Cp*Ir Complexes Bearing N-Heterocyclic Carbene Ligands as Effective Catalysts for Oppenauer-Type Oxidation of Alcohols

Abstract

All reactions and manipulations were carried out under an atmosphere of argon by means of standard Schlenk techniques. 1 H and 13 C{ 1 H} NMR spectra were recorded on JEOL A-500 and EX-270 spectrometers. Gas chromatography analyses were performed on a Shimadzu GC-14A gas chromatograph with capillary column (Shimadzu CBP1-M25-025) or GL-Sciences GC353B gas chromatograph with capillary column (GL-Sciences TC-17). Melting points were determined on a Yanagimoto micro melting point apparatus. Elemental analyses were carried out at the

Electron-Rich CpIr(biphenyl-2,2′-diyl) Complexes with π-Accepting Carbon Donor Ligands

“…1–7 Several half-sandwich Ir III species catalyze water oxidation, 8–11 and our group has recently developed a wide variety of complexes of this type that are also active precatalysts for C–H bond oxidation. 12–16 These precatalysts give relatively high turnover frequencies for water oxidation in comparison to ruthenium-based systems, 17–25 but oxidative degradation of the molecular complexes is a concern.…”

Intramolecular Oxidation of the Alcohol Functionalities in Hydroxyalkyl‐N‐Heterocyclic Carbene Complexes of Iridium and Rhodium

“…Some Cp*Ir (Cp* = pentamethylcyclopentadienyl) complexes are known to be very active in the homogeneously catalyzed transformations of alcohols, [4] including their oxidation to aldehydes, [5,6] esterification, [7,8] b alkylation with primary alcohols [9,10] and coupling with amines, [10][11][12] among many other processes, most of them following the seminal works carried out by Fujita and Yamaguchi et al [5,12,13] We have also been interested in the application of Cp*Ir-A C H T U N G T R E N N U N G (NHC) complexes in catalytic reactions that involve the use of alcohols. [14] Because we are interested in experimentally studying the reaction mechanisms that involve the oxidation of alcohols by Ir III complexes, we thought that using N-heterocyclic carbenes with alcohol substituents at the NHC wingtips might shed some light into the reaction pathways that govern the processes.…”

Arylation of Carbonyl Compounds Catalyzed by Rhodium and Iridium 1,3‐R2‐Tetrahydropyrimidin‐2‐ylidenes: Structure‐Reactivity Correlations

“…[19 -25] Rh-NHC complexes have mainly been used in hydroformylation, [26] carbonyl hydrosilylation [27] and C ¼ C hydrosilylation. [21] Ir-NHC complexes were used in the Oppenauer-type oxidation of alcohols, [23] and as hydrogenation catalysts. [18] Miyaura et al were the first to report on the Rh(I)-catalyzed addition of aryl-and 1-alkenylboronic acids, respectively, to enones and aldehydes to yield the corresponding ketones and secondary alcohols, respective-ly.…”