Structure and magnetic properties of a hydroxo-bridged copper(II) distorted cubane stabilized via supramolecular hydrogen bonding with an ionic hexafluoroacetylacetonate

Tetranuclear [Cu(II)4(OH)4(aib)4)](hfac)4 (1; aib = 2-methyl-2-amino-4-iminopentane; hfac = hexafluoroacetylacetonate) forms from the reaction of aqueous ammonia and Cu(hfac)2.2H2O in acetone. The structure of 1 reveals that four noncoordinating hfac- counterions stabilize the distorted cubane complex via multiple H-bonding contacts. Magnetic susceptibility studies reveal that cubane-like 1 is best described as a pair of independent antiferromagnetically coupled dimers with g = 2.10 and J/kB = -298 K (207 cm(-1)) (H = -2JS1.S2).     

Enantioselective synthesis of endohedral metallofullerenes

Endohedral metallofullerenes are promising materials in biomedical and material sciences. In particular, they are of interest as agents for magnetic resonance imaging (MRI), photovoltaic devices, and semimetallic components. The synthesis of chiral endofullerenes represents one step further in the potential use of these carbon allotropes; however, this step has not been addressed so far. In this regard, enantiopure endofullerenes are expected to open new avenues in fields in which chirality is a key issue. Here, the synthesis and characterization of the first chiral endohedral metallofullerenes, namely, chiral bis-adducts of La@C(72), are reported. Eight optically active isomers were obtained by enantioselective 1,3-dipolar cycloaddition of a N-metalated azomethine ylide onto a non-isolated-pentagon rule metallofullerene derivative, La@C(72)(C(6)H(3)Cl(2)), catalyzed by a copper chiral complex. The chiral bis-adducts of La@C(72), isolated by nonchiral HPLC, showed optical purities as high as 98% as revealed by the remarkable positive or negative Cotton effects observed in the circular dichroic spectra.     

Synthesis and properties of Bingel-type methanofullerene-pi-extended-TTF diads and triads

Novel C(60)/pi-extended tetrathiafulvalene (exTTF) diads (12a-c) and triads [D(2)A (14a-c) and DA(2) (25, 27a-c)] have been synthesized by the Bingel cyclopropanation reaction of the respective exTTF-containing malonates and [60]fullerene. The reaction of exTTF-bismalonates with C(60) affords the respective C(60)-exTTF diads (26a-c) together with the triad C(60)-exTTF-C(60) (25, 27a-c) and a regioisomeric mixture of bisadducts (28b-c). Theoretical calculations (PM3) predict the favored geometry for triads 14a-c depending upon the orientation (up and down) of the 1,3-dithiole rings in the exTTFs, as well as the more stable regioisomers for the bisadducts 28. Cyclic voltammetry measurements reveal that C(60) and exTTF units do not intereact in the ground state. Compounds 26a-c and 27a-c are not electrochemically stable. A photoinduced electron transfer leading to the formation of the radical pair (C(60)(-)-exTTF(*+)) has been observed for compounds 14a-c.     

pH和盐类对非离子型表面活性剂所组成微乳液的异常流变性影响

以非离子型表面活性剂AEO~9、正十六烷、正己醇和水所组成的微乳液为对象, 研究盐和pH值对其粘度和流变性的影响, 得出它们在pH值为7时最小, 以及二价盐影响最大的结论, 正好与离子型微乳液结果相反, 为此进行了讨论。并从热效应和电导对其微观结构作了初步探索。     

Anion–π Catalysis on Carbon Nanotubes

Induced π acidity from polarizability is emerging as the most effective way to stabilize anionic transition states on aromatic π surfaces, that is, anion–π catalysis. To access extreme polarizability, we propose a shift from homogeneous toward heterogeneous anion–π catalysis on higher carbon allotropes. According to benchmark enolate addition chemistry, multi‐walled carbon nanotubes equipped with tertiary amine bases outperform single‐walled carbon nanotubes. This is consistent with the polarizability of the former not only along but also between the tubes. Inactivation by π‐basic aromatics and saturation with increasing catalyst concentration support that catalysis occurs on the π surface of the tubes. Increasing rate and selectivity of existing anion–π catalysts on the surface of unmodified nanotubes is consistent with transition‐state stabilization by electron sharing into the tubes, i.e., induced anion–π interactions. On pristine tubes, anion–π catalysis is realized by non‐covalent interfacing with π‐basic pyrenes.     

On–off switch of charge-separated states of pyridine-vinylene-linked porphyrin–C60 conjugates detected by EPR

The design, synthesis, and electronic properties of a new series of D–π–A conjugates consisting of free base (H₂P) and zinc porphyrins (ZnP) as electron donors and a fullerene (C₆₀) as electron acceptor, in which the two electroactive entities are covalently linked through pyridine-vinylene spacers of different lengths, are described. Electronic interactions in the ground state were characterized by electrochemical and absorption measurements, which were further supported with theoretical calculations. Most importantly, charge-transfer bands were observed in the absorption spectra, indicating a strong push–pull behavior. In the excited states, electronic interactions were detected by selective photoexcitation under steady-state conditions, by time-resolved fluorescence investigations, and by pump probe experiments on the femto-, pico-, and nanosecond time scales. Porphyrin fluorescence is quenched for the different D–π–A conjugates, from which we conclude that the deactivation mechanisms of the excited singlet states are based on photoinduced energy- and/or electron transfer processes between H₂P/ZnP and C₆₀, mediated through the molecular spacers. The fluorescence intensity decreases and the fluorescence lifetimes shorten as the spacer length decreases and as the spacer substitution changes. With the help of transient absorption spectroscopy, the formation of charge-separated states involving oxidized H₂P/ZnP and reduced C₆₀ was confirmed. Lifetimes of the corresponding charge-separated states, which ranged from ∼400 picoseconds to 165 nanoseconds, depend on the spacer length, the spacer substitution, and the solvent polarity. Interestingly, D–π–A conjugates containing the longest linkers did not necessarily exhibit the longest charge-separated state lifetimes. The distances between the electron donors and the acceptors were calculated by molecular modelling. The longest charge-separated state lifetime corresponded to the D–π–A conjugate with the longest electron donor–acceptor distance. Likewise, EPR measurements in frozen media revealed charge separated states in all the D–π–A conjugates investigated. A sharp peak with g values ∼2.000 was assigned to reduced C₆₀, while a broader, less intense signal (g ∼ 2.003) was assigned to oxidized H₂P/ZnP. On–off switching of the formation and decay of the charge-separated states was detected by EPR at 77 K by repeatedly turning the irradiation source on and off.     

Eco-friendly methodology to prepare N-heterocycles related to dihydropyridines: microwave-assisted synthesis of alkyl 4-arylsubstituted-6-chloro-5-formyl-2-methyl-1,4-dihydropyridine-3-carboxylate and 4-arylsubstituted-4,7-dihydrofuro[3,4-b]pyridine-2,5(1H,3H)-dione

Here we describe the efficient synthesis of alkyl 4-arylsubstituted-6-chloro-5-formyl-2-methyl-1,4-dihydropyridine-3-carboxylates and 4-arylsubstituted-4,7-dihydro-furo[3,4-b]pyridine-2,5(1H,3H)-diones via microwave-accelerated reaction of alkyl 4-arylsubstituted-2-methyl-6-oxo-1,4,5,6-tetrahydro-3-pyridinecarboxylates with the appropriate reagents. This eco-friendly approach to these valuable dihydropyridine derivatives does not involve the harsh or highly contaminating conditions common in classical heating and offers a reduction or even elimination of solvent use and recovery, simplification of the work-up procedures, facility of scale up, and low energy consumption, in addition to moderate to higher yields.     

Hydrogen-bonding motifs in fullerene chemistry

The combination of fullerenes and hydrogen-bonding motifs is a new interdisciplinary field in which weak intermolecular forces allow modulation of one-, two-, and three-dimensional fullerene-based architectures and control of their function. This Minireview aims to extend the scope of fullerene chemistry to a truly supramolecular level from which unprecedented architectures may evolve. It is shown that electronic communication in C(60)-based hydrogen-bonded donor-acceptor ensembles is at least as strong as that found in covalently connected systems and that hydrogen-bonding fullerene chemistry is a versatile concept for the construction of functional ensembles.