Copper(I)/TEMPO-catalyzed aerobic oxidation of primary alcohols to aldehydes with ambient air

Abstract

This protocol describes a practical laboratory-scale method for aerobic oxidation of primary alcohols to aldehydes, using a chemoselective CuI/TEMPO catalyst system. The catalyst is prepared in situ from commercially available reagents, and the reactions are performed in a common organic solvent (acetonitrile) with ambient air as the oxidant. Three different reaction conditions and three procedures for the isolation and purification of the aldehyde product are presented. The oxidations of eight different alcohols, described here, include representative examples of each reaction condition and purification method. Reaction times vary from 20 min to 24 h, depending on the alcohol, while the purification methods each take about 2 h. The total time necessary for the complete protocol ranges from 3 – 26 h.

Catalytic oxidation of cyclohexane with hydrogen peroxide and a tetracopper(II) complex in an ionic liquid

“…PPh 3 reduces CyOOH to CyOH, resulting in an increase in the alcohol amount and a decrease in that of CyO. This behavior has been observed in several peroxidative oxidation systems [2(h),2(r),3(g), 11,12].…”

Chiral tetranuclear and dinuclear copper(ii) complexes for TEMPO-mediated aerobic oxidation of alcohols: are four metal centres better than two?

“…11 Recent progress indicates that both Cu(I) and Cu(II) complexes with a N,N-or N,O-ligands in combination with TEMPO could be efficient catalysts or catalyst precursors for the aerobic oxidation of various alcohols, and of particular note is a highly efficient copper/2,2'-bipyridine/TEMPO system developed by the Stahl group. [12][13][14][15][16][17] However, the types of organic ligands exploited in the copper catalyst systems are still limited and the structures of copper catalysts involved in the catalytic process are rarely explored. [17][18][19][20] The construction of metal-organic cluster compounds through self-assembly of predesigned ligands with appropriate metal ions is a prime research topic [21][22][23][24][25] due to the advantages in catalysing useful chemical transformations, in contrast to simple monometallic complexes.…”

Copper(II) complexes derived from bidentate N,O-ligands for catalytic aerobic oxidation

“…In 1984, Semmelhack and co-workers carried out a copper-catalyzed, 2,2,6,6-tetramethylpiperidinyl-1-oxyl(TEMPO)-mediated aerobic oxidation of primary alcohols by using a simple Cu I Cl/TEMPO system in DMF (N,N-dimethylformamide) [21], and thereafter, a variety of Cu/TEMPO methodologies has been extensively developed for the aerobic oxidation of a range of aromatic and aliphatic primary alcohols by the Sheldon, Koskinen and Stahl groups [18,19,[22][23][24][25][26]. Amongst some efficient copper-based catalyst systems reported so far, a N,Nbidentate ligand was often employed as a reactivity promoter, this includes 2,2′-bipyridine (bpy), 1,10-phenanthroline and 1,4-diazabicylo [2,2,2]octane with bpy remaining the most popular choice [23][24][25][26].Except for the N,N-type ligands that were extensively investigated, N,O-chelating ligands have also been found to be suitable ligand candidates for this reaction, although such examples were only little reported [27][28][29][30][31]. The Punniyamurthy group reported that a salen-type N,Oligand promoted efficient oxidation of primary alcohols to aldehydes under oxygen conditions [27].…”

“…In contrast to some precious metal catalysts such as Pd II , Ru II and Ir II that were developed in the past few years [12][13][14][15][16], earth-abundant and inexpensive Cu II has recently attracted more attention, owing to its great potential as precious metal surrogate for catalysis in large-scale industrial applications [17][18][19][20]. In 1984, Semmelhack and co-workers carried out a copper-catalyzed, 2,2,6,6-tetramethylpiperidinyl-1-oxyl(TEMPO)-mediated aerobic oxidation of primary alcohols by using a simple Cu I Cl/TEMPO system in DMF (N,N-dimethylformamide) [21], and thereafter, a variety of Cu/TEMPO methodologies has been extensively developed for the aerobic oxidation of a range of aromatic and aliphatic primary alcohols by the Sheldon, Koskinen and Stahl groups [18,19,[22][23][24][25][26]. Amongst some efficient copper-based catalyst systems reported so far, a N,Nbidentate ligand was often employed as a reactivity promoter, this includes 2,2′-bipyridine (bpy), 1,10-phenanthroline and 1,4-diazabicylo [2,2,2]octane with bpy remaining the most popular choice [23][24][25][26].…”

“…Both Cu II complexes have been examined for the catalytic aerobic oxidation of benzylic alcohol in the presence of a TEMPO radical, and the results are summarized in Table 1. Initially, to compare the catalytic activity of new Cu II -N,O complexes 1 and 2 with the best performing Cu/bpy/TEMPO catalyst systems reported by Sheldon, Koskinen and Stahl's groups [21][22][23][24][25][26], the similar reaction conditions were employed. Thus, the reaction of benzylic alcohol (1 mmol) was first tested by using copper complex 1 as a catalyst (2 mol%) and 4-dimethylaminopyridine (DMAP) as a base at room temperature in acetonitrile with the presence of TEMPO (5 mol%).…”