Selectivity Control in Photocatalytic Transfer Hydrogenation of Bio‐based Aldehydes

Abstract

The development of selectivity control strategies based on external operational conditions without modification of catalyst is an attractive but challenging issue in photocatalysis. Herein we reported the substrate concentration-switched selectivity in photocatalytic transfer hydrogenation of biomass-derived aromatic aldehydes. With the same catalyst, hydrodeoxygenation was realized at low aldehyde concentration and reductive etherification was realized at high aldehyde concentration. Mechanistic studies revealed that the substrate concentration affected the electron density on catalyst, thus controlled the initial reduction of formyl group and types of intermediates. Competitive adsorption of these intermediates on the catalyst affected hydrogenolysis of CÀ O bonds in the later stage. This method is easy to handle, and achieved selective hydrogenation of diverse bio-based aldehydes to corresponding deoxygenated products and unsymmetric ether products as potential fuel additives under mild conditions. This work sheds light on the effect of substrate concentration on the selectivity in photocatalysis.

Heterogeneous photocatalytic valorization of lignocellulose biomass for chemical and fuel production via reductive pathways

“…The product distribution was influenced by reactant concentration modulation. 127 Lower concentration (0.01 mmol) favored MMP production (81%), while higher concentration (0.1 mmol) favored ether formation (76%) without phenolic group esterification (Table 2, entries 25 and 26). Under light, ethanol oxidation generated alkoxy radicals and protons.…”

Photocatalytic transfer hydrogenolysis of aryl ethers

“…Then, the DPE substrate can be reductively cleaved by the metal-hydrogen species. 56,57 However, the hydrogenation of the aryl ring and hydrogenolysis of the C-O bond may occur simultaneously (Fig. 1b).…”

“…In the past decade, the emerging photocatalytic technology has become a powerful tool for the conversion of biomass and its platform molecules into useful products under mild conditions. [50][51][52][53][54][55][56][57] Photocatalytic transfer hydrogenolysis was first developed for the cleavage of the β-O-4 linkage. The hydrogen atom at benzylic alcohol was readily abstracted and transferred to cleave the aliphatic ether bond.…”

Metal-Loaded Semiconductor-Photocatalysis of Alcohols for Selective Organic Synthesis: A Personal Account

“…Other researchers reported similar systems using Pd/SPs for dehydroxylative hydrogenolysis of benzylic alcohols, where the transformation of allylic alcohols was not tested. [31][32][33] 3.…”

“…similar systems using Pd/SPs for dehydroxylative hydrogenolysis of benzylic alcohols, where the transformation of allylic alcohols was not tested. [31][32][33] 3 Acceptorless Dehydrogenation of Activated/Unactivated Alcohols…”