RhI‐Catalyzed Bimolecular Cyclization between Two Different 1,5‐Bisallenes: A Combinatorial One‐Step Approach to Heterosteroids and Mechanistic Implications

In this paper, a bimolecular‐cyclization reaction between two different bis(allene)s with at least one heteroatom as the tether under the catalysis of trans‐[RhCl(CO)(PPh₃)₂] is described. This protocol provides an efficient entry to different heterocyclic 18,19‐norsteroid‐like scaffolds. The tricyclic product was formed highly selectively from the cyclization reaction of bis(2,3‐butadienyl)sulfide with dimethyl 2‐bis(2′,3′‐butadienyl)malonate, which sheds light on the mechanism involving the metalla‐[4.3.0]‐bicyclic intermediate formed by the cyclometallation of the terminal and the internal C=C bonds of each of the two allene moieties in 2‐bis(2′,3′‐butadienyl)malonate.     

Optically Active Macrocyclic cis‐3 Bis‐Adducts of C60: Regio‐ and Stereoselective Synthesis,Exciton Chirality Coupling,and Determination of the Absolute Configuration,and First Observation of Exciton Coupling between Fullerene Chromophores in a Chiral Environment

A series of optically active cis‐3 bis‐adducts, such as (R,R,^fC)‐ 16 (Scheme 6), was obtained regio‐ and diastereoselectively by Bingel macrocyclization of C₆₀ with bis‐malonates, which contain optically active tethers derived from 1,2‐diols. The absolute configuration of the inherently chiral addition pattern in cis‐3 bis‐adducts had previously been determined by comparison of calculated and experimental circular dichroism (CD) spectra. Full confirmation of these earlier assignments was now obtained by an independent method based on semiempirical AM1 (`Austin Model 1') and OM2 (`Orthogonalization Method 2') calculations combined with ¹H‐NMR spectroscopy. It was found computationally that bis‐malonates [CHR(OCOCH₂COOEt)]₂, which contain (R,R)‐ or (S,S)‐butane‐2,3‐diol derivatives as optically active tethers, preferentially form out‐out cis‐3 bis‐adducts of C₆₀ as a single diastereoisomer in which the alkyl groups R adopt a gauche conformation, while the two glycolic H‐atoms are in an antiperiplanar (ap) and the ester linkages to the fullerene in a gauche relationship (Figs. 2 and 5). In contrast, in the less favorable diastereoisomer, which should not form, the alkyl groups R adopt an ap and the H‐atoms a gauche conformation, while the ester bridges to the fullerene remain, for geometric reasons, locked in a gauche conformation. According to the OM2 calculations, the geometry of the fully staggered tether in the free bis‐malonates closely resembles the conformation of the tether fragment in the bis‐adducts formed. These computational predictions were confirmed experimentally by the measurement of the coupling constant between the vicinal glycolic H‐atoms in the ¹H‐NMR spectrum. For (R,R,^fC)‐ 16 , ³J(H,H) was determined as 7.9 Hz, in agreement with the ap conformation, and, in combination with the calculations, this allowed assignment of the ^fC‐configuration to the inherently chiral addition pattern. This conformational analysis was further supported by the regio‐ and diastereoselective synthesis of cis‐3 bis‐adducts from bis‐malonates, including tethers derived from cyclic glycol units with a fixed gauche conformation of the alkyl residues R at the glycolic C‐atoms. Thus, a bis‐malonate of (R,R)‐cyclohexane‐1,2‐diol provided exclusively cis‐3 bis‐adduct (R,R,^fC)‐ 20 in 32% yield (Scheme 7). Incorporation of a tether derived from methyl 4,6‐O,O‐benzylidene‐α‐D ‐glucopyranoside into the bis‐malonate and Bingel macrocyclization diastereoselectively produced the cis‐3 stereoisomer (α,D ,^fA)‐ 22 (Scheme 8) as the only macrocyclic bis‐adduct. If the geometry of the alkyl groups R at the glycolic C‐atoms of the tether component deviates from a gauche relationship, as in the case of tethers derived from exo cis‐ and trans‐norbornane‐2,3‐diol or from trans‐cyclopentane‐1,2‐diol, hardly any macrocyclic product is formed (Schemes 5 and 9). The absolute configurations of the various optically active cis‐3 bis‐adducts were also assigned by comparison of their CD spectra, which are dominated by the chiroptical contributions of the inherently chiral fullerene chromophore (Figs. 1, 3, and 4). A strong chiral exciton coupling was observed for optically active macrocyclic cis‐3 bis‐adducts of C₆₀ with two appended 4‐(dimethylamino)benzoate ((S,S,^fC)‐ 26 ; Fig. 6) or meso‐tetraphenylporphyrin ((R,R,^fC)‐ 28 ; Fig. 7) chromophores. Chiral exciton coupling between two fullerene chromophores was observed for the first time in the CD spectrum of the threitol‐bridged bis‐fullerene (R,R)‐ 35 (Fig. 9).     

Synthesis of Amphiphilic Fullerene Derivatives and Their Incorporation in Langmuir and Langmuir‐Blodgett Films

Various amphiphilic fullerene derivatives were prepared by functionalization of [5,6]fullerene‐C₆₀‐I_h (C₆₀) with malonate or bis‐malonate derivatives obtained by esterification of the malonic acid mono‐esters 5 – 7 . Cyclopropafullerene 10 was obtained by protection of the carboxylic acid function of 6 as a tert‐butyl ester, followed by Bingel addition to C₆₀ and a deprotection step (Scheme 2). The preparation of 10 was also attempted directly from the malonic acid mono‐ester 6 under Bingel conditions. Surprisingly, the corresponding 3′‐iodo‐3′H‐cyclopropa[1,9][5,6]fullerene‐C₆₀‐I_h‐3′‐carboxylate 11 was formed instead of 10 (Scheme 3). The general character of this new reaction was confirmed by the preparation of 15 and 16 from the malonic acid mono‐esters 13 and 14 , respectively (Scheme 4). All the other amphiphilic fullerene derivatives were prepared by taking advantage of the versatile regioselective reaction developed by Diederich and co‐workers which led to macrocyclic bis‐adducts of C₆₀ by a cyclization reaction at the C‐sphere with bis‐malonate derivatives in a double Bingel cyclopropanation. The bis‐adducts 37 – 39 with a carboxylic acid polar head group and four pendant long alkyl chains of different length were prepared from diol 22 and acids 5 – 7 , respectively (Scheme 9). In addition, the amphiphilic fullerene derivatives 45, 46, 49, 54 , and 55 bearing different polar head groups and compound 19 with no polar head group were synthesized (Schemes 11–13, 15, and 5, resp.). The ability of all these compounds to form Langmuir monolayers at the air‐water interface was investigated in a systematic study. The films at the water surface were characterized by their surface pressure vs. molecular area isotherms, compression and expansion cycles, and Brewster‐angle microscopy. The spreading behavior of compound 10 was not good, the two long alkyl chains in 10 being insufficient to prevent aggregation resulting from the strong fullerene‐fullerene interactions. While no films could be obtained from compound 19 with no polar head group, all the corresponding amphiphilic fullerene bis‐adducts showed good spreading characteristics and reversible behavior upon successive compression/expansion cycles. The encapsulation of the fullerene in a cyclic addend surrounded by four long alkyl chains is, therefore, an efficient strategy to prevent the irreversible aggregation resulting from strong fullerene‐fullerene interactions usually observed for amphiphilic C₆₀ derivatives at the air‐water interface. The balance of hydrophobicity to hydrophilicity was modulated by changing the length of the surrounding alkyl chains or the nature of the polar head group. The best results in terms of film formation and stability were obtained with the compounds having the largest polar head group, i.e. 45 and 46 , and dodecyl chains. Finally, the Langmuir films obtained from the amphiphilic fullerene bis‐adducts were transferred onto solid substrates, yielding high‐quality Langmuir‐Blodgett films.     

Regioselective One‐Step Synthesis and Topological Chirality of trans‐3, trans‐3,trans‐3 and e,e,e [60]Fullerene‐Cyclotriveratrylene Tris‐adducts: Discussion on a Topological meso‐Form

The C₃‐symmetrical [60]fullerene‐cyclotriveratrylene (CTV) tris‐adducts (±)‐ 1 (with a trans‐3,trans‐3,trans‐3 addition pattern) and (±)‐ 2 (with an e,e,e addition pattern) were prepared in 11 and 9% yield, respectively, by the regio‐ and diastereoselective tether‐directed Bingel reaction of C₆₀ with the tris‐malonate‐appended CTV derivative (±)‐ 3 (Scheme). This is the first example for tris‐adduct formation by a one‐step tether‐directed Bingel addition. Interchromophoric interactions between the electron‐rich CTV cap and the electron‐attracting fullerene moiety have a profound effect on the electrochemical behavior of the C‐sphere (Fig. 4 and Table 1). The fullerene‐centered first reduction potentials in compounds (±)‐ 1 and (±)‐ 2 are by 100 mV more negative than those of their corresponding tris[bis(ethoxycarbonyl)methano][60]fullerene analogs that lack the CTV cap. A particular interest in (±)‐ 1 and (±)‐ 2 arises from the topological chirality of these molecules. A complete topology study is presented, leading to the conclusion that the four possible classical stereoisomers of the e,e,e regioisomer are topologically different, and, therefore, there exist four different topological stereoisomers (Fig. 6). Interestingly, in the case of the trans‐3,trans‐3,trans‐3 tris‐adduct, there are four classical stereoisomers but only two topological stereoisomers (Fig. 7). An example of a target molecule representing a topological meso‐form is also presented (Fig. 8).     

Hexakis‐Adducts of [60]Fullerene with Different Addition Patterns: Templated Synthesis,Physical Properties,and Chemical Reactivity

Representatives of two classes of hexakis‐adducts of C₆₀ were prepared by templated synthesis strategies. Compound 8 with a dipyridylmethano addend in a pseudo‐octahedral addition pattern was obtained by DMA‐templated addition (DMA=9,10‐dimethylanthracene; Scheme 1) and served as the starting material for the first supramolecular fullerene dimer 2 . Hexakis‐adduct 12 also possesses a pseudo‐octahedral addition pattern and was obtained by a sequence of tether‐directed remote functionalization, tether removal, and regioselective bis‐functionalization (Scheme 2). With its two diethynylmethano addends in trans‐1 position, it is a precursor for fascinating new oligomers and polymers that feature C₆₀ moieties as part of the polymeric backbone (Fig. 1). With the residual fullerene π‐electron chromophore reduced to a `cubic cyclophane'‐type sub‐structure (Fig. 4), and for steric reasons, 8 and 12 no longer display electrophilic reactivity. As a representative of the second class of hexakis‐adducts, (±)‐ 1 , which features six addends in a distinct helical array along an equatorial belt, was prepared by a route that involved two sequential tether‐directed remote functionalization steps (Schemes 3 and 5). In compound (±)‐ 1 , π‐electron conjugation between the two unsubstituted poles of the carbon sphere is maintained via two (E)‐stilbene‐like bridges (Fig. 4). As a result, (±)‐ 1 features very different chemical reactivity and physical properties when compared to hexakis‐adducts with a pseudo‐octahedral addition pattern. Its reduction under cyclic voltammetric conditions is greatly facilitated (by 570 mV), and it readily undergoes additional, electronically favored Bingel additions at the two sterically well‐accessible central polar 6‐6 bonds under formation of heptakis‐ and octakis‐adducts, (±)‐ 30 and (±)‐ 31 , respectively (Scheme 6). The different extent of the residual π‐electron delocalization in the fullerene sphere is also reflected in the optical properties of the two types of hexakis‐adducts. Whereas 8 and 12 are bright‐yellow (end‐absorption around 450 nm), compound (±)‐ 1 is shiny‐red, with an end‐absorption around 600 nm. This study once more demonstrates the power of templated functionalization strategies in fullerene chemistry, providing addition patterns that are not accessible by stepwise synthetic approaches.     

Supramolecular Fullerene Chemistry: A Comprehensive Study of Cyclophane‐Type Mono‐ and Bis‐Crown Ether Conjugates of C70

The covalently templated bis‐functionalization of C₇₀, employing bis‐malonate 5 tethered by an anti‐disubstituted dibenzo[18]crown‐6 (DB18C6) ether, proceeds with complete regiospecificity and provides two diastereoisomeric pairs of enantiomeric C₇₀ crown ether conjugates, (±)‐ 7a and (±)‐ 7b , featuring a five o'clock bis‐addition pattern that is disfavored in sequential transformations (Scheme 1). The identity of (±)‐ 7a was revealed by X‐ray crystal‐structure analysis (Fig. 6). With bis‐malonate 6 containing a syn‐disubstituted DB18C6 tether, the regioselectivity of the macrocylization via double Bingel cyclopropanation changed completely, affording two constitutionally isomeric C₇₀ crown ether conjugates in a ca. 1 : 1 ratio featuring the twelve ( 16 ) and two o'clock ((±)‐ 15 ) addition patterns, respectively (Scheme 3). The X‐ray crystal‐structure analysis of the twelve o'clock bis‐adduct 16 revealed that a H₂O molecule was included in the crown ether cavity (Figs. 7 and 8). Two sequential Bingel macrocyclizations, first with anti‐DB18C6‐tethered ( 5 ) and subsequently with syn‐DB18C6‐tethered ( 6 ) bis‐malonates, provided access to the first fullerene bis‐crown ether conjugates. The two diastereoisomeric pairs of enantiomers (±)‐ 28a and (±)‐ 28b were formed in high yield and with complete regioselectivity (Scheme 9). The cation‐binding properties of all C₇₀ crown‐ether conjugates were determined with the help of ion‐selective electrodes (ISEs). Mono‐crown ether conjugates form stable 1 : 1 complexes with alkali‐metal ions, whereas the tetrakis‐adducts of C₇₀, featuring two covalently attached crown ethers, form stable 1 : 1 and 1 : 2 host‐guest complexes (Table 2). Comparative studies showed that the conformation of the DB18C6 ionophore imposed by the macrocyclic bridging to the fullerene is not particularly favorable for strong association. Reference compound (±)‐ 22 (Scheme 4), in which the DB18C6 moiety is attached to the C₇₀ sphere by a single bridge only and, therefore, possesses higher conformational flexibility, binds K⁺ and Na⁺ ions better by factors of 2 and 20, respectively. Electrochemical studies demonstrate that cation complexation at the crown ether site causes significant anodic shifts of the first reduction potential of the appended fullerene (Table 3). In case of the C₇₀ mono‐crown ether conjugates featuring a five o'clock functionalization pattern, addition of 1 equiv. of KPF₆ caused an anodic shift of the first reduction wave in the cyclic voltammogram (CV) by 70 to 80 mV, which is the result of the electrostatic effect of the K⁺ ion bound closely to the fullerene core (Fig. 14). Addition of 2 equiv. of K⁺ ions to C₇₀ bis‐crown ether conjugates resulted in the observation of only one redox couple, whose potential is anodically shifted by 170 mV with respect to the corresponding wave in the absence of the salt (Fig. 16). The synthesis and characterization of novel tris‐ and tetrakis‐adducts of C₇₀ are reported (Schemes 5 and 6). Attempts to prepare even more highly functionalized derivatives resulted in the formation of novel pentakis‐ and hexakis‐adducts and a single heptakis‐adduct (Scheme 7), which were characterized by ¹H‐ and ¹³C‐NMR spectroscopy (Fig. 10), as well as matrix‐assisted laser‐desorption‐ionization mass spectrometry (MALDI‐TOF‐MS). Based on predictions from density‐functional‐theory (DFT) calculations (Figs. 12 and 13), structures are proposed for the tris‐, tetrakis‐, and pentakis‐adducts.     

Layer‐by‐Layer Assemblies of Catechol‐Functionalized TiO2 Nanoparticles and Porphyrins through Electrostatic Interactions

In the current work, we present the successful functionalization and stabilization of P‐25 TiO₂ nanoparticles by means of N1,N7‐bis(3‐(4‐tert‐butyl‐pyridium‐methyl)phenyl)‐4‐(3‐(3‐(4‐tert‐butyl‐pyridinium‐methyl)phenylamino)‐3‐oxopropyl)‐4‐(3,4‐dihydroxybenzamido)heptanediamide tribromide ( 1 ). The design of the latter is aimed at nanoparticle functionalization and stabilization with organic building blocks. On one hand, 1 features a catechol anchor to enable its covalent grafting onto the TiO₂ surface, and on the other hand, positively charged pyridine groups at its periphery to prevent TiO₂ agglomeration through electrostatic repulsion. The success of functionalization and stabilization was corroborated by thermogravimetric analysis, dynamic light‐scattering, and zeta potential measurements. As a complement to this, the formation of layer‐by‐layer assemblies, which are governed by electrostatic interactions, by alternate deposition of functionalized TiO₂ nanoparticles and two negatively charged porphyrin derivatives, that is, 5,10,15,20‐(phenoxyacetic acid)‐porphyrin ( 2 ) and 5,10,15,20‐(4‐(2‐ethoxycarbonyl)‐4‐(2‐phenoxyacetamido)heptanedioic acid)‐porphyrin ( 3 ), is documented. To this end, the layer‐by‐layer deposition is monitored by UV/Vis spectroscopy, scanning electron microscopy, ellipsometry, and profilometry techniques. The resulting assemblies are utilized for the construction and testing of novel solar cells. From stable and repeatable photocurrents generated during several “on‐off” cycles of illumination, we derive monochromatic incident photo‐to‐current conversion efficiencies of around 3 %.     

Amphiphilic silicones prepared from branched PEO‐silanes with siloxane tethers

Amphiphilic silicones were prepared by the covalent incorporation of branched polyethylene oxide (PEO) via a siloxane tether. This was achieved by using six novel branched PEO‐silanes with varying siloxane tether lengths and PEO molecular weight (M_n). Each PEO‐silane was crosslinked via acid‐catalyzed sol–gel condensation with α,ω‐bis(Si‐OH)polydimethylsiloxane (PDMS) (M_n = 3000 g/mol) to yield six amphiphilic silicone films. Film surface hydrophilicity increased with siloxane tether length, particularly after exposure to an aqueous environment, indicating that the PEO segments were more readily driven to the surface. This effect was more pronounced for films prepared with PEO‐silanes containing lower M_n PEO segments. AFM was used to study surface reconstruction of films upon exposure to an aqueous environment. Adsorption of bovine serum albumin (BSA) and human fibrinogen (HF) proteins decreased with siloxane tether length, particularly after first exposing films to an aqueous environment. For a given siloxane tether length, relatively less BSA adsorbed onto films prepared with PEO‐silanes with lower M_n PEO segments whereas less HF adsorbed onto films prepared with PEO‐silanes with higher M_n PEO segments. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4108–4119, 2010     

Hydrogen phosphate and dihydrogen phosphate salts of 4‐amino­azobenzene

4‐Amino‐trans‐azobenzene {or 4‐[(E)‐phenyl­diazen­yl]aniline} can form isomeric salts depending on the site of protonation. Both orange bis{4‐[(E)‐phenyl­diazen­yl]anilinium} hydrogen phos­phate, 2C₁₂H₁₂N₃⁺·HPO₄²⁻, and purple 4‐[(E)‐phenyl­diazen­yl]­anilinium dihydrogen phosphate phosphoric acid solvate, C₁₂H₁₂N₃⁺·H₂PO₄⁻·H₃PO₄, (II), have layered structures formed through O—H⋯O and N—H⋯O hydrogen bonds. Additionally, azobenzene fragments in (I) are assembled through C—H⋯π inter­actions and in (II) through π–π inter­actions. Arguments for the colour difference are tentatively proposed.     

5′‐Allyl‐2′‐benzoyloxy‐3′‐methoxy‐4‐nitroazobenzene

The structure of the title compound, 4‐allyl‐2‐methoxy‐6‐[(4‐nitrophenyl)diazenyl]phenyl benzoate, C₂₃H₁₉N₃O₅, displays the characteristic features of azobenzene derivatives. The azobenzene moiety of the molecule has a trans configuration and in this moiety, average C—N and N=N bond lengths are 1.441 (3) and 1.241 (3) Å, respectively.     

Supported Membranes with Well‐Defined Polymer Tethers—Incorporation of Cell Receptors

We report the design of supported lipid membranes attached to the surface by tailored lipopolymer tethers. A series of well‐defined lipopolymers were synthesized by means of living cationic polymerization of 2‐methyl‐2‐oxazolines. The polymers were equipped with a silane coupling group on the proximal, and lipid anchors on the distal chain ends. The length of the intermediate hydrophilic polymer tether was varied (n=14, 18, 33) to change the distance between the membrane and the substrate. Supported membranes have been prepared in two‐steps. First, a suitable lipopolymer/lipid mixture was deposited by Langmuir–Blodgett transfer, and annealed to establish the covalent coupling to the surface. On the dry lipopolymer/lipid monolayer, the upper leaflet was deposited by vesicle fusion. Optimization of both preparation steps resulted in the formation of stable and defect‐free membranes. Impacts of the spacer length and the lipopolymer fraction upon the lateral diffusivity of the lipids were systematically compared by fluorescence recovery after photobleaching (FRAP). First experiments on the incorporation of a large transmembrane cell receptor (integrin α_IIbβ₃) into the polymer‐tethered membrane suggested that the length of the polymer tether plays a crucial role in distribution of the proteins on the surface.     

Synthesis of original benzo[g]quinoxaline‐5,10‐diones by bis‐SRN1 methodology

A new heterocyclic bioreductive bis‐alkylating agent, 2,3‐bis(chloromethyl)benzo[g]quinoxaline‐5,10‐dione, was prepared in a four‐steps synthesis. It was shown to react under electron transfer conditions with 2‐nitropropane anion by an bis‐S_RN1 mechanism to give three C‐alkylation products in excellent yields. Extension of this bis‐S_RN1 reaction to various nitronate or malonate anions and S‐centered anions led to a new class of potentially active benzo[g]quinoxaline‐5,10‐dione derivatives.     

Photoinduced Reversible Solid‐to‐Liquid Transitions for Photoswitchable Materials

Heating and cooling can induce reversible solid‐to‐liquid transitions of matter. In contrast, athermal photochemical processes can induce reversible solid‐to‐liquid transitions of some newly developed azobenzene compounds. Azobenzene is photoswitchable. UV light induces trans‐to‐cis isomerization; visible light or heat induces cis‐to‐trans isomerization. Trans and cis isomers usually have different melting points (T_m) or glass transition temperatures (T_g). If T_m or T_g of an azobenzene compound in trans and cis forms are above and below room temperature, respectively, light may induce reversible solid‐to‐liquid transitions. In this Review, we introduce azobenzene compounds that exhibit photoinduced reversible solid‐to‐liquid transitions, discuss the mechanisms and design principles, and show their potential applications in healable coatings, adhesives, transfer printing, lithography, actuators, fuels, and gas separation. Finally, we discuss remaining challenges in this field.     

Host–Guest Chemistry of a Bis‐Calix[4]pyrrole Derivative Containing a trans/cis‐Switchable Azobenzene Unit with Several Aliphatic Bis‐Carboxylates

The azobenzene unit used as a photochemically and thermally switchable linker in the assembly of a bis‐calix[4]pyrrole receptor provides a means to modulate the binding of bis‐carboxylates of significant biological importance in cancer research. Conversely, the complexation of different bis‐anionic guests has significant kinetic effects on both the photochemical and thermal trans/cis isomerization of the azobenzene unit.     

Water‐soluble triply‐responsive homopolymers of N,N‐dimethylaminoethyl methacrylate with a terminal azobenzene moiety

Novel water‐soluble triply‐responsive homopolymers of N,N‐dimethylaminoethyl methacrylate (DMAEMA) containing an azobenzene moiety as the terminal group were synthesized by atom transfer radical polymerization (ATRP) technique. The ATRP process of DMAEMA was initiated by an azobenzene derivative substituted with a 2‐bromoisobutyryl group (Azo‐Br) in the presence of CuCl/Me₆TREN in 1,4‐dioxane as a catalyst system. The molecular weights and their polydispersities of the resulting homopolymers (Azo‐PDMAEMA) were characterized by gel permeation chromatography (GPC). The homopolymers are soluble in aqueous solution and exhibit a lower critical solution temperature (LCST) that alternated reversibly in response to Ph and photoisomerization of the terminal azobenzene moiety. It was found that the LCST increased as pH decreased in the range of testing. Under UV light irradiation, the trans‐to‐cis photoisomerization of the azobenzene moiety resulted in a higher LCST, whereas it recovered under visible light irradiation. This kind of polymers should be particularly interesting for a variety of potential applications in some promising areas, such as drug controlled‐releasing carriers and intelligent materials because of the multistimuli responsive property. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2564–2570, 2010     

Hydrogen‐bonded chains in 2,2,2‐trichloro‐N,N′‐bis(4‐methoxyphenyl)ethane‐1,1‐diamine and a three‐dimensional hydrogen‐bonded framework in 2,2,2‐trichloro‐N,N′‐bis(4‐chlorophenyl)ethane‐1,1‐diamine

In 2,2,2‐trichloro‐N,N′‐bis(4‐methoxyphenyl)ethane‐1,1‐diamine, C₁₆H₁₇Cl₃N₂O₂, molecules are linked into helical chains by N—H...O hydrogen bonds. Molecules of 2,2,2‐trichloro‐N,N′‐bis(4‐chlorophenyl)ethane‐1,1‐diamine, C₁₄H₁₁Cl₅N₂, are connected into a three‐dimensional framework by two independent Cl...Cl interactions and one C—H...Cl hydrogen bond.     

N,N′‐Bis(2‐methoxy­benzyl­idene) adducts of ethane‐1,2‐di­amine,propane‐1,3‐di­amine and butane‐1,4‐di­amine

We have isolated and crystallographically characterized the three homologous compounds N,N′‐bis(2‐methoxy­benzyl­idene)­ethane‐1,2‐di­amine (MeSalen), C₁₈H₂₀N₂O₂, N,N′‐bis(2‐methoxy­benzyl­idene)­propane‐1,3‐di­amine (MeSalpr), C₁₉H₂₂N₂O₂, and N,N′‐bis(2‐methoxy­benzyl­idene)­butane‐1,4‐di­amine (MeSalbu), C₂₀H₂₄N₂O₂. In contrast with MeSalpr, the mol­ecules of MeSalen and MeSalbu, which have an even number of methyl­ene units, have crystallographic symmetry. Comparing these methoxy‐substituted species with their hydroxy equivalents shows that the aryl rings rotate upon removal of the O—H⋯N hydrogen bonds. The packing of MeSalen and MeSalpr is controlled by C—H⋯π interactions, whereas that of MeSalbu has only van der Waals contacts.     

Novel one‐ and two‐dimensional ZnII coordination polymers based on a versatile 3,6‐bis(pyridin‐4‐yl)phenanthrene‐9,10‐dione ligand

Two new Zn^II coordination polymers, namely, catena‐poly[[dibromidozinc(II)]‐μ‐[3,6‐bis(pyridin‐4‐yl)phenanthrene‐9,10‐dione‐κ²N:N′]], [ZnBr₂(C₂₄H₁₄N₂O₂)]_n, (1), and poly[[bromido[μ₃‐10‐hydroxy‐3,6‐bis(pyridin‐4‐yl)phenanthren‐9‐olato‐κ³N:N′:O⁹]zinc(II)] hemihydrate], {[ZnBr(C₂₄H₁₅N₂O₂)]·0.5H₂O}_n, (2), have been synthesized through hydrothermal reaction of ZnBr₂ and a 60° angular phenanthrenedione‐based linker, i.e. 3,6‐bis(pyridin‐4‐yl)phenanthrene‐9,10‐dione, in different solvent systems. Single‐crystal analysis reveals that polymer (1) features one‐dimensional zigzag chains connected by weak C—H...π and π–π interactions to form a two‐dimensional network. The two‐dimensional networks are further stacked in an ABAB fashion along the a axis through C—H...O hydrogen bonds. Layers A and B comprise left‐ and right‐handed helical chains, respectively. Coordination polymer (2) displays a wave‐like two‐dimensional layered structure with helical chains. In this compound, there are two opposite helical –Zn–HL– chains [HL is 10‐hydroxy‐3,6‐bis(pyridin‐4‐yl)phenanthren‐9‐olate] in adjacent layers. The layers are packed in an ABAB sequence and are further connected through O—H...Br and O—H...O hydrogen‐bond interactions to form a three‐dimensional framework. In (1) and (2), the mutidentate L and HL ligands exhibits different coordination modes.     

Ni‐Catalyzed Chelation‐Assisted Direct Functionalization of Inert C—H Bonds

During the last two decades, impressive advancements have been achieved in transition metal‐catalyzed chelation‐assisted C—H functionalization reaction. While reactions in this field are still dominated by precious 4d or 5d metals (e.g., Pd, Rh, Ir), the 3d base metals (e.g., Ni, Co, Cu, Fe) have made significant headway partially due to their relatively large abundance, low cost, low toxicity as well as their occasionally occurred novel reactivity when compared to their noble cousins. This review will give a comprehensive summary on Ni‐catalyzed functionalization of inert C—H bonds assisted by chelation groups. For clarity, the content is classified by the newly formed chemical bonds, namely C—C, C—N, C—chalcogen and C—halogen bond formation.     

SO3H‐functionalized nano‐MGO‐D‐NH2: Synthesis,characterization and application for one‐pot synthesis of pyrano[2,3‐d]pyrimidinone and tetrahydrobenzo[b]pyran derivatives in aqueous media

An SO₃H‐functionalized nano‐MGO‐D‐NH₂ catalyst has been prepared by multi‐functionalization of a magnetic graphene oxide (GO) nanohybrid and evaluated in the synthesis of tetrahydrobenzo[b]pyran and pyrano[2,3‐d]pyrimidinone derivatives. The GO/Fe₃O₄ (MGO) hybrid was prepared via an improved Hummers method followed by the covalent attachment of 1,4‐butanesultone with the amino group of the as‐prepared polyamidoamine‐functionalized MGO (MGO‐D‐NH₂) to give double‐functionalized magnetic nanoparticles as the catalyst. The prepared nanoparticles were characterized to confirm their synthesis and to precisely determine their physicochemical properties. In summary, the prepared catalyst showed marked recyclability and catalytic performance in terms of reaction time and yield of products. The results of this study are hoped to aid the development of a new class of heterogeneous catalysts to show high performance and as excellent candidates for industrial applications.