2][60]fullerene ( R ). The complex stability constants of the complexes dissolved in CHCl₃/CS₂ (1:1 vol. %) are K([ C₆₀ ? 7 ])=319(±156) M ^?1 and K([ R ? 7 ])=110(±50) M ^?1. With molecular dynamics simulations using a first‐principles parameterized force field the asymmetry of the rotational potential for [ R ? 7 ] was shown, demonstrating the potential suitability of receptor 7 to act as a stator in a unidirectionally operating nanoratchet.     

Switching the Statistical C3/C1 Ratio in the Threefold Aromatic Substitution of Tribenzotriquinacenes towards the C3 Isomer

Tribenzotriquinacene (TBTQ) is a bowl‐shaped molecule that has been widely used as a molecular building block in supramolecular and materials chemistry. Especially C₃‐symmetric threefold‐substituted TBTQs are interesting for these purposes. Until now a general and selective synthetic approach to those C₃‐symmetric products was lacking, mainly because the typically used electrophilic aromatic substitution reactions of the parent TBTQ hydrocarbons produce predominantly the C₁ isomer over the C₃ isomer (3:1 statistical ratio). Herein we introduce a threefold borylation of TBTQ with the C₃ isomer as the main product (2.6:1 C₃/C₁ ratio). The borylated TBTQ can be converted in good yields into other C₃‐symmetric TBTQs, thus allowing straightforward synthetic access to new building blocks for supramolecular and materials chemistry.     

A Macrocycle Based on a Heptagon‐Containing Hexa‐peri‐hexabenzocoronene

A cyclophane is reported incorporating two units of a heptagon‐containing extended polycyclic aromatic hydrocarbon (PAH) analogue of the hexa‐peri‐hexabenzocoronene (HBC) moiety (hept‐HBC). This cyclophane represents a new class of macrocyclic structures that incorporate for the first time seven‐membered rings within extended PAH frameworks. The saddle curvature of the hept‐HBC macrocycle units induced by the presence of the nonhexagonal ring along with the flexible alkyl linkers generate a cavity with shape complementarity and appropriate size to enable π interactions with fullerenes. Therefore, the cyclophane forms host–guest complexes with C₆₀ and C₇₀ with estimated binding constants of K_a=420±2 m ^?1 and K_a=(6.49±0.23)×10³ m ^?1, respectively. As a result, the macrocycle can selectively bind C₇₀ in the presence of an excess of a mixture of C₆₀ and C₇₀.     

Titanium and Zirconium Complexes with Non‐Salicylaldimine‐Type Imine–Phenoxy Chelate Ligands: Syntheses,Structures, and Ethylene‐Polymerization Behavior

New Ti and Zr complexes that bear imine–phenoxy chelate ligands, [{2,4‐di‐tBu‐6‐(RCH=N)‐C₆H₄O}₂MCl₂] ( 1 : M=Ti, R=Ph; 2 : M=Ti, R=C₆F₅; 3 : M=Zr, R=Ph; 4 : M=Zr, R=C₆F₅), were synthesized and investigated as precatalysts for ethylene polymerization. ¹H NMR spectroscopy suggests that these complexes exist as mixtures of structural isomers. X‐ray crystallographic analysis of the adduct 1 ?HCl reveals that it exists as a zwitterionic complex in which H and Cl are situated in close proximity to one of the imine nitrogen atoms and the central metal, respectively. The X‐ray molecular structure also indicates that one imine phenoxy group with the syn C?N configuration functions as a bidentate ligand, whereas the other, of the anti C?N form, acts as a monodentate phenoxy ligand. Although Zr complexes 3 and 4 with methylaluminoxane (MAO) or [Ph₃C]⁺[B(C₆F₅)₄]^?/AliBu₃ displayed moderate activity, the Ti congeners 1 and 2 , in association with an appropriate activator, catalyzed ethylene polymerization with high efficiency. Upon activation with MAO at 25 °C, 2 displayed a very high activity of 19900 (kg PE) (mol Ti)^?1 h^?1, which is comparable to that for [Cp₂TiCl₂] and [Cp₂ZrCl₂], although increasing the polymerization temperature did result in a marked decrease in activity. Complex 2 contains a C₆F₅ group on the imine nitrogen atom and mediated nonliving‐type polymerization, unlike the corresponding salicylaldimine‐type complex. Conversely, with [Ph₃C]⁺[B(C₆F₅)₄]^?/AliBu₃ activation, 1 exhibited enhanced activity as the temperature was increased (25–75 °C) and maintained very high activity for 60 min at 75 °C (18740 (kg PE) (mol Ti)^?1 h^?1). ¹H NMR spectroscopic studies of the reaction suggest that this thermally robust catalyst system generates an amine–phenoxy complex as the catalytically active species. The combinations 1 /[Ph₃C]⁺[B(C₆F₅)₄]^?/AliBu₃ and 2 /MAO also worked as high‐activity catalysts for the copolymerization of ethylene and propylene.     

Alkali‐Metal Trichloroacetates for Dichloromethylenation of Fullerenes: Nucleophilic Addition‐Substitution Route

The first experimental evidence that fullerenes react with alkali‐metal trichloroacetates through a nucleophilic addition‐substitution route, yielding dichloromethylenefullerenes as the final products, is reported. The intermediates, C₆₀(CCl₃)^? and C₇₀(CCl₃)^? anions, have been isolated in their protonated forms as ortho‐C₆₀(CCl₃)H, as well as three ortho and one para isomer of C₇₀(CCl₃)H. The structures were unambiguously determined by means of ¹H, ¹³C, and ¹H–¹³C HMBC NMR spectroscopy along with UV/Vis spectroscopy. The observed regiochemistry was analyzed with the aid of quantum chemical calculations. Conversion of the protonated compounds into the [6,6]‐closed C_60/70(CCl₂) cycloadducts under basic conditions can be effected only for the ortho isomers, whereas para‐C₇₀(CCl₃)H decomposes back into pristine C₇₀.     

Ion Pairing and Salt Structure in Organic Salts through Diffusion,Overhauser, DFT and X‐ray Methods

Pulsed gradient spin‐echo (PGSE) diffusion characteristics for a) the new [brucinium][X] salts 6 a – f [ a : X=BF₄^?; b : X=PF₆^?; c : X=MeSO₃^?, d : X=CF₃SO₃^?; e : X=BArF^?; f : X=PtCl₃(C₂H₄)^?], b) 4‐tert‐butyl‐N‐benzyl analogue, 7 and c) the aryl carbocations (p‐R‐C₆H₄)₂CH 9 a (R=CH₃O) and 9 b (R=(CH₃)₂N), (p‐CH₃O‐C₆H₄)_xCPh_3?x⁺ 10 a – c (x=1–3, respectively) and (p‐R‐C₆H₄)₃C⁺ 11 (R=(CH₃)₂N) and 12 (R=H) all in several different solvents, are reported. The solvent dependence suggests strong ion pairing in CDCl₃, intermediate ion pairing in CD₂Cl₂ and little ion pairing in [D₆]acetone. ¹H, ¹⁹F HOESY NMR spectra (HOESY: heteronuclear Overhauser effect spectroscopy) for 6 and 7 reveal a specific approach of the anion with respect to the brucinium cation plus subtle changes, which are related to the anion itself. Further, for carbocations 9 – 12 , (all as BF₄^? salts) based on the NOE results, one finds marked changes in the relative positions of the BF₄^? anion. In these aryl cationic species the anion can be located either a) very close to the carbonium ion carbon b) in an intermediate position or c) proximate to the N or O atom of the p‐substituent and remote from the formally positive C atom. This represents the first example of such a positional dependence of an anion on the structure of the carbocation. DFT calculations support the experimental HOESY results. The solid‐state structures for 6 c and the novel Zeise's salt derivative, [brucinium][PtCl₃(C₂H₄)], 6 f , are reported. Analysis of ¹⁹⁵Pt NMR and other NMR measurements suggest that the η²‐C₂H₄ bonding to the platinum centre in 6 f is very similar to that found in K[PtCl₃(C₂H₄)]. Field dependent T₁ measurements on [brucinium][PtCl₃(C₂H₄)] and K[PtCl₃(C₂H₄)], are reported and suggested to be useful in recognizing aggregation effects.     

Tribenzotriquinacenes Based on Regioselective Bis‐formylation: Optical Resolution and Absolute Configuration of Inherently Chiral Derivatives and Synthesis of the First Cyclophane‐Type Tribenzotriquinacene Dimers

Enantiomerically pure tribenzotriquinacenes (TBTQs) bearing two monofunctionalized aromatic nuclei were synthesized for the first time and their optical properties and absolute configuration determined. A remarkably regioselective bis‐formylation of the fully bridgehead methylated parent TBTQ hydrocarbon with MeOCHCl₂/TiCl₄ afforded a mixture of two C_s‐symmetrical (achiral) difunctionalized derivatives together with one C₁‐symmetrical (chiral) isomer. Reduction and subsequent column chromatography furnished the three respective benzylic TBTQ dialcohols. Optical resolution of the racemic 2,6‐bis(hydroxymethyl) derivative was achieved via the diastereomeric (R)‐1,1′‐bi‐2‐naphthol ethers and the absolute configuration of the enantiomers was determined by CD exciton model analysis. The electronic circular dichroism (ECD) spectra and the specific rotation of the enantiomers were found to agree with the results of DFT calculations. Among the C_s‐symmetrical isomers, the “proximal” 2,11‐dialdehyde and the corresponding benzylic dialcohol were identified by 2D NMR spectroscopy and X‐ray crystallographic analysis, respectively, and used as the starting point for the synthesis of several novel dithiametacyclophanes. These include the first “dimeric” tribenzotriquinacene‐based cyclophanes bearing the bowls of the two TBTQ units attached to each other in a syn (concave–concave) or anti (convex–concave) configuration. The usefulness of such thiacyclophanes as fluorescent chemosensors for different metal ions is also demonstrated.     

Versatile Syntheses of Hemi‐Cryptophanes and a Metallo‐Cryptophane from a Hexa‐Functionalized C3v‐Symmetrical Tribenzotriquinacene (TBTQ) Derivative

A number of three‐fold C_3v‐symmetrical tribenzotriquinacene (TBTQ) cavitands were synthesized by a “metamorphosis‐to‐half” strategy, employing six‐fold etherification reactions between the hexakis(chloromethyl)‐TBTQ intermediate 2 a and various 5‐functionalized resorcinols. X‐ray structure analyses of single crystals of the cavitands revealed limited rotational flexibility of the resorcinol bridging units, which enables an apical, nearly co‐axial orientation of the three functional groups and, as a consequence, the construction of nanoscale cage‐like molecules via covalent or coordination bonding. On this basis, two TBTQ‐based hemicryptophanes were prepared from the TBTQ cavitands via covalent bond formation in good yields. A dumbbell‐shaped TBTQ‐based metallo‐cryptophane was also synthesized in 34 % yield by a solvothermal reaction between cadmium nitrate and two equivalents of the TBTQ‐cavitand triacid, as confirmed by single‐crystal X‐ray diffraction and MALDI‐ToF mass spectrometry.     

β,β‐(1,4‐Dithiino)subporphyrin Dimers Capturing Fullerenes with Large Association Constants

β,β‐(1,4‐Dithiino)subporphyrin dimers 7‐syn and 7‐anti were synthesized by the nucleophilic aromatic substitution reaction of 2‐bromo‐3‐(4‐methoxyphenylsulfonyl)subporphyrin 4 with 2,3‐dimercaptosubporphyrin 5 under basic conditions followed by axial arylation. Additions of C₆₀ or C₇₀ to a dilute solution of 7‐anti (ca. 10^?6 m ) in toluene did not cause appreciable UV/Vis spectral changes, while similar additions to a concentrated solution (ca. 10^?3 m ) resulted in precipitation of complexes. In contrast, dimer 7‐syn captured C₆₀ and C₇₀ in different complexation stoichiometries in toluene; a 1:1 manner and a 2:1 manner, respectively, with large association constants; K_a=(1.9±0.2)×10⁶ m ^?1 for C₆₀@ 7‐syn , and K₁=(1.6±0.5)×10⁶ and K₂=(1.8±0.9)×10⁵ m ^?1 for C₇₀@( 7‐syn )₂. These association constants are the largest for fullerenes‐capture by bowl‐shaped molecules reported so far. The structures of C₆₀@ 7‐anti , C₇₀@ 7‐anti , C₆₀@ 7‐syn , and C₇₀@ 7‐syn have been determined by single‐crystal X‐ray diffraction analysis.     

C3i‐Symmetric Octanuclear Cadmium Cages: Double‐Anion‐Templated Synthesis,Formation Mechanism,and Properties

A series of C_3i‐symmetric bicapped trigonal antiprismatic Cd₈ cages [2X@Cd₈L₆(H₂O)₆] ? n Y ? solvents (X=Cl^?, Y=NO₃^?, n=2: MOCC‐4 ; X=Br^?, Y=NO₃^?, n=2: MOCC‐5 ; X=NO₃^?, Y=NO₃^?, n=2: MOCC‐6 ; X=NO₃^?, Y=BF₄^?, n=2: MOCC‐7 ; X=NO₃^?, Y=ClO₄^?, n=2: MOCC‐8 ; X=CO₃^2?, n=0: MOCC‐9 ), doubly anion templated by different anions, were solvothermally synthesized by means of a flexible ligand. Interestingly, the CO₃^2? template for MOCC‐9 was generated in situ by two‐step decomposition of DMF solvent. For other MOCCs, spherical or trigonal monovalent anions could also play the role of template in their formation. The template abilities of these anions in the formation of the cages were experimentally studied and are discussed for the first time. Anion exchange of MOCC‐8 was carried out and showed anion‐size selectivity. All of the cage‐like compounds emit strong luminescence at room temperature.     

Synthesis,Interionic Structure,and Reactivity toward CO and p‐Methylstyrene of Palladacyclic Compounds Bearing α‐Diimine Ligands

Palladacyclic compounds [Pd(C₆H₄(C₆H₅C?O)C?N? R)(N? N)] [X] (R = Et, ⁱPr, 2,6‐ⁱPr₂C₆H₃; N? N = bpy = 2,2′‐bipyridine, or 1,4‐(o,o′‐dialkylaryl)‐1,4‐diazabuta‐1,3‐dienes; [X]^? = [BF₄]^? or [PF₆]^?) were synthesized from the dimers [{Pd(C₆H₄(C₆H₅C?O)C?N? R)(μ‐Cl)}₂] and N? N ligands. Their interionic structure in CD₂Cl₂ was determined by means of ¹⁹F,¹H‐HOESY experiments and compared with that in the solid state derived from X‐ray single‐crystal studies. [Pd(C₆H₄(C₆H₅C?O)C?N? R)(N? N)] [X] complexes were found to copolymerize CO and p‐methylstyrene affording syndiotactic or isotactic copolymers when bpy or 1,4‐(o,o′‐dimethylaryl)‐1,4‐diazabuta‐1,3‐dienes were used, respectively. The reactions with CO and p‐methylstyrene of the bpy derivatives were investigated. Two intermediates derived from a single and a double insertion of CO into the Pd? C bonds were isolated and completely characterized in solution.     

Towards a Molecular Understanding of Cation–Anion Interactions—Probing the Electronic Structure of Imidazolium Ionic Liquids by NMR Spectroscopy,X‐ray Photoelectron Spectroscopy and Theoretical Calculations

Ten [C₈C₁Im]⁺ (1‐methyl‐3‐octylimidazolium)‐based ionic liquids with anions Cl^?, Br^?, I^?, [NO₃]^?, [BF₄]^?, [TfO]^?, [PF₆]^?, [Tf₂N]^?, [Pf₂N]^?, and [FAP]^? (TfO=trifluoromethylsulfonate, Tf₂N=bis(trifluoromethylsulfonyl)imide, Pf₂N=bis(pentafluoroethylsulfonyl)imide, FAP=tris(pentafluoroethyl)trifluorophosphate) and two [C₈C₁C₁Im]⁺ (1,2‐dimethyl‐3‐octylimidazolium)‐based ionic liquids with anions Br^? and [Tf₂N]^? were investigated by using X‐ray photoelectron spectroscopy (XPS), NMR spectroscopy and theoretical calculations. While ¹H NMR spectroscopy is found to probe very specifically the strongest hydrogen‐bond interaction between the hydrogen attached to the C² position and the anion, a comparative XPS study provides first direct experimental evidence for cation–anion charge‐transfer phenomena in ionic liquids as a function of the ionic liquid’s anion. These charge‐transfer effects are found to be surprisingly similar for [C₈C₁Im]⁺ and [C₈C₁C₁Im]⁺ salts of the same anion, which in combination with theoretical calculations leads to the conclusion that hydrogen bonding and charge transfer occur independently from each other, but are both more pronounced for small and more strongly coordinating anions, and are greatly reduced in the case of large and weakly coordinating anions.     

pH‐Controlled Molecular Switches and the Substrate‐Directed Self‐Assembly of Molecular Capsules with a Calix[4]pyrrole Derivative

10α,20α‐Bis(4‐nitrophenyl)calix[4]pyrrole ( 1 ) forms 1:1 complexes with anions of selected aromatic hydroxy acids in which the host orientation within the guest is controlled by a change in the pH value. Some bis‐anionic guests, including those obtained from 4‐hydroxybenzoic acid, 1,4‐ and 1,3‐benzenedicarboxylic acids, induce the self‐assembly of molecular capsules involving two molecules of the receptor. ¹H NMR data and solid‐state structures of the 1:1 complex of 1 with p‐C₆H₄(COOH)(COO^?)⁺NMe₄ and the 2:1 capsule [( 1 )₂m‐C₆H₄(COO^?)₂(⁺NMe₄)₂] provide structural details in solution and in the solid state.     

Synthesis,Structure, and Properties of the Fullerene C60 Salt of Crystal Violet, (CV+)(C60.−)⋅0.5 C6H4Cl2, which Contained Closely Packed Zigzagged C60.− Chains

The reduction of fullerene C₆₀ by zinc dust in the presence of crystal violet cations (CV⁺) yielded a deep‐blue solution, from which crystals of (CV⁺)(C₆₀^.?) ? 0.5 C₆H₄Cl₂ ( 1 ) were obtained by slow mixing with n‐hexane. The salt contained isolated, closely packed zigzagged chains that were composed of C₆₀^.? radical anions with a uniform interfullerene center‐to‐center distance of 9.98 Å. In spite of the close proximity of the fullerenes, they did not dimerize, owing to spatial separation by the phenyl substituents of CV⁺. The room‐temperature conductivity of compound 1 was 3×10^?2 S cm^?1 along the fullerene chains. The salt exhibited semiconducting behavior, with an activation energy of E_a=167 meV. Spins localized on C₆₀^.? were antiferromagnetically coupled within the fullerene chains, with a Weiss temperature of ?19 K without long‐range magnetic ordering down to 1.9 K.     

Exploring the structural landscape of 2‐(thiophen‐2‐yl)‐1,3‐benzothiazole: high‐Z′ packing polymorphism and cocrystallization with calix[4]tube

We report here for the first time a cocrystal of the so‐called neutral calix[4]tube, which is two tail‐to‐tail‐arranged and partially deprotonated tetrakis(carboxymethoxy)calix[4]arenes, including three sodium ions, with 2‐(thiophen‐2‐yl)‐1,3‐benzothiazole, namely trisodium bis(carboxymethoxy)bis(carboxylatomethoxy)calix[4]arene tris(carboxymethoxy)(carboxylatomethoxy)calix[4]arene–2‐(thiophen‐2‐yl)‐1,3‐benzothiazole–dimethyl sulfoxide–water (1/1/2/2), 3Na⁺·C₃₆H₃₀O₁₂^2?·C₃₆H₃₁O₁₂^?·C₁₁H₇NS₂·2C₂H₆OS·2H₂O, which provides a new approach into the host–guest chemistry of inclusion complexes. Three packing polymorphs of the same benzothiazole with high Z′ (one with Z′ = 8 and two with Z′ = 4) were also discovered in the course of our desired cocrystallization. The inspection of these polymorphs and a previously known polymorph with Z′ = 2 revealed that Z′ increases as the strength of intermolecular contacts decreases. Also, these results expand the frontier of invoking calixarenes as a host for nonsolvent small molecules, besides providing knowledge on the rare formation of high‐Z′ packing polymorphs of simple molecules, such as the target benzothiazole.     

2(S)‐Amino‐3‐[1H‐imidazol‐4(5)‐yl]­propyl cyclo­hexylmethyl ether di­hydro­chloride and 2(S)‐amino‐3‐[1H‐imidazol‐4(5)‐yl]­propyl 4‐bromo­benzyl ether di­hydro­chloride

(Cyclo­hexyl­methyl­oxy­methyl)(1H‐imidazol‐4‐io­methyl)‐(S)‐ammonium dichloride, C₁₃H₂₅N₃O⁺·2Cl^?, and (4‐bromo­benzyl)(1H‐imidazol‐4‐io­methyl)‐(S)‐ammonium dichloride, C₁₃H₁₈BrN₃O⁺·2Cl^?, are model compounds with different biological activities for evaluation of the hist­amine H3‐receptor activation mechanism. Both title compounds occur in almost similar extended conformations.     

Cationic Allyl Complexes of the Rare‐Earth Metals: Synthesis,Structural Characterization,and 1,3‐Butadiene Polymerization Catalysis

Monocationic bis‐allyl complexes [Ln(η³‐C₃H₅)₂(thf)₃]⁺[B(C₆X₅)₄]^? (Ln=Y, La, Nd; X=H, F) and dicationic mono‐allyl complexes of yttrium and the early lanthanides [Ln(η³‐C₃H₅)(thf)₆]²⁺[BPh₄]₂^? (Ln=La, Nd) were prepared by protonolysis of the tris‐allyl complexes [Ln(η³‐C₃H₅)₃(diox)] (Ln=Y, La, Ce, Pr, Nd, Sm; diox=1,4‐dioxane) isolated as a 1,4‐dioxane‐bridged dimer (Ln=Ce) or THF adducts [Ln(η³‐C₃H₅)₃(thf)₂] (Ln=Ce, Pr). Allyl abstraction from the neutral tris‐allyl complex by a Lewis acid, ER₃ (Al(CH₂SiMe₃)₃, BPh₃) gave the ion pair [Ln(η³‐C₃H₅)₂(thf)₃]⁺[ER₃(η¹‐CH₂CH?CH₂)]^? (Ln=Y, La; ER₃=Al(CH₂SiMe₃)₃, BPh₃). Benzophenone inserts into the La? C_allyl bond of [La(η³‐C₃H₅)₂(thf)₃]⁺[BPh₄]^? to form the alkoxy complex [La{OCPh₂(CH₂CH?CH₂)}₂(thf)₃]⁺[BPh₄]^?. The monocationic half‐sandwich complexes [Ln(η⁵‐C₅Me₄SiMe₃)(η³‐C₃H₅)(thf)₂]⁺[B(C₆X₅)₄]^? (Ln=Y, La; X=H, F) were synthesized from the neutral precursors [Ln(η⁵‐C₅Me₄SiMe₃)(η³‐C₃H₅)₂(thf)] by protonolysis. For 1,3‐butadiene polymerization catalysis, the yttrium‐based systems were more active than the corresponding lanthanum or neodymium homologues, giving polybutadiene with approximately 90 % 1,4‐cis stereoselectivity.     

Unique Stereocontrol in Carborane Chemistry: Skeletal Alkylcarbonation (SAC) versus Exoskeletal Alkylmethylation (EAM) Reactions

Reactions between the arachno‐6,9‐C₂B₈H₁₄ ( 1 ) dicarbaborane and acyl chlorides, RCOCl ( 2 ), are subject to stereocontrol that completely changes the nature of the reaction products. While most chlorides produce the 8‐R‐nido‐7,8,9‐C₃B₈H₁₁ ( 3 ) tricarbollides (by skeletal alkylcarbonation=SAC), bulky RCOCls ( 2 ; where R=1‐adamantyl, 2 a ; 1‐mesityl, 2 b ; 9‐anthranyl, 2 c ; 1‐naphthyl, 2 d ) in 1,2‐dichloroethane (DCE) in the presence of triethylamine at 40–60 °C gave a series of entirely different 1‐R‐2‐CH₃‐closo‐1,6‐C₂B₈H₈ ( 4 ) dicarbaboranes upon acidification with conc. H₂SO₄ (by exosleletal alkylmehylation=EAM). Both types of reactions seem to proceed via a common [8‐R‐nido‐7,8,9‐C₃B₈H₁₀]^? ( 3^? ) anion which in the EAM case is unstable because of steric crowd and undergoes rearrangement via the isomeric [R‐nido‐7,8,10‐C₃B₈H₁₀]^? tricarbollide structures which, on protonation, undergo reductive extraction of one CH vertex to generate the 2‐CH₃ substituent in structure 4 .     

Dispersion of Reduced Graphene Oxide in Multiple Solvents with an Imidazolium‐Modified Hexa‐peri‐hexabenzocoronene

An imidazolium‐modified hexa‐peri‐hexabenzocoronene derivative (HBC‐C₁₁‐MIM[Cl^?]) was designed and synthesized as a stabilizer to fabricate reduced graphene oxide (RGO). The resulting RGO/HBC‐C₁₁‐MIM[Cl^?] hybrid shows excellent dispersivity (5.0 mg mL^?1) and stability in water. RGO/HBC‐C₁₁‐MIM[Cl^?] was comprehensively characterized by using atomic force microscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy, thermogravimetric analysis, and Raman spectroscopy, thus revealing that one HBC‐C₁₁‐MIM[Cl^?] group can stabilize about 178 carbon atoms on the graphene sheets. The obtained hybrid film exhibits a high conductivity of 286 S m^?1. Furthermore, the HBC‐C₁₁‐MIM[Cl^?]‐modified RGO sheets can be readily dispersed in polar organic solvents upon exchange of the hydrophilic Cl^? ions for hydrophobic bis(trifluoromethylsulfonyl) amide (NTf₂^?) ions.     

Synthesis,characterization and theoretical and fluorescence emission microscopy studies of new Pd/Pt–cyclopropa[60]fullerene complexes: Application of Taguchi method for optimization of parameters in Suzuki–Miyaura reaction

The reactions of unsymmetric phosphorus ylides of the type [Ph₂P(CH₂)_nPPh₂?C(H)C(O)C₆H₄‐p‐CN] (n = 1 (Y¹); n = 2 (Y²)) with C₆₀ and M(dba)₂ (M = Pd or Pt; dba = dibenzylideneacetone) are reported. Based on the various coordination modes of these ylides in complexation, the following new Pd/Pt–cyclopropa[60]fullerene complexes were obtained: P,C‐coordinated [(η²‐C₆₀)Pd(κ²‐Y¹)] ( 1 ) and [(η²‐C₆₀)Pt(κ²‐Y¹)] ( 2 ) complexes and P‐coordinated [(η²‐C₆₀)Pd(Y²)₂] ( 3 ) and [(η²‐C₆₀)Pt(Y²)₂] ( 4 ) complexes. These compounds were characterized using Fourier transform infrared, UV–visible and NMR (¹H, ¹³C and ³¹P) spectroscopies and scanning electron microscopy. Furthermore, cytotoxicity studies showed that nanoparticles of these complexes can be used as non‐toxic labels for cellular imaging application. Also energy decomposition analysis results revealed that the percentage contribution of ΔE_elec in total interaction energy is considerably larger than that of ΔE_orb. Thus, in all complexes the (η²‐C₆₀)M? (Y¹) bond is considerably more electrostatic in nature than the (η²‐C₆₀)? M(Y¹) bond. Finally, by application of the Taguchi method for optimization of parameters in Suzuki–Miyaura reaction, the catalytic activity of Pd complexes 1 and 3 was investigated in the cross‐coupling reaction of various aryl chlorides with phenylboronic acid. According to analysis of variance results, solvent has the highest F value and it has high contribution percentage (36.75%) to the yield of Suzuki–Miyaura reaction.