Hydrogen production from ethanol catalysed by Group 8 metal complexes

On the Importance of Decarbonylation as a Side‐Reaction in the Ruthenium‐Catalysed Dehydrogenation of Alcohols: A Combined Experimental and Density Functional Study

“…[8] As 22 can be readily prepared under similar conditions (in methanol or ethanol, in presence of base and under a flux of hydrogen gas), [9] there should be a significant driving force for its formation under catalytic conditions, at the expense of dehydrogenation. Support for this scenario comes from the observation of higher TOFs for dehydrogenation under irradiation conditions, [5] which is expected to induce photodissociation of the coordinated CO ligands and regenerate the active catalyst 1. A comprehensive picture of this catalytic system at the molecular level would therefore require the understanding of all these individual reactions, and detailed insights into the ways how they are (inter)connected.…”

“…As a result, the reasons why one system is more active than another still remain difficult to rationalize, and the development of new, more active, systems is tied to the success of a rather empirical "trial-and-error" approach. Morton and Cole-Hamilton's system [5] represents a prototypical example of how complicated such catalytic systems can be. While it does produce the desired hydrogen, there are also a number of side reactions that limit its practical use.…”

“…[4] Hydrogen can be released via transitionmetal catalyzed dehydrogenation of the substrates and the first very active system was developed by Morton and Cole-Hamilton, showing that high turnover frequencies (TOFs) for production of H 2 can be obtained at 150 °C, using the [RuH 2 (X)(PPh 3 ) 3 ] catalyst (where X = N 2 , PPh 3 or H 2 ) in the presence of a base. [5] Several alcohol substrates have been screened, showing that methanol is only poorly converted whereas higher alcohols are more reactive. Subsequent studies report even higher activities at milder temperature, obtained by modifying the nature of the ligands and of the base.…”

“…Not only can the produced aldehydes undergo aldol and Tischenko reactions under the reaction conditions, they can also react with the Ru catalyst in a decarbonylation reaction generating carbonyl complexes such as [RuH 2 (CO)(PPh 3 ) 3 ] (22, see Scheme 1). 22 is also active as a dehydrogenation catalyst, [5,7] adding to the complexity of the system. [8] As 22 can be readily prepared under similar conditions (in methanol or ethanol, in presence of base and under a flux of hydrogen gas), [9] there should be a significant driving force for its formation under catalytic conditions, at the expense of dehydrogenation.…”

Lactic acid and hydrogen from glycerol via acceptorless dehydrogenation using homogeneous catalysts

“…pyrrolidine to pyrrole), which led to a new concept of ´´organic liquids´´ as hydrogen storage materials (HSMs) [10]. Also the dehydrogenation of alcohols has received particular attention recently, primarily due to implications in the conversion of renewables, although the first examples date back to a few decades ago [11][12][13][14][15]. This simple reaction is used in a wide range of chemical transformations, providing access to a variety of different products that are schematically illustrated in scheme 2.…”