Gillesds

Synlett
DOI: 10.1055/s-0040-1720887

Self-assembled aggregates of 7,10-dibromo-2,3-dicyanopyrazinophenanthrene which act as a new organophotocatalyst in combination with Ni catalyst for the Caryl–Oacyl cross-coupling reactions of carboxylic acids with aryl halides are described. This visible-light-induced Caryl–Oacyl bond-formation reaction proceeds smoothly to afford aryl esters with satisfactory to excellent yields.
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Article in Thieme eJournals:
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Nature Catalysis, Published online: 21 September 2021; doi:10.1038/s41929-021-00674-2

A lignin to diesel precursors route was achieved via solar driven coupling reaction over Au/CdS photocatalyst. The diesel precursors can be further hydrogenated to C16–C18 cyclic hydrocarbons or aromatics over Pd/C or CoMoS-P, respectively.

Abstract

Producing renewable biofuels from biomass is a promising way to meet future energy demand. Here, we demonstrated a lignin to diesel route via dimerization of the lignin oil followed by hydrodeoxygenation. The lignin oil undergoes C−C bond dehydrogenative coupling over Au/CdS photocatalyst under visible light irradiation, co-generating diesel precursors and hydrogen. The Au nanoparticles loaded on CdS can effectively restrain the recombination of photogenerated electrons and holes, thus improving the efficiency of the dimerization reaction. About 2.4 mmol g_catal ⁻¹ h⁻¹ dimers and 1.6 mmol g_catal ⁻¹ h⁻¹ H₂ were generated over Au/CdS, which is about 12 and 6.5 times over CdS, respectively. The diesel precursors are finally converted into C16–C18 cycloalkanes or aromatics via hydrodeoxygenation reaction using Pd/C or porous CoMoS catalyst, respectively. The conversion of pine sawdust to diesel was performed to demonstrate the feasibility of the lignin-to-diesel route.

Methyl esters are shown to participate in intermolecular Suzuki–Miyaura cross-coupling reactions. Due to the mild nature of organoboron reagents, the product ketones are inert to the reaction conditions, avoiding over reactivity issues prominent with more aggressive organometallic nucleophiles.

Abstract

The direct conversion of alkyl esters to ketones has been hindered by the sluggish reactivity of the starting materials and the susceptibility of the product towards subsequent nucleophilic attack. We have now achieved a cross-coupling approach to this transformation using nickel, a bulky N-heterocyclic carbene ligand, and alkyl organoboron coupling partners. 65 alkyl ketones bearing diverse functional groups and heterocyclic scaffolds have been synthesized with this method. Catalyst-controlled chemoselectivity is observed for C(acyl)−O bond activation of multi-functional substrates bearing other bonds prone to cleavage by Ni, including aryl ether, aryl fluoride, and N-Ph amide functional groups. Density functional theory calculations provide mechanistic support for a Ni⁰/Ni^II catalytic cycle and demonstrate how stabilizing non-covalent interactions between the bulky catalyst and substrate are critical for the reaction's success.

Selective, active and stable heterogenous MoO_x−Pd/TiO₂ catalyst for hydrodeoxygenation of biomass‐derived feedstocks. High yields of 92 % succinic acid production from tartaric acid are reported over multiple catalytic cycles. This results from in‐situ reduction of supported MoO_x centers promoted by Pd on TiO₂.

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.