“…The molecular structures exhibit typical three-legged 'piano-stool' configurations, similar to other known Cp-based rhenium compounds ( Figure 1). The OCÀReÀCO angles in 1 are between 89.18(9) and 90.84(7)8, the CÀC (Cp) distances are in the range 1.420(2)-1.472 (2) , and the Re to Cp (centroid) distance is 1.9569(7) . The CÀC(Cp) distances in 2 are in the range 1.408(3)-1.450(2) .…”
Section: Resultsmentioning
confidence: 99%
“…In particular, this approach will yield olefins, which are essential chemicals for both the polymer and the bulk chemical industries. [2] The production of olefins from sugars and sugar-derived polyols is viable through deoxygenation [3] and dehydration, [4,5] or combinations of these reactions, such as di-dehydroxylation [6] or deoxydehydration reactions. [7][8][9][10][11][12] Although alcohol dehydrations are well-known acid-catalysed and high-temperature transformations, [13] transition-metal-catalysed versions of these reactions have been studied to a lesser extent.…”
A bulky cyclopentadienyl (Cp)-based trioxorhenium compound was developed for the catalytic deoxydehydration of vicinal diols to olefins. The 1,2,4-tri(tert-butyl)cyclopentadienyl trioxorhenium (2) catalyst was synthesised in a two-step synthesis procedure. Dirhenium decacarbonyl was converted into 1,2,4-tri(tert-butyl)cyclopentadienyl tricarbonyl rhenium, followed by a biphasic oxidation with H2 O2 . These two new three-legged compounds with a 'piano-stool' configuration were fully characterised, including their single crystal X-ray structures. Deoxydehydration reaction conditions were optimised by using 2 mol % loading of 2 for the conversion of 1,2-octanediol into 1-octene. Different phosphine-based and other, more conventional, reductants were tested in combination with 2. Under optimised conditions, a variety of vicinal diols (aromatic and aliphatic, internal and terminal) were converted into olefins in good to excellent yields, and with minimal olefin isomerisation. A high turnover number of 1400 per Re was achieved for the deoxydehydration of 1,2-octanediol. Furthermore, the biomass-derived polyols (glycerol and erythritol) were converted into their corresponding olefinic products by 2 as the catalyst.
“…The molecular structures exhibit typical three-legged 'piano-stool' configurations, similar to other known Cp-based rhenium compounds ( Figure 1). The OCÀReÀCO angles in 1 are between 89.18(9) and 90.84(7)8, the CÀC (Cp) distances are in the range 1.420(2)-1.472 (2) , and the Re to Cp (centroid) distance is 1.9569(7) . The CÀC(Cp) distances in 2 are in the range 1.408(3)-1.450(2) .…”
Section: Resultsmentioning
confidence: 99%
“…In particular, this approach will yield olefins, which are essential chemicals for both the polymer and the bulk chemical industries. [2] The production of olefins from sugars and sugar-derived polyols is viable through deoxygenation [3] and dehydration, [4,5] or combinations of these reactions, such as di-dehydroxylation [6] or deoxydehydration reactions. [7][8][9][10][11][12] Although alcohol dehydrations are well-known acid-catalysed and high-temperature transformations, [13] transition-metal-catalysed versions of these reactions have been studied to a lesser extent.…”
A bulky cyclopentadienyl (Cp)-based trioxorhenium compound was developed for the catalytic deoxydehydration of vicinal diols to olefins. The 1,2,4-tri(tert-butyl)cyclopentadienyl trioxorhenium (2) catalyst was synthesised in a two-step synthesis procedure. Dirhenium decacarbonyl was converted into 1,2,4-tri(tert-butyl)cyclopentadienyl tricarbonyl rhenium, followed by a biphasic oxidation with H2 O2 . These two new three-legged compounds with a 'piano-stool' configuration were fully characterised, including their single crystal X-ray structures. Deoxydehydration reaction conditions were optimised by using 2 mol % loading of 2 for the conversion of 1,2-octanediol into 1-octene. Different phosphine-based and other, more conventional, reductants were tested in combination with 2. Under optimised conditions, a variety of vicinal diols (aromatic and aliphatic, internal and terminal) were converted into olefins in good to excellent yields, and with minimal olefin isomerisation. A high turnover number of 1400 per Re was achieved for the deoxydehydration of 1,2-octanediol. Furthermore, the biomass-derived polyols (glycerol and erythritol) were converted into their corresponding olefinic products by 2 as the catalyst.
“…There is intense interest in finding ways to use transition-metal complexes to activate strong bonds in simple diatomic and triatomic molecules, with applications in areas such as artificial nitrogen fixation and carbon dioxide utilization . While rhenium oxo compounds have found applications in organic synthesis , and in biomass conversion, their role in transforming simple diatomic and triatomic molecules has been largely neglected. This is surprising because rhenium can support a number of oxidation states, allowing rhenium oxo compounds to behave as either oxygen atom donors or acceptors and thus, oxidize or reduce substrates.…”
The rhenium dioxide anion [ReO2](-) reacts with carbon dioxide in a linear ion trap mass spectrometer to produce [ReO3](-) corresponding to activation and cleavage of a C-O bond. Isotope labeling experiments using [Re(18)O2](-) reveal that (18)O/(16)O scrambling does not occur prior to cleavage of the C-O bond. Density functional theory calculations were performed to examine the mechanism for this oxygen atom abstraction reaction. Because the spins of the ground states are different for the reactant and product ions ((3)[ReO2](-) versus (1)[ReO3](-)), both reaction surfaces were examined in detail and multiple [O2Re-CO2](-) intermediates and transition structures were located and minimum energy crossing points were calculated. The computational results show that the intermediate [O2Re(η(2)-C,O-CO2)](-) species most likely initiates C-O bond activation and cleavage. The stronger binding affinity of CO2 within this species and the greater instabilities of other [O2Re-CO2)](-) intermediates are significant enough that oxygen atom exchange is avoided.
“…1b) that selectively hydrogenate and/or functionalize a wide range of functionalized CAs. The majority of high-valent Re complexes have thus far been used for oxidation 31 and deoxydehydration 31, 32 , rather than for FGT of CA (α-C–H functionalization 15 and hydrogenation 23, 33 ).Figure 1Overview of the present work ( a ). Overcoming the drawbacks of previously reported catalytic systems for the chemoselective hydrogenation of CAs.…”
Carboxylic acids (CAs) are one of the most ubiquitous and important chemical feedstocks available from biorenewable resources, CO2, and the petrochemical industry. Unfortunately, chemoselective catalytic transformations of CHnCO2H (n = 1–3) groups into other functionalities remain a significant challenge. Herein, we report rheniumV complexes as extremely effective precatalysts for this purpose. Compared to previously reported heterogeneous and homogeneous catalysts derived from high- or low-valent metals, the present method involves a α-C–H bond functionalization, a hydrogenation, and a hydrogenolysis, which affords functionalized alcohols with a wide substrate scope and high chemoselectivity under relatively mild reaction conditions. The results represent an important step toward a paradigm shift from ‘low-valent’ to ‘high-valent’ metal complexes by exploring a new portfolio of selective functional group transformations of highly oxygenated organic substrates, as well as toward the exploitation of CAs as a valuable biorenewable feedstock.
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