Oppenauer-type Oxidation Of Secondary Alcohols Research Articles

Phosphine-free ruthenium complexes supported by a pincer ligand bearing 1,2-dihydropyrimidine for Oppenauer-type oxidation of secondary alcohols

Treatment of the (diethylaminomethyl-picolyl)pyrazolium (A3) with NaOH in dichloromethane affords the pincer ligand (L) bearing a 1,2-dihydropyrimidine unit. Reaction of [RuCl2(DMSO)4] and the ligand (L) affords the complex [RuCl2(L)(DMSO)] (Ru1). Removal of the chlorides from Ru1 with either NaBF4 or KPF6 in CH3CN produces the complexes [Ru(L)(CH3CN)3](BF4)2 (Ru2) and [Ru(L)(CH3CN)3](PF6)2 (Ru3), respectively. Ru2 has been characterized with X-ray crystallography. All of the new ruthenium complexes (Ru1-Ru3) are catalytically active in the Oppenauer-type oxidation of secondary alcohols. Among them, the complex Ru1 is the most active. Steric effects were observed from the outcome of substituted acetophenones.

ChemInform Abstract: Aqueous‐Phase Catalytic Oxidation, Transfer Hydrogenation, Reductive Amination and Hydration Reactions

AbstractReview: 72 refs.

ChemInform Abstract: Ruthenium(II)—NNN Complex Catalyzed Oppenauer‐Type Oxidation of Secondary Alcohols.

Highly efficient Oppenauer-type oxidation of secondary alcohols to the corresponding ketones has been realized by means of the ruthenium(II) complex catalysts bearing a 2-(benzoimidazol-2-yl)-6-(3,5-dimethylpyrazol-1-yl)pyridine ligand. The oxidation reaction underwent in the presence of acetone as oxidant under mild conditions, reaching final TOF values up to 3960 h(-1). The hemilability of the ligand is attributed to the high catalytic activity of these Ru(II) complexes. (c) 2014 Elsevier Ltd. All rights reserved.

Aqueous-phase catalytic oxidation, transfer hydrogenation, reductive amination and hydration reactions

As part of our work devoted to the synthesis of organic compounds using “green” processes, we developed several water-soluble catalysts that allow efficiently the synthesis of ketones, amines, alcohols and amides. CuCl2·2H2O combined to 2,2′-biquinoline-4,4′-dicarboxylic acid dipotassium salt (BQC) was reported as an active catalyst for the selective oxidation with TBHP of alcohols, alkylarenes and alkynes. We developed also successfully hydrogen transfer reactions. While [Ir(COD)Cl]2/BQC proved to be efficient for Oppenauer-type oxidation of secondary alcohols, [Rh(COD)Cl]2/P(m-C6H4SO3Na)3 (TPPTS) showed very good activities for Meerwein–Ponndorf–Verley-type reduction of ketones and aldehydes. Higher alkylated amines and amides were also synthesized respectively, by direct reductive amination of aldehydes with primary and secondary amines catalyzed by water soluble Pd(PhCN)2Cl2/BQC, and hydration of nitriles with [Rh(COD)Cl]2/TPPTS. Many of these catalytic systems are recycled with no significant loss of activity and the final products are isolated in easy manners.

Ruthenium(II)–NNN complex catalyzed Oppenauer-type oxidation of secondary alcohols

Highly efficient Oppenauer-type oxidation of secondary alcohols to the corresponding ketones has been realized by means of the ruthenium(II) complex catalysts bearing a 2-(benzoimidazol-2-yl)-6-(3,5-dimethylpyrazol-1-yl)pyridine ligand. The oxidation reaction underwent in the presence of acetone as oxidant under mild conditions, reaching final TOF values up to 3960h−1. The hemilability of the ligand is attributed to the high catalytic activity of these Ru(II) complexes.

Oppenauer-type oxidation of secondary alcohols catalyzed by homogeneous water-soluble complexes

The catalytic system composed of [Ir(COD)Cl]2, 2,2′-biquinoline-4,4′-dicarboxylic acid dipotassium salt (BQC), and sodium carbonate is highly efficient for the selective oxidation of benzylic, 1-heteroaromatic, aliphatic, and allylic secondary alcohols using catalyst:substrate ratios ranging from 0.4% to 2.5%. Sterically hindered allylic alcohols undergo selectively good conversions to the corresponding enones, while unhindered ones are completely isomerized to saturated ketones. Mercury tests indicate that the catalytic process is likely homogeneous. The mechanism proposed for this Oppenauer-type oxidation including the isomerization process is based on iridium-alkoxide species.Key words: Oppenauer oxidation, water, catalysis, isomerization, secondary alcohols.

First example of water-soluble transition-metal catalysts for Oppenauer-type oxidation of secondary alcohols

The first water-soluble transition-metal catalysts for Oppenauer-type oxidation of secondary alcohols have been developed. The catalytic system composed of [Ir(COD)Cl]2, 2,2′-biquinoline-4,4′-dicarboxylic acid dipotassium salt (BQC) and sodium carbonate is highly efficient for the selective oxidation of benzylic and aliphatic secondary alcohols to the corresponding ketones with catalyst/substrate ratios ranging from 0.4 to 2.5%. The substitution of [Ir(COD)Cl]2 by its rhodium analog [Rh(COD)Cl]2 generates a less active catalytic system. [Ir(COD)Cl]2/BQC was also found to be more active than its water-insoluble analog system [Ir(COD)Cl]2/2,2′-biquinoline (BC).