Rhenium-Catalyzed Dehydration and Deoxydehydration of Alcohols and Polyols: Opportunities for the Formation of Olefins from Biomass

Abstract

In view of the depletion of petroleum oils, new synthetic routes for the sustainable production of chemicals, fuels, and energy from renewable biomass sources are currently widely investigated. In particular, nonedible sugars and polyols are promising starting materials to produce olefins by dehydration, deoxygenation, or deoxydehydration (DODH) of these poly vicinal alcohols. In this perspective, we highlight the recent evolution of rhenium-catalyzed dehydration and DODH of biomass-derived alcohols and polyols to obtain olefins. Improving over the classical acid-catalyzed dehydration reaction, rheniummediated systems are very selective and more active to provide high yields of olefin products, but dehydration alone cannot be used to fully defunctionalize sugars. This issue is addressed by a growing research effort in the field of Re-catalyzed DODH, which allows complete dehydroxylation to form olefins in high yield. Recent developments in this field include the development of new molecular rhenium catalysts, the application of cheaper and more available reductants, and a growing mechanistic understanding owing to both experimental and computational studies. Finally, recent efforts to move beyond rhenium toward cheaper metals (Mo, V) are discussed.

Homogeneous Catalyzed Reactions of Levulinic Acid: To γ‐Valerolactone and Beyond

“…The in situ generated catalyst with monodentate P n Oct 3 and Ru(acac) 3 in the presence of NH 4 PF 6 gave GVL in 99% yield at 160 o C and 100 bar H 2 in neat LA. Applying the same reaction conditions using the bidentate DPPB and tridentate ligand triphos ligands gave yields of 89% and 8% of GVL respectively.…”

“…[28][29][30][31] In early pioneering studies Osakada et al, [32] showed the activation of C-O bonds of five membered cyclic anhydride, aldehydic and keto acids using two different ruthenium ( [10] demonstrated the use of an in situ generated Ru catalyst using a combination of Ru(acac) 3 and the strongly electron donating phosphine P n Bu 3 in the presence of NH 4 PF 6 for LA hydrogenation to GVL ( [33] reported the effect of the mondentate and chelating phosphines: trioctylphosphine (P n Oct 3 ), 1,4-diphenylphosphinobutane (DPPB) and triphos ( fig. 2) and various acidic additives for the transformation of LA.…”

“…Beller and coworkers [35] recently screened a wide range of bidentate and tridentate phosphine ligands for methyl levulinate (MLA) to GVL conversions. Catalysts were generated in situ using Ru(acac) 3 Iridium half-sandwich bipyridyl complexes ( fig. 4) have also been used to convert LA into GVL in high yields and under mild temperatures of 120 o C and pressures of 10 bar H 2 , and with some of the highest TON (78,000) reported to date.…”

“…Horváth and co-workers were one of the first to employ the water soluble sulfonated triphenylphosphine ligand TPPTS ( fig. 2) with Ru(acac) 3 for LA to GVL conversions under pressures of 69 bar H 2 and 140 o C (table 1, entry 4). [10] GVL was extracted from the aqueous phase with ethyl acetate giving high isolated yields of 95%.…”

“…[1,2] Plant biomass is the most abundant and available source of biorenewable carbon on our planet, and is viewed as the main sustainable alternative to petrochemical derived chemicals and fuels. [1,3,4] Lignocellulosic plant material in particular has been specifically earmarked for conversion to higher value chemicals and fuels. The vast natural abundance of lignocellulosic material and potential for further functionalisation to generate industrially important chemicals could make them viable alternatives to crude oil derived products.…”