Heterogeneous Gold Nanoparticle-Based Catalysts for the Synthesis of Click-Derived Triazoles via the Azide-Alkyne Cycloaddition Reaction

A supported gold nanoparticle-catalyzed strategy has been utilized to promote a click chemistry reaction for the synthesis of 1,2,3-triazoles via the azide-alkyne cycloaddition (AAC) reaction. While the advent of effective non-copper catalysts (i.e., Ru, Ag, Ir) has demonstrated the catalysis of the AAC reaction, additional robust catalytic systems complementary to the copper catalyzed AAC remain in high demand. Herein, Au nanoparticles supported on Al2O3, Fe2O3, TiO2 and ZnO, along with gold reference catalysts (gold on carbon and gold on titania supplied by the World Gold Council) were used as catalysts for the AAC reaction. The supported Au nanoparticles with metal loadings of 0.7–1.6% (w/w relative to support) were able to selectively obtain 1,4-disubstituted-1,2,3-triazoles in moderate yields up to 79% after 15 min, under microwave irradiation at 150 °C using a 0.5–1.0 mol% catalyst loading through a one-pot three-component (terminal alkyne, organohalide and sodium azide) procedure according to the “click” rules. Among the supported Au catalysts, Au/TiO2 gave the best results.

Zr-Catalyzed Microwave Assisted Functionalization of Alkyne and Nitroalkene

Water and zirconium(IV) as catalyst were found to be effective in the transformation of terminal aromatic alkyne to aromatic methyl ketone in the microwave. This terminal alkyne hydration reaction proceeded in excellent yield with Zr(cp)2Cl2. The reaction was moved efficiently in presence of electron donating or electron withdrawing substituent on aromatic ring. An eco-friendly synthesis of aldehyde by oxidative cleavage of nitroalkene was developed with Zr(cp)2Cl2 catalyst and water in microwave.

Synthesis of Zwitter-Ionic Conjugate of Nido-Carborane with Cholesterol

9-HC≡CCH2Me2N-nido-7,8-C2B9H11, a previously described carboranyl terminal alkyne, was used for the copper(I)-catalyzed azide-alkyne cycloaddition with azido-3β-cholesterol to form a novel zwitter-ionic conjugate of nido-carborane with cholesterol, bearing a 1,2,3-triazol fragment. The conjugate of nido-carborane with cholesterol, containing a charge-compensated group in the linker, can be used as a precursor for the preparation of liposomes for BNCT (Boron Neutron Capture Therapy). The solid-state molecular structure of a nido-carborane derivative with the 9-Me2N(CH2)2Me2N-nido-7,8-C2B9H11 terminal dimethylamino group was determined by single-crystal X-ray diffraction.

A Family of Externally-Functionalised Coordination Cages

New synthetic routes are presented to derivatives of a (known) M8L12 cubic coordination cage in which a range of different substituents are attached at the C4 position of the pyridyl rings at either end of the bis(pyrazolyl-pyridine) bridging ligands. The substituents are (i) –CN groups (new ligand LCN), (ii) –CH2OCH2–CCH (containing a terminal alkyne) groups (new ligand LCC); and (iii) –(CH2OCH2)3CH2OMe (tri-ethyleneglycol monomethyl ether) groups (new ligand LPEG). The resulting functionalised ligands combine with M2+ ions (particularly Co2+, Ni2+, Cd2+) to give isostructural [M8L12]16+ cage cores bearing 24 external functional groups; the cages based on LCN (with M2+ = Cd2+) and LCC (with M2+ = Ni2+) have been crystallographically characterised. The value of these is twofold: (i) exterior nitrile or alkene substituents can provide a basis for further synthetic opportunities via ‘Click’ reactions allowing in principle a diverse range of functionalisation of the cage exterior surface; (ii) the exterior –(CH2OCH2)3CH2OMe groups substantially increase cage solubility in both water and in organic solvents, allowing binding constants of cavity-binding guests to be measured under an increased range of conditions.

2,2-Bis(phenylselanyl)-1-(p-tolyl)vinyl 2-Oxo-2-(p-tolyl)acetate

2,2-Bis(phenylselanyl)-1-(p-tolyl)vinyl 2-oxo-2-(p-tolyl)acetate was synthesized via the reaction of p-tolylacetylene with diphenyl diselenide and benzoyl peroxide in benzene under atmospheric conditions. The molecular structure of the synthesized compound was evaluated using single-crystal X-ray analysis and spectral analyses. The process reported here provides a rare example of the direct and selective transformation of a terminal alkyne to the corresponding geminal diseleno-substituted alkene.