A unique ‘ON-OFF-ON’ switch with two perturbations at two different concentrations of Ag

The dipod 1,2-bis(8-quinolinoxymethyl)benzene 3 and tetrapod 1,2,4,5-tetrakis(8-quinolinoxymethyl)benzene 4 show two perturbations in fluorescence with Ag⁺, (i) fluorescence quenching with <1.0 equiv of AgNO₃ at λ_max 395 nm and (ii) fluorescence enhancement at λ_max 500 nm with >3 equiv of AgNO₃. This ‘ON-OFF-ON’ switching of 3 and 4 in comparison with simultaneous fluorescence quenching and enhancement in the case of 8-methoxyquinoline 1 and the tripod 1,3,5-trimethyl-2,4,6-tris(8-quinolinoxymethyl)benzene 2 point to the unique role of molecular architectures arising due to the number and spatial positions of quinoline units in the fluorescence behaviour of an 8-alkoxyquinoline moiety towards Ag⁺.     

Synthesis and properties of 4,4′-bipyridine based tetracationic carbazolophanes

The precyclophane derived from 3,6-bis(bromomethyl)-9-ethylcarbazole and 5 equiv of 4,4′-bipyridine underwent macrocyclization on quaternization with various dibromides including 3,6-bis(bromomethyl)-9-ethylcarbazole to give carbazole-paraquat, self-complementary, cyclophanes revealing distinct charge-transfer and electrostatic interactions. The macrocyclic carbazolophane 1 was also obtained by a one-pot quaternization technique using equimolar amounts of 3,6-bis(bromomethyl)-9-ethylcarbazole and 4,4′-bipyridine.     

Three different fluorescent responses to transition metal ions using receptors based on 1,2-bis- and 1,2,4,5-tetrakis-(8-hydroxyquinolinoxymethyl)benzene

The dipod 1,2-bis(8-hydroxyquinolinoxymethyl)benzene (3) and tetrapod 1,2,4,5-tetrakis(8-hydroxyquinolinoxymethyl)benzene (5) have been synthesized through nucleophilic substitution of respective 1,2-bis(bromomethyl)benzene (2) and 1,2,4,5-tetra(bromomethyl)benzene (4) with 8-hydroxyquinoline (1). For comparison, 1,3,5-tris(8-hydroxyquinolinoxymethyl)benzene derivatives (7a and 7b) have been obtained. The complexation behavior of these podands towards Ag⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, and Cd²⁺ metal ions has been investigated in acetonitrile by fluorescence spectroscopy. The sterically crowded 1,2,4,5-tetrapod 5 displays unique fluorescence ‘ON-OFF-ON’ switching through fluorescence quenching (λ_max 395 nm, switch OFF) with <1.0 equiv of Ag⁺ and fluorescence enhancement (λ_max 495 nm, switch ON) with >3 equiv Ag⁺ and can be used for estimation of two different concentrations of Ag⁺ at two different wavelengths. The addition of Cu²⁺, Ni²⁺, and Co²⁺ metal ions to tetrapod 5 causes fluorescence quenching, i.e., ‘ON-OFF’ phenomena at λ_max 395 nm for <10 μM (1 equiv) of these ions but addition of Zn²⁺ and Cd²⁺ to tetrapod 5 results in fluorescence enhancement with a gradual shift of λ_em from 395 to 432 and 418 nm, respectively. Similarly, dipod 3 behaves as an ‘ON-OFF-ON’ switch with Ag⁺, an ‘ON-OFF’ switch with Cu²⁺, and an ‘OFF-ON’ switch with Zn²⁺. The placement of quinolinoxymethyl groups at the 1,3,5-positions of benzene ring in tripod 7a-b leads to simultaneous fluorescence quenching at λ_max 380 nm and enhancement at λ_max 490 nm with both Ag⁺ and Cu²⁺. This behavior is in parallel with 8-methoxyquinoline 8. The rationalization of these results in terms of metal ion coordination and protonation of podands shows that 1,2 placement of quinoline units in tetrapod 5 and dipod 3 causes three different fluorescent responses, i.e., ‘ON-OFF-ON’, ‘ON-OFF’, and ‘OFF-ON’ due to metal ion coordination of different transition metal ions and 1, 3, and 5 placement of three quinolines in tripod 7, the protonation of quinolines is preferred over metal ion coordination. In general, the greater number of quinoline units coordinated per metal ion in 5 compared with the other podands points to organization of the four quinoline moieties around metal ions in the case of 5.     

Conformational behavior of dithia[n.3.3](1,3,5)cyclophanes and dithia[n.3.3](1,2,6)cyclophanes

The conformational behavior of a series of crown-fused dithia[n.3.3](1,2,6)cyclophanes (126-CPs) and dithia[n.3.3](1,3,5)cyclophanes (135-CPs) was investigated by variable-temperature ¹H and ¹³C NMR spectroscopy, X-ray crystallography and density functional theory (DFT) calculations. Single crystal X-ray structure analysis showed that two thia-bridges in 126-CPs adopted a pseudochair-pseudochair (cc) conformation and the cyclophane decks underwent a ring-tilting motion in the case of [10.3.3](1,2,6)cyclophane (1a). In contrast, the thia-bridges in 135-CPs took both cc and pseudoboat-pseudochair (bc) conformations, and the ring-tilting process was also found in [10.3.3](1,3,5)cyclophane (2a). Variable temperature ¹H NMR study revealed that there was no wobbling-motion for two thia-bridges in 126-CPs while thia-bridges in 135-CPs experienced a wobbling-process with a conformational barrier of 9.21 and 8.80 kcal mol⁻¹, respectively, for 2a and [13.3.3](1,3,5)cyclophane (2b). DFT calculations for the two cyclophanes series revealed that 126-CPs preferred a cc conformation which was consistent with the experimental observation; similarly, 135-CPs took a preferential cc conformation, agreeing with 2a having a predominant cc conformer (cc:bc ratio=70:30), but not 2b having a predominant bc conformer (cc:bc ratio=15:85) in the solid state.     

The rotation of pentaphenylphenyl groups and their terminal phenyl groups: a variable-temperature H NMR study on an albatrossene and a three-bladed molecular propeller

Dynamic NMR of 1-phenylethynyl-3,5-bis(pentaphenylphenyl)benzene (1) and 1,3,5-tris(pentaphenylphenyl)benzene (2) allows us to determine two rotational barriers for each compound. For 1, a first process exhibits ΔG^‡ = 39.2 kJ/mol followed by a second one with a ΔG^‡ value of 69.9 kJ/mol. Two processes with similar rotational barriers are found for 2 (70.9 and 75.3 kJ/mol). Motional processes which can be related to these barriers are 60° and 180° rotations of the pentaphenylphenyl units about the single bond with the core benzene ring and rotation of the terminal phenyl rings of the pentaphenylphenyl units. The results are discussed considering the consequences of these processes on the NMR spectra.     

Photochemical formation of [4.4.4](1,3,5)cyclophanes from 1,3,5-tris(3-phenylpropenoyl)benzenes

Irradiation of 1,3,5-tris(3-phenylpropenoyl)benzene (1a) yields in solution a dimer 2a by a threefold head-to-head/anti [2π+2π]cycloaddition. The stereochemistry of this [4.4.4](1,3,5)cyclophane was determined by ¹H and ¹³C NMR studies including NOE measurements and a calculation of the AA′MM′ spin pattern of the methine protons. In contrast to the solution photochemistry, which is presumably controlled by the arrangement of an excimer, the irradiation in the crystalline state leads by a topochemical control to a dimer 3a, which contains a single four-membered ring.     

New binucleating ligand with two [P,S] chelation pockets on a single phenyl ring: Syntheses and X-ray structures of 1,4-bis(diphenylphosphino)-2,5-difluoro-3,6-bis(methylthio)benzene and of bimetallic complex (CO)3Fe(μ-[(PPh2)(SMe)C6F2(SMe)(PPh2)])Fe(CO)3

Double deprotonations of 1,4-dibromo-2,5-difluorobenzene with LDA (2 equiv., T < −90 °C) generate a reasonably stable organodilithium intermediate. Quenching this reaction mixture with chlorophosphines ClPR₂ produce p-bis(phosphino)benzenes R₂P-C₆Br₂F₂-PR₂ (R = Ph, 4a; R = ⁱPr, 4b). Facile lithium-bromine exchange occurs upon exposure of 4a to BuLi (2 equiv., −80 °C), leading to the generation of another organodilithium intermediate. Addition of MeS-SMe (2 equiv.) to such reaction mixtures gives 1,4-bis(diphenylphosphino)-2,5-difluoro-3,6-bis(methylthio)benzene (2). Compound 2 is the first example of a neutral binucleating ligand featuring the [P,S] chelating sites on the opposite sides of a single phenyl ring. Compound 4b does not undergo the analogous transformation when subjected to the same conditions (2BuLi/2MeS-SMe). Addition of 2 to Fe(CO)₅/2(Me₃NO · 2H₂O) reaction mixtures led to the isolation of the bimetallic complex {(CO)₃Fe[P,S]-C₆F₂-[P,S]Fe(CO)₃} (3), ([P,S] represents the chelating pockets formed by adjacent -PPh₂ and -SMe groups). All of the new compounds were characterized by spectroscopic and analytical techniques (multinuclear NMR, mass-spectrometry, and/or elemental analysis). In addition, compounds 2 and 3 were characterized via single crystal X-ray diffraction methods.     

[2 + 2] Photodimerization and photopolymerization of diphenylhexatriene crystals utilizing perfluorophenyl-phenyl stacking interactions

Irradiation of the crystal of 1-perfluorophenyl-6-phenyl-1,3,5-hexatriene (1), the 1:1 cocrystal of 1,6-diphenyl-1,3,5-hexatriene (2) and 1,6-bis(perfluorophenyl)-1,3,5-hexatriene (3) (2/3), and crystal 3 gave a mixture of dimer, trimer and higher oligomers that was soluble in common organic solvents. The highest molecular weight was 5000-8000 (the degree of polymerization = 15-20). The order of reactivity was 1 > 2/3 ? 3. The reaction of 1 was relatively efficient compared to typical organic crystals. The conversion reached 100% after 3 h irradiation. In each case, the regio- and stereoselectivity in the photodimerization was high, whereas in the formation of trimer and higher oligomers, the selectivity was much lower. The main dimer was spectroscopically identified to be the face-to-face dimer formed by the [2 + 2] cycloaddition at the 1,2-position of the triene double bonds. The photoproducts from 1 and 2/3 were amorphous, as evidenced by powder X-ray diffraction and polarizing optical microscopy. This is probably due to the nonplanar and bulky structures of the cyclobutane products. The photodimerization and polymerization are considered to be non-topochemical reactions.     

Design and synthesis of ninhydrin-based cyclophanes as potential neutral receptors for quaternary ammonium cations

Four ninhydrin-based cyclophanes 4a, 4b, 6a, and 6b were designed and synthesized. Two rectangular type cyclophanes (4a and 4b) and two square type cyclophanes (6a and 6b) were prepared in 8-43% yields.     

The stereodynamics of 3,5-bis(trifluoromethylsulfonyl)-1,3,5-oxadiazinane and 1,3,5-tris(trifluoromethylsulfonyl)-1,3,5-triazinane—an experimental and theoretical study

Multinuclear dynamic NMR spectroscopy of 3,5-bis(trifluoromethylsulfonyl)-1,3,5-oxadiazinane (3) revealed the existence of two conformers with differently oriented CF₃ groups with respect to the ring, and two dynamic processes: ring inversion and restricted rotation about the N-S bond. Two transition states connecting the two conformers and corresponding to clockwise and counterclockwise rotations about the N-S bond were found; the calculated activation barriers of about 12 kcal/mol are in excellent agreement with those measured experimentally for the related molecule 1,3,5-tris(trifluoromethylsulfonyl)-1,3,5-triazinane (1). X-ray analysis proved the existence of the symmetric isomer of 3, which is the minor isomer in solutions but the only one in the crystal due to packing effects. The normal Perlin effect (JCH_ax<JCH_eq) was observed for 2(6)-CH₂ in 3, whereas the reversed Perlin effect was found for the 4-CH₂ group in 3 as well as for all CH₂ groups in 1 both experimentally and theoretically. The latter effect in compounds 1, 3, and 1-(methylsulfonyl)-3,5-bis(trifluoromethylsulfonyl)-1,3,5-triazinane (2) can be considered as a genuine reverse Perlin effect since larger values of ¹J_CH are observed for longer C-H bonds.     

Oxa-bridged cyclophanes featuring thieno[2,3-b]thiophene and C2-symmetric binol or bis-naphthol rings: synthesis, structures, and conformational studies

Oxa-bridged cyclophanes 4/6 and 8/10 featuring thieno[2,3-b]thiophene ring and binol or bis-naphthol have been synthesized. The structures are assigned by 2D NMR data and the identity of 4 is also independently established by a single X-ray crystallography. From dynamic NMR analysis, the Arrhenius energy of activation ΔG^# for bridge inversions in 4 and 6 was calculated to be 15.3 and 12.9 kcal/mol, respectively. A higher ΔG^# for 4, relative to the ester free 6 is attributable to the steric compression stemming from C2/C5 ester substituents to the bridge inversion processes. While the methylene bridges undergo inversion in 4 and 6, the naphthyl-naphthyl pseudo-rotation appears to be restricted even at higher temperatures. This is supported by retention of the optical purity of the chiral (−) 4 under thermal condition. For the case of bis-naphthol cyclophane 8, we observed the flipping of both the -OCH₂- and the naphthyl-CH₂-naphthyl bridges with ΔG^# of ca. 11.4 kcal/mol. However, the ester free cyclophane 10 remained conformationally mobile even at −55 °C and its ΔG^# was assumed to be <11.4 kcal/mol. The presence of an extra -CH₂- linker in bis-naphthol cyclophanes 8/10 renders them relatively more conformationally mobile compared to binol cyclophanes 4/6, possessing a rigid naphthyl-naphthyl geometry.     

Interaction of copper(II) and palladium(II) with linked 2,2′-dipyridylamine derivatives: Synthetic and structural studies

Interaction of copper(II) salts with 2,2′-dipyridylamine (1), N-cyclohexylmethyl-2,2′-dipyridylamine (2), di-2-pyridylaminomethylbenzene (3), 1,2-bis(di-2-pyridylaminomethyl)-benzene (4), 1,3-bis(di-2-pyridylaminomethyl)benzene (5), 1,4-bis(di-2-pyridylaminomethyl)benzene (6), 1,3,5-tris(di-2-pyridylaminomethyl)benzene (7) and 1,2,4,5-tetrakis(di-2-pyridylaminomethyl)benzene (8) has yielded the following complexes: [Cu(2)(μ-Cl)Cl]₂, [Cu(3)(μ-Cl)Cl]₂ · H₂O, [Cu₂(4)(NO₃)₄], [Cu₂(5)(NO₃)₄] · 2CH₃OH, [Cu₂(6)(CH₃OH)₂(NO₃)₄], [Cu₄(8)](NO₃)₄] · 4H₂O while complexation of palladium(II) with 1, 4, 5 and 6 gave [Pd(1)₂](PF₆)₂ · 2CH₃OH, [Pd₂(4)Cl₄], [Pd₂(4)(OAc)₄], [Pd₂(5)Cl₄], [Pd₂(6)Cl₄] and [Pd₂(6)(OAc)₄] · CH₂Cl₂, respectively. X-ray structures of [Cu(2)(μ-Cl)Cl]₂, [Cu(3)(μ-Cl)Cl]₂ · 2C₂H₅OH, [Cu₂(6)(CH₃OH)₂(NO₃)₄], [Pd(1)₂](PF₆)₂ · 2CH₃OH, [Pd₂(4)(OAc)₄] · 4H₂O and [Pd₂(6)(OAc)₄] · 2CH₂Cl₂ are reported. In part, the inherent flexibility of the respective ligands has resulted in the adoption of a diverse range of coordination geometries and lattice arrangements, with the structures of [Pd₂(4)(OAc)₄] · 4H₂O and [Pd₂(6)(OAc)₄] · 2CH₂Cl₂, incorporating the isomeric ligands 4 and 6, showing some common features. Liquid–liquid (H₂O/CHCl₃) extraction experiments involving copper(II) and 1–3, 5, 7and 8 show that the degree of extraction depends markedly on the number of dpa-subunits (and concomitant lipophilicity) of the ligand employed with the tetrakis-dpa derivative 8 acting as the most efficient extractant of the six ligand systems investigated.     

Synthesis of novel multidentate carbohydrate-triazole ligands

Cu(I)-catalyzed 1,3-dipolar cycloaddition (click reaction) of 1 mol equiv of N,N′-di-prop-2-ynyl-phthalamide (1a), N,N′-di-prop-2-ynyl-isophthalamide (1b), and pyridine-2,6-dicarboxylic acid bis-prop-2-ynylamide (1c), respectively with 2 mol equiv of 2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl azide (2a), 2-azidoethyl 2,3,4,6-tetra-O-acetyl-β-d-glucopyranoside (2b), and 2-azidoethyl 2,3,4,6-tetra-O-acetyl-α-d-mannopyranoside (2c), respectively, afforded the corresponding bis-cycloadducts 3-5, containing two 1,2,3-triazole moieties each, in 38-76% yield. Reaction of 1 mol equiv of 2c with 1 mol equiv of 1c under otherwise identical conditions gave the mono-cycloadduct 6, containing one 1,2,3-triazole and one 2-propynylamide moiety, in 77% yield. Reaction of 6 with 2a afforded 7, containing two different sugar moieties, in 67% yield.     

The conversion of 2-(4-chloro-5H-1,2,3-dithiazolylideneamino)benzonitriles into 3-aminoindole-2-carbonitriles using triphenylphosphine

2-(4-Chloro-5H-1,2,3-dithiazolylideneamino)benzonitrile 1a reacts with triphenylphosphine (4 equiv) in the presence of water (2 equiv) to afford anthranilonitrile 2a, 3-aminoindole-2-carbonitrile 3a and (2-cyanoindol-3-yl)iminotriphenylphosphorane 4a, together with triphenylphosphine sulfide and oxide. The use of polymer bound triphenylphosphine provides cleaner reaction mixtures. 2-(4-Chloro-5H-1,2,3-dithiazolylideneamino)-4,5-dimethoxybenzonitrile 1h does not give the corresponding indole on treatment with triphenylphosphine but gives 6,7-dimethoxyquinazoline-2-carbonitrile 5 (15%) and 2-cyano-4,5-dimethoxy cyanothioformanilide 6 (36%). A total of seven new 3-aminoindole-2-carbonitriles 3a-g are prepared and fully characterised.     

N-heterocyclic carbene coordinated gallanes and chlorogallanes

The preparation of the N-heterocyclic carbene coordinated gallium complexes [GaH₃(IXy)] (1), [GaH₃(IDipp)] (2), [GaClH₂(IMes)] (3) and [GaCl₂H(IMes)] (4), where IXy = 1,3-bis(2,6-dimethylphenyl)imidazol-2-ylidene, IDipp = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene and IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene, are reported. All four complexes have been characterised by ¹H, ¹³C NMR and IR spectroscopy and, for complexes 2, 3 and 4, single crystal X-ray structure determination. These compounds represent some of the most thermally stable molecular gallium hydrides known, with 4 being the most thermally stable gallium hydride reported (dec. 274 °C). These remarkable thermal stabilities translate to significant aerobic stability such that all four compounds may be handled in dry air without significant decomposition. Compounds 2, 3 and 4 exist as distorted tetrahedra in the solid state with gallium to carbene C-donor bonds that shorten with increasing Lewis acidity of the gallium centre. Compound 2 co-crystallizes with 1 equiv. of 2,6-diisopropylphenylaniline and exhibits several weak intermolecular bonding interactions in the solid-state.     

Synthesis of novel lariat azathia crown macrocycles containing two triazole rings and bis crown macrocycles containing four triazole rings

The 13-hydroxy macrocycles 7a-d were prepared in 40-50% yields by the condensation of 1,ω-bis(4-amino-1,2,4-triazol-3-ylsulfany)alkanes 2a-d with 1,3-bis(2-formyphenoxy)-2-propanol (9). Acylation of 7a-d with 2-chloroacetylchloride gave the corresponding esters 11a,b. Amination of 11a,b with different amines in acetone furnished exclusively the target lariat macrocycles 12a,b and 13 in 60-70% yields. Reaction of 2 equiv. of the macrocycles 11a,b with 1 equiv. of piperazine afforded the novel bis macrocyles 14a,b in 50-60% yields. Reduction of 7a-d with NaBH₄ afforded the corresponding 13-hydroxyazathia crown ethers 15a-d in 65-70% yields.     

Synthesis and crystal structures of three novel coordination polymers generated from AgCN and AgSCN with flexible N-donor ligands

The solvothermal reactions of AgX (X = CN, SCN) with mbix [mbix = 1,3-bis(imidazole-l-yl-methyl)benzene] or bix [bix = 1,4-bis(imidazole-l-yl-methyl)benzene] afforded the polymers [AgCN(mbix)]_n (1), [(AgCN)₄(bix)₂]_n (2) and [(AgSCN)₂(mbix)]_n (3). They were all characterized by infrared spectroscopy, elemental analysis and X-ray single-crystal analysis. The structure of 1 contains a 3-fold-interpenetrated 2D network, while that of 2 exhibits 2-fold parallel interpenetration. There is no interpenetration observed in 3. Compounds 2 and 3 show 3D supramolecular structures built from 2D networks through weak π ? π interactions. The photoluminescent properties of the present compounds were also investigated.     

Tautomerism, structure and properties of 1,1′,1″-(2,4,6-trihydroxybenzene-1,3,5-triyl)triethanone

According to computational predictions 1,1′,1″-(2,4,6-trihydroxybenzene-1,3,5-triyl)triethanone (triacetylphloroglucinol) (TTT, form a) can exist in five tautomeric forms, among which 2,4,6-tris(1-hydroxyethylidene)-1,3,5-cyclohexanetrione (form e) exhibits thermodynamic stability comparable to that of form a. X-ray investigations reveal that the compound exists in form a in the crystalline solid phase. Analysis of the arrangement of atoms involved in the three intramolecular H-bonds, responsible for the stabilization of tautomer a by 55.4 kcal/mol, suggests that there could be fast H atom (proton) transfer within the hydrogen bonds, bringing about the transformation of a into e and vice versa. Such an effect could explain the unique behaviour and spectral properties of TTT in solutions.     

Novel synthesis of 1-aryl-1-trifluoromethylallenes

3,3-Bis(phenylthio)-1,1,1,2,2-pentafluorobutane 1 was reacted with aryllithium reagents (6 equiv) in ether at low to room temperature for 1-6 h to provide 2-aryl-1,1,1-trifluoro-3-phenylthio-2-butene 2 in 80-96% yields. Bromination of 2 with NBS in acetonitrile at reflux for 1-7 h afforded the corresponding allylic bromides 3 in 61-96% yields. Treatment of 3 with MCPBA (1.5 equiv) in methylene chloride at reflux temperature for 1-12 h resulted in the formation of 1-aryl-1-trifluoromethylallenes 4 in 74-96% yields.     

A new type of chiral porphyrin: Organopalladium porphyrins with chiral chelating diphosphine ligands

Peripherally palladated Ni(II) porphyrins have been prepared using enantiopure chiral chelating diphosphines as supporting ligands on the attached Pd(II) fragment. Both enantiomers of the following complexes have been obtained in good yields, using oxidative addition of the bromoporphyrin starting material 5-bromo-10,20-diphenylporphyrinatonickel(II) (NiDPPBr (1)) to the [Pd⁰L] complex generated in situ from Pd₂dba₃ and the chiral ligand L: [PdBr(NiDPP)(CHIRAPHOS)] (2a,b) [CHIRAPHOS = 2,3-bis(diphenylphosphino)butane], [PdBr(NiDPP)(Tol-BINAP)] (3a,b) [Tol-BINAP) = 2,2′-bis(di-p-tolylphosphino)-1,1′-binaphthyl] and [PdBr(NiDPP)(diphos)] [diphos = 1,2-bis(methylphenylphosphino)benzene] (4a,b). The induced asymmetry in the porphyrin was readily detected by ¹H NMR and CD spectroscopy. The porphyrin chiroptical properties are strongly dependent upon the structure of the chiral ligand, such that a monosignate CD signal, and symmetric and asymmetric exciton couplets were observed for 4a, 2b, and 3a,b, respectively.