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

Abstract

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.

Nickel-Catalyzed α-Alkylation of Arylacetonitriles with Challenging Secondary Alcohols

“…5c,g We also used the approach in iridium-catalyzed α-alkylation of arylacetonitriles with secondary alcohols. 23 In this context, an imidazole-based ligand (L 1 ) with a pendant pyridine moiety was selected for the present work (Scheme 2). Although many groups reported various nickel catalysts for C−C 28 and C−N 29 bond forming reaction, there is no example of nickel catalyst for the α-alkylation of arylacetonitriles with secondary alcohols.…”

“…Based on the above control experiments, we propose a plausible catalytic path which is in line with previous reports (Scheme 4f). 19,20,22,23 Initially, the base reacts with precatalyst 1 and dehydrochlorination resulted in the formation of active catalyst elimination of water as the only byproduct. In the final step of the catalytic cycle, hydrogenation of vinyl nitrile takes place; hydrogen transfer from nickel-hydride species 3 to arylacrylonitrile results in the formation of the desired α-alkylated product and regenerates the active catalyst 2.…”

“…22 We published the latest report, and a dimeric iridium(III) complex was employed as a very effective catalyst. 23 Herein, we report the first example of nickel catalyst for the α-alkylation of arylacetonitriles with various secondary alcohols (Scheme 1).…”

“…1,128.8,128.0,127.9,120.4,44.8,44.5,33.2,30.6,27.8,27.7,26.2,acetonitrile (P 43 ). 23 The crude product was purified by column chromatography [silica as the stationary phase and a mixture of hexanes and ethyl acetate (9.8:0.2) as the eluent] to give pure product P 43 as a colorless oil (0.165 g, 73%). 1 H NMR (400 MHz, CDCl 3 ): δ 7.19−7.13 (m, 1H), 7.06− 6.99 (m, 3H), 3.60 (d, J = 6 Hz, 1H), 2.28 (s, 3H), 1.92−1.81 (m, 1H), 1.75−1.56 (m, 4H), 1.53−1.24 (m, 8H).…”

Base metal iron catalyzed sustainable oxidation of vanillyl alcohol to vanillic acid in deep eutectic solvents and implementation of vanillic acid for fine-chemical synthesis

“…Therefore, phosphine-free (and carbene-free) ligand synthesis is important for the development of air-stable complexes and gaining serious attention in homogeneous catalysis. [85][86][87][88][89] Particularly, air-sensitive metal complexes are of no use in the eld of oxidation of alcohols. Therefore, we wanted to use a tridentate NNN pincer ligand which is expected to give good stability of the resulting metal complex by tridentate coordination and might give an air-stable metal complex.…”