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1. Selective C−O Bond Cleavage of Bio‐Based Organic Acids over Palladium Promoted MoO _x /TiO ₂

   https://doi.org/10.1002/cctc.202001799  

   Nacy, Ayad; de_Lima_e_Freitas, Lucas_Freitas; Albarracín‐Suazo, Sandra; Ruiz‐Valentín, Génesis; Roberts, Charles_A; Nikolla, Eranda; Pagán‐Torres, Yomaira_J (December 2020, ChemCatChem)

   Abstract Hydrodeoxygenation chemistries play a key role in the upgrading of biomass‐derived feedstocks. Among these, the removal of targeted hydroxyl groups through selective C−O bond cleavage from molecules containing multiple functionalities over heterogeneous catalysts has shown to be a challenge. Herein, we report a highly selective and stable heterogeneous catalyst for hydrodeoxygenation of tartaric acid to succinic acid. The catalyst consists of reduced Mo⁵⁺centers promoted by palladium, which facilitate selective C−O bond cleavage, while leaving intact carboxylic acid end groups. Stable catalytic performance over multiple cycles is demonstrated. This catalytic system opens up opportunities for selective processing of biomass‐derived sugar acids with a high degree of chemical functionality. 

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2. Highly efficient deoxydehydration and hydrodeoxygenation on MoS2-supported transition metal atoms through a C-H activation mechanism

   https://doi.org/10.1021/acscatal.0c02669  

   Xi, Yongjie; Heyden, Andreas (July 2020, ACS Catalysis)

   Deoxydehydration (DODH) is an efficient process for the removal of vicinal OH groups of a diol or polyol. Conventional DODH reactions usually take place at a single-site MOx (M=Re, Mo, V etc.) active center, which proceed through a diol condensation step, an alkene extrusion step and a catalyst regeneration (or reduction) step. Here, we suggest that MoS2-supported transition metal atoms allow for the DODH reaction to occur through an alternative mechanism, whereby the C-H bond of a diol is activated first, which facilitates the C-OH bond cleavage on a neighboring carbon. The removal of the second OH group is also facile over the proposed catalysts. Our kinetic studies suggest that the DODH of ethylene glycol on Ru2/MoS2, Ir2/MoS2 and Ru3/MoS2 are highly active with predicted turnover frequencies of over 1/s. Thus, our study suggests a possible approach for the design of highly active DODH catalysts. Apart from being a DODH catalyst, the proposed MoS2-supported catalysts are also highly active as hydrodeoxygenation catalyst for the removal of alcohol OH groups. 

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3. Photoelectrochemical approaches for the conversion of lignin at room temperature

   https://doi.org/10.1039/d2cc05491d  

   Li, Shuya; Park, Seongsu; Sherman, Benjamin D.; Yoo, Chang Geun; Leem, Gyu (January 2023, Chemical Communications)

   The selective cleavage of C–C/C–O linkages represents a key step toward achieving the chemical conversion of biomass to targeted value-added chemical products under ambient conditions. Using photoelectrosynthetic solar cells is a promising method to address the energy intensive depolymerization of lignin for the production of biofuels and valuable chemicals. This feature article gives an in-depth overview of recent progress using dye-sensitized photoelectrosynthetic solar cells (DSPECs) to initiate the cleavage of C–C/C–O bonds in lignin and related model compounds. This approach takes advantage of N -oxyl mediated catalysis in organic electrolytes and presents a promising direction for the sustainable production of chemicals currently derived from fossil fuels. 

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4. Highly Selective Oxygen Reduction to Hydrogen Peroxide on a Carbon-Supported Single-Atom Pd Electrocatalyst

   https://doi.org/10.1021/acscatal.1c05633  

   Wang, Nan; Zhao, Xunhua; Zhang, Rui; Yu, Saerom; Levell, Zachary H.; Wang, Chunyang; Ma, Shaobo; Zou, Peichao; Han, Lili; Qin, Jiayi; et al (March 2022, ACS Catalysis)

   Selective electrochemical two-electron oxygen reduction is a promising route for renewable and on-site H2O2 generation as an alternative to the anthraquinone process. Herein, we report a high-performance nitrogen-coordinated single-atom Pd electrocatalyst, which is derived from Pd-doped zeolitic imidazolate frameworks (ZIFs) through one-step thermolysis. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) combined with X-ray absorption spectroscopy verifies atomically dispersed Pd atoms on nitrogen-doped carbon (Pd-NC). The single-atom Pd-NC catalyst exhibits excellent electrocatalytic performance for two-electron oxygen reduction to H2O2, which shows ∼95% selectivity toward H2O2 and an unprecedented onset potential of ∼0.8 V versus revisable hydrogen electrode (RHE) in 0.1 M KOH. Density functional theory (DFT) calculations demonstrate that the Pd-N4 catalytic sites thermodynamically prefer *–O bond breaking to O–O bond breaking, corresponding to a high selectivity for H2O2 production. This work provides a deep insight into the understanding of the catalytic process and design of high-performance 2e– ORR catalysts. 

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5. Pd-Catalyzed Suzuki-Miyaura Cross-Coupling of Pentafluorophenyl Esters

   https://doi.org/10.3390/molecules23123134  

   Buchspies, Jonathan; J. Pyle, Daniel; He, Huixin; Szostak, Michal (December 2018, Molecules)

   Although the palladium-catalyzed Suzuki-Miyaura cross-coupling of aryl esters has received significant attention, there is a lack of methods that utilize cheap and readily accessible Pd-phosphane catalysts, and can be routinely carried out with high cross-coupling selectivity. Herein, we report the first general method for the cross-coupling of pentafluorophenyl esters (pentafluorophenyl = pfp) by selective C–O acyl cleavage. The reaction proceeds efficiently using Pd(0)/phosphane catalyst systems. The unique characteristics of pentafluorophenyl esters are reflected in the fully selective cross-coupling vs. phenolic esters. Of broad synthetic interest, this report establishes pentafluorophenyl esters as new, highly reactive, bench-stable, economical, ester-based, electrophilic acylative reagents via acyl-metal intermediates. Mechanistic studies strongly support a unified reactivity scale of acyl electrophiles by C(O)–X (X = N, O) activation. The reactivity of pfp esters can be correlated with barriers to isomerization around the C(acyl)–O bond. 

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