Mechanism of Pd(OAc)₂/DMSO-Catalyzed Aerobic Alcohol Oxidation:  Mass-Transfer-Limitation Effects and Catalyst Decomposition Pathways

Abstract

Pd(OAc)(2) in DMSO is an effective catalyst for the aerobic oxidation of alcohols and numerous other organic substrates. Kinetic studies of the catalytic oxidation of primary and secondary benzylic alcohol substrates provide fundamental insights into the catalytic mechanism. In contrast to the conclusion reached in our earlier study (J. Am. Chem. Soc. 2002, 124, 766-767), we find that Pd(II)-mediated alcohol oxidation is the turnover-limiting step of the catalytic reaction. At elevated catalyst loading, however, the rate of catalytic turnover is limited by the dissolution of oxygen gas into solution. This mass-transfer rate is measured directly by using gas-uptake methods, and it correlates with the maximum rate observed during catalysis. Initial-rate studies were complemented by kinetic analysis of the full-reaction timecourses at different catalyst concentrations. Kinetic fits of these traces reveal the presence of unimolecular and bimolecular catalyst decomposition pathways that compete with productive catalytic turnover.

Singlet oxygen reactivity in water-rich solvent mixtures

“…The molecular oxygen concentration in the different solvent mixtures was determined assuming a linear additivity of the molecular oxygen solubilities, in dioxane (7.55 mM) and in water (1.325 mM), for oxygen saturated solutions. 18,19 Water molar concentration ranged from 28 M (50% v/v) to 50 M (90% v/v) in the solvent mixtures were used in this work. 2 show ground state absorption and fluorescence spectra of 3MI substrate and PSO photosensitizer, in H 2 O/Dx mixture (with 90% v/v water).…”

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.…”

Palladium‐Catalyzed Oxidative Cyclization of Enynes with Hydrogen Peroxide as the Oxidant

“…[8] In many cases, palladium catalyzes the rapid disproportionation of hydrogen peroxide. [9] Herein, we report an efficient palladium-catalyzed oxidative cyclization of enynes in which H 2 O 2 is used as the stoichiometric oxidant at room temperature. These reactions appear to proceed through a mechanism involving the oxidation of C(sp 3 ) À Pd II species by H 2 O 2 , and the formation of C À Cl bonds by a direct reductive elimination pathway that leads to the retention of the configuration at the carbon center.…”