Mechanistic study of C–H bond activation by O₂ on negatively charged Au clusters: α,β-dehydrogenation of 1-methyl-4-piperidone by supported Au catalysts

Abstract

Au nanoparticles supported on manganese oxide octahedral molecular sieve (OMS-2) can efficiently catalyze α,β-dehydrogenation of β-N-substituted saturated ketones using O2 as the terminal oxidant. However, despite the utility of this...

Supported Anionic Gold Nanoparticle Catalysts Modified Using Highly Negatively Charged Multivacant Polyoxometalates

“…With reference to general understandings that O 2 can be reductively activated on anionic Au surface, [12–17] four possible reaction pathways were proposed toward this catalysis based on our previous studies (Figures S14 and S15) [36, 37] . The activation of O 2 in the presence of anionic Au nanoparticles was found to be important in all possible reaction pathways, considerably facilitating the oxidative dehydrogenation of piperidone derivatives.…”

“…Toward synthesis of enaminones, versatile synthetic intermediates for various organic compounds including heterocyclic compounds and natural products, [46] we had developed an efficient aerobic oxidative dehydrogenation of piperidone derivatives using supported Au nanoparticle catalysts [36] . Our further theoretical calculation revealed that, like some other aerobic oxidation reactions, [11–17, 47, 48] efficient activation of O 2 on negatively‐charged Au surface led to an excellent activity [37] . Therefore, we focused on this catalysis as a model reaction in order to evaluate the as‐proven supported anionic Au nanoparticle catalysts.…”

C–H Bond Activation Mechanism by a Pd(II)–(μ-O)–Au(0) Structure Unique to Heterogeneous Catalysts

“…M06 is an exchange–correlation functional often used in systems with transition metals especially Au, 38 , 48 , 49 and SDD is a basis set often used in systems with Au or Pd. 38 , 50 , 51 The solvent effect was calculated with a conductor-like polarizable continuum model using toluene. The transition state structures contained one imaginary frequency exhibiting atom displacements along the expected reaction pathway.…”

“…Our previous work on the Au-catalyzed α,β-dehydrogenation of 1-methyl-4-piperidone was computationally expensive because our use of various Au cluster models forced us to consider many adsorption sites for O 2 to cleave C–H bonds. 38 Also, oversimplifying the model of supported nanoparticle catalysts may result in conclusions that are inconsistent with reality. To elucidate the mechanism and establish a design strategy for heterogeneous catalysts, an established active site structure-catalyzed important elementary reaction such as C–H bond activation needs to be considered based on multiple aspects combined with experimental and theoretical approaches.…”

“…This may be because experimentally determining the exact active site structures of supported catalysts is quite difficult, which forces calculations to consider various active site models as possibilities. Our previous work on the Au-catalyzed α,β-dehydrogenation of 1-methyl-4-piperidone was computationally expensive because our use of various Au cluster models forced us to consider many adsorption sites for O 2 to cleave C–H bonds . Also, oversimplifying the model of supported nanoparticle catalysts may result in conclusions that are inconsistent with reality.…”