Hydrosilylation of Terminal Alkynes Catalyzed by an Air-Stable Manganese-NHC Complex.

In recent years, catalysis with base metal manganese has received a significant amount of interest. Catalysis with manganese complexes having N-heterocyclic carbenes (NHCs) is relatively underdeveloped in comparison to the extensively investigated manganese catalysts possessing pincer ligands (particularly phosphine-based ligands). Herein, we describe the synthesis of two imidazolium salts decorated with picolyl arms (L1 and L2) as NHC precursors. Facile coordination of L1 and L2 with MnBr(CO)5 in the presence of a base resulted in the formation manganese(I)-NHC complexes (1 and 2) as an air-stable solid in good isolated yield. Single-crystal X-ray analysis revealed the structure of the cationic complexes [Mn(CO)3(NHC)][PF6] with tridentate N,C,N binding of the NHC ligand in a facile fashion. Along with a few known manganese(I) complexes, these Mn(I)-NHC complexes 1 and 2 were tested for the hydrosilylation of terminal alkynes. Complex 1 was proved to be an effective catalyst for the hydrosilylation of terminal alkynes with good selectivity toward the less thermodynamically stable ß-(Z)-vinylsilanes. This method provided good regioselectivity (anti-Markovnikov addition) and stereoselectivity (ß-(Z)-product). Experimental evidence suggested that the present hydrosilylation pathway involved an organometallic mechanism with manganese(I)-silyl species as a possible reactive intermediate.

Copper(i)-catalyzed click chemistry in deep eutectic solvent for the syntheses of ß-d-glucopyranosyltriazoles.

In the last two decades, click chemistry has progressed as a powerful tool in joining two different molecular units to generate fascinating structures with a widespread application in various branch of sciences. copper(i)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction, also known as click chemistry, has been extensively utilized as a versatile strategy for the rapid and selective formation of 1,4-disubstituted 1,2,3-triazoles. The successful use of CuAAC reaction for the preparation of biologically active triazole-attached carbohydrate-containing molecular architectures is an emerging area of glycoscience. In this regard, a well-defined copper(i)-iodide complex (1) with a tridentate NNO ligand (L1) was synthesized and effectively utilized as an active catalyst. Instead of using potentially hazardous reaction media such as DCM or toluene, the use of deep eutectic solvent (DES), an emerging class of green solvent, is advantageous for the syntheses of triazole-glycohybrids. The present work shows, for the first time, the successful use of DES as a reaction medium to click various glycosides and terminal alkynes in the presence of sodium azide. Various 1,4-disubstituted 1,2,3-glucopyranosyltriazoles were synthesized and the pure products were isolated by using a very simple work-up process (filtration). The reaction media was recovered and recycled in five consecutive runs. The presented catalytic protocol generated very minimum waste as reflected by a low E-factor (2.21-3.12). Finally, the optimized reaction conditions were evaluated with the CHEM21 green metrics toolkit.

Azide-Alkyne Cycloaddition Catalyzed by Copper(I) Coordination Polymers in PPM Levels Using Deep Eutectic Solvents as Reusable Reaction Media: A Waste-Minimized Sustainable Approach.

Two air-stable copper(I)-halide coordination polymers 1 and 2 with NNS and NNO ligand frameworks were synthesized and successfully utilized as efficient catalysts in an important organic reaction, namely, copper-catalyzed azide-alkyne cycloaddition, which is generally conducted in a mixture of water and organic solvents. The azide-alkyne "click" reaction was successfully conducted in pure water at r.t. under aerobic conditions. Other green solvents, including ethanol and glycerol, were also effectively used. Finally, deep eutectic solvents as green and sustainable reaction media were successfully utilized. In deep eutectic solvents, complete conversion with excellent isolated yield was achieved in a short period of time (1 h) with low catalyst loading (1 mol %) at r.t. Full conversion could also be achieved within 24 h with ppm-level (50 ppm) catalyst loading at 70 °C. Optimized reaction conditions were used for the syntheses of a large number of 1,4-disubstituted 1,2,3-triazoles with various functionalities. Triazole products were easily isolated by simple filtration. The reaction media, such as water and deep eutectic solvents, were recovered and recycled in three consecutive runs. The limited waste production is reflected in a very low E-factor (0.3-2.8). Finally, the CHEM21 green metrics toolkit was employed to evaluate the sustainability credentials of different optimized protocols in various green solvents such as water, ethanol, glycerol, and deep eutectic solvents.

Efficient α-Alkylation of Arylacetonitriles with Secondary Alcohols Catalyzed by a Phosphine-Free Air-Stable Iridium(III) Complex.

A well-defined and readily available air-stable dimeric iridium(III) complex catalyzed α-alkylation of arylacetonitriles using secondary alcohols with the liberation of water as the only byproduct is reported. The α-alkylations were efficiently performed at 120 °C under solvent-free conditions with very low (0.1-0.01 mol %) catalyst loading. Various secondary alcohols including cyclic and acyclic alcohols and a wide variety of arylacetonitriles bearing different functional groups were converted into the corresponding α-alkylated products in good yields. Mechanistic study revealed that the reaction proceeds via alcohol activation by metal-ligand cooperation with the formation of reactive iridium-hydride species.