Multifunctionalization of dendrimers through orthogonal transformations

A straightforward methodology for the synthesis of multifunctionalized dendrimers that is based on an orthogonal functionalization strategy has been developed. Polyamide-based dendrimers that possess both a single aldehyde and a single azide moiety on their periphery have been synthesized by using a convergent synthetic strategy. These dendrimers can be functionalized quantitatively with small organic and biological molecules that contain hydrazide and/or alkyne groups in which each functional moiety is completely specific for its complementary motif. This orthogonal functionalization strategy has the potential to be used to synthesize multifunctional dendrimers for a variety of applications, which range from targeted biological delivery vehicles to optical materials.     

Combinatorial transition-metal catalysis: mixing monodentate ligands to control enantio-, diastereo-, and regioselectivity

This review focuses on a new approach to combinatorial homogeneous transition-metal catalysis which goes beyond the traditional parallel preparation of modular ligands. It is based on the use of mixtures of monodentate ligands L(a) and L(b), which upon exposure to a transition metal (M) form not only the two homocombinations [ML(a)L(a)] and [ML(b)L(b)], but also the heterocombination [ML(a)L(b)]. If the latter is more reactive and selective than the homocombinations, an improved catalyst system is formed without the need to synthesize new ligands. Thus, the control of enantio,- diastereo-, and regioselectivity is possible.     

Highly Stable Copper(I)–Thiacalix[4]arene-Based Frameworks for Highly Efficient Catalysis of Click Reactions in Water

Environmentally friendly metal–organic frameworks (MOFs) have gained considerable attention for their potential use as heterogeneous catalysts. Herein, two Cu^I-based MOFs, namely, [Cu₄Cl₄L] ⋅ CH₃OH ⋅ 1.5 H₂O ( 1-Cl ) and [Cu₄Br₄L] ⋅ DMF ⋅ 0.5 H₂O ( 1-Br ), were assembled with new functionalized thiacalix[4]arenes (L) and halogen anions X⁻ (X=Cl and Br) under solvothermal conditions. Remarkably, catalysts 1-Cl and 1-Br exhibit great stability in aqueous solutions over a wide pH range. Significantly, MOFs 1-Cl and 1-Br , as recycled heterogeneous catalysts, are capable of highly efficient catalysis for click reactions in water. The MOF structures, especially the exposed active Cu^I sites and 1D channels, play a key role in the improved catalytic activities. In particular, their catalytic activities in water are greatly superior to those in organic solvents or even in mixed solvents. This work proposes an attractive route for the design and self-assembly of environmentally friendly MOFs with high catalytic activity and reusability in water.     

Ethylene and Ethylene/Propylene Polymerization Behavior of Bis(phenoxy‐imine) Zr and Hf Complexes with Perfluorophenyl Substituents

The catalytic properties of bis(phenoxy‐imine) Zr and Hf complexes incorporating perfluorophenyl groups with methylaluminoxane were investigated. The fluorinated complexes produced far higher‐molecular‐weight polyethylenes and ethylene/propylene copolymers with increased activities compared with the non‐fluorinated congeners. Moreover, the fluorinated complexes displayed a higher incorporation ability for propylene.

Structures of complexes 1 – 4 .     

Novel transition-metal-free heterogeneous epoxidation catalysts discovered by means of high-throughput experimentation

Various transition-metal-free oxides have been studied as catalysts for the epoxidation of cyclooctene with hydrogen peroxide by means of high-throughput experimentation. Different boron, aluminium, and gallium oxides were prepared according to various synthesis methods. A number of pure aluminium and gallium oxides showed very good catalytic performances, while the results obtained with boron oxides or mixed oxides were less positive. The best results were obtained with a gallium oxide catalyst, which gave an epoxide yield of 71 % and a selectivity of 99 % after reaction for 4 h at 80 degrees C. Gallium oxides had not been reported previously as active epoxidation catalysts. The use of high-throughput experimentation proved useful both for discovering new active catalysts and for identifying a number of relationships between the synthesis conditions and the catalytic properties of the transition-metal-free oxides.     

Double Cu-Catalyzed Direct Csp3−H Azidation/CuAAC Reaction: A Direct Approach towards Demanding Triazole Conjugates

The first one-pot procedure for the double copper(I)-catalyzed oxidative Csp³−H azidation–CuAAC process, implying unstable azide intermediates and easy-to-remove reagents under water-tolerant conditions, is presented. The combination of tert-butyl hydroperoxide as oxidant and TMSN₃ as azide source for the C−H bond azidation, which produces harmless side-products such as tBuOH and H₂O, probed to be perfectly compatible with the following cycloaddition step. Highly demanding 1,2,3-triazoles could be then directly obtained in good overall yields by extraction or simple crystallization, thus avoiding chromatography purifications. The potential of this methodology, has also being highlighted by the successful reaction of alkynes presenting interesting complex biological moieties based for example on biotin, DNA base or cinchona alkaloid units.     

Sonogashira反应研究的最新进展

对Sonogashira反应的最新研究进展作了综述. 详细地介绍了Sonogashira 反应的最新优化、联串化、绿色化以及非Pd催化的Sonogashira反应等, 同时还综述了Sonogashira反应的机理研究.