Development of Titania-supported Iridium Catalysts for the Acceptor-less Dehydrogenative Synthesis of Benzoxazoles

Abstract

Iridium catalysts supported on anatase with high surface area showed excellent activities for the acceptor-less dehydrogenation synthesis of benzoxazoles from 2-aminophenol and primary alcohols. The catalytic activity greatly depended on the titania supports, iridium precursors, and loading of iridium species. Catalysts supported on anatase JRC (Japan Reference Catalyst)-TIO-10 showed the highest activity for the dehydrogenative reaction. Preparation of catalysts using [Ir(cod)Cl]2 (cod 1,5-cyclooctadiene) as an iridium precursor resulted in higher activity than using Ir(acac)3 (acac acetylacetonate). Various primary alcohols were reacted to give corresponding benzoxazoles in high to moderate yields. The catalyst could be recycled without significant loss of activity, and no leaching of iridium species occurred into the solution. The hot filtration test strongly suggested that the catalysis occurs on the catalyst surface. Highly dispersed iridium species of less than 2 nm in diameter, which could be reduced at low temperature, were responsible for the excellent activity.

IrCo Nanoparticles Encapsulated with Carbon Nanotubes for Efficient and Stable Acidic Water Splitting

“…It has been noted in prior research that rapid heating is advantageous for the growth of CNTs. , In the rapid heating process, Ir-etch-ZIF-L-Co will be reconstituted to form IrCo NPs that can catalyze the volatile carbonaceous components of the decomposed ZIF structure and DCDA molecules as the carbon source to grow abundant CNTs encapsulated with IrCo NPs on CC (IrCo@CNT/CC). In addition, the pyrolysis process can cause the thermal condensation from DCDA to melamine, tris- s -triazine, and C 3 N 4 (210–660 °C) to release NH 3 gas, and the thorough decomposition of C 3 N 4 (660–740 °C) to release (CN) 2 and N 2 gas. , During the rapid heating process of the co-pyrolysis of Ir-etched ZIF-L-Co and DCDA, Ir and Co atoms can be reduced by NH 3 gas to form IrCo alloyed NPs, which further catalyze the volatilized carbonaceous components from ZIF decomposition and (CN) 2 to grow CNTs . For comparison, three other electrocatalysts, namely porous carbon nanosheets encapsulated with IrCo alloyed NPs on CC (denoted as IrCo@PC/CC), CNTs encapsulated with Co NPs on CC (denoted as Co@CNT/CC), and porous carbon nanosheets encapsulated with Co NPs on CC (denoted as Co@PC/CC) were also prepared, and their synthesis procedures are schematically illustrated in Figure S5 (see details in the Supporting Information).…”

Advances in the synthetic strategies of benzoxazoles using 2-aminophenol as a precursor: an up-to-date review

“…Han and co-workers 78 developed a titania-supported iridium catalyst by an impregnation method and used it to prepare 2-substituted benzoxazoles ( 9 ) via acceptor-less dehydrogenative synthesis using 2-aminophenol ( 1 ) and primary alcohols ( 15 ) in mesitylene under an argon atmosphere at 80–170 °C for 18 h to give decent yields. This protocol has special properties like an easily recoverable and reusable catalyst with high efficiency, broad substrate scope, high yield, and low waste generation.…”