Catalytic Base‐Free Transfer Hydrogenation of Biomass Derived Furanic Aldehydes with Bioalcohols and PNP Pincer Complexes

Abstract

The base‐free transfer hydrogenation of biomass derived furanic aldehydes with ruthenium and iridium pincer complexes was studied using bio‐alcohols as the hydrogen source. The furanic substrates, such as 5‐hydroxymethyl furfural (HMF) and thiophene‐2‐carboxaldehyde (TC), were reduced under mild conditions (35–80 °C) affording the desired alcohols with excellent conversions and yields. It was also possible to extend this methodology for the transfer hydrogenation of 5‐formylfurfural (DFF) at 130 °C. Deuterium labelling of C−H functions in the furanic alcohols was also investigated in the presence of ethanol‐d6. Finally, proposed catalytic resting species derived from the interactions between one of the catalysts and furanic reagents/product as well as the solvent during the transfer hydrogenation (TH) reaction were analysed.

Base-Free Transfer Hydrogenation Catalyzed by Ruthenium Hydride Complexes of Coumarin-Amide Ligands

“…Both complexes d and e catalyzed the TH of acetophenone in i PrOH at 82 °C (i.e., reflux temperature) and thus acquired red flags for energy. , Although complex f catalyzed the TH of acetophenone in i PrOH at 40 °C but the conversion was only 45.4% in 4 h, thus, resulted in a red flag for the lower product yield . The TH of 5-hydroxymethylfurfural by complex g as a catalyst acquired a red flag for the use of elevated temperature of 130 °C . Complex h catalyzed the TH of acetophenone in i PrOH at 85 °C while yielding 87% product.…”

“…36 The TH of 5-hydroxymethylfurfural by complex g as a catalyst acquired a red flag for the use of elevated temperature of 130 °C. 37 Complex h catalyzed the TH of acetophenone in i PrOH at 85 °C while yielding 87% product. This method received an amber flag for yield and a red flag under the energy category.…”

“…Similarly, complex f of a Schiff base-based ligand acted as an efficient catalyst for the TH of ketones . A Ru-dihydride complex g of a NP 2 -ligand has been employed for the TH of biomass derived furanic aldehydes . Commercially available complex h is also known as a successful catalyst for the TH of ketones and aldehydes .…”

“…36 A Ru-dihydride complex g of a NP 2 -ligand has been employed for the TH of biomass derived furanic aldehydes. 37 Commercially available complex h is also known as a successful catalyst for the TH of ketones and aldehydes. 38 It is important to note that both complexes b and e required a base for a better catalytic performance.…”

Direct valorization of biomass waste to gamma-valerolactone

“…Notably, there exist relatively few examples of homogeneous catalytic hydrogenations under acidic conditions [18][19][20][21][22][23][24] . Furthermore, the Noyori-type PNP pincer complexes 25 , such as the Ru-MACHO complex 26 and analogs, have demonstrated excellent activity in both basic [27][28][29] and neutral media [30][31][32][33] , but to the best of our knowledge, never under Brønsted acid conditions.…”