Microwave-assisted pincer-ruthenium catalyzed Guerbet reaction for the upgradation of bio-ethanol to bio-butanol

Das, Kanu; Kathuria, Lakshay; Jasra, Raksh V.; Dhole, Sunil; Kumar, Akshai

doi:10.1039/d3cy00079f

Cited by 9 publications

(14 citation statements)

References 64 publications

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“…The NNN pincer–Ru acetonitrile complexes ( 3a–c ) were synthesized in good yields by the treatment of the corresponding ligands − with [Ru( p -cymene)Cl 2 ] 2 in acetonitrile under reflux conditions overnight, followed by washing with diethyl ether (Scheme ). The complexes 3a–c were fully characterized by high-resolution mass spectrometry (HRMS) and infrared (IR), 1 H, and 13 C nuclear magnetic resonance (NMR) studies.…”

Section: Results and Discussionmentioning

confidence: 99%

“…All catalytic reactions were set up under an argon atmosphere using dried glassware. The ligands 4a–c and complexes 1a–f and 2a–f were prepared according to the literature procedure. − , …”

Section: Methodsmentioning

confidence: 99%

“…The transition states were located using the synchronous transit-guided quasi-Newton (QST2) method. The method and basis set were selected on the basis of previous reports on pincer complexes . Frequency calculations were also done to differentiate minima structures or transition states on the potential energy surface.…”

Section: Methodsmentioning

confidence: 99%

“…The NNN pincer ligands employed in the current report are innocent, and the reactivity is expected to be metal-centered. Our group has previously reported a series of NNN pincer–ruthenium complexes ( 1a–f and 2a–f , Figure ) based on bis (imino)pyridine and 2,6- bis (benzimidazole-2-yl) pyridine ligands for catalytic reactions like N -alkylation, glycerol transformation to lactic acid, β-alkylation, and Guerbet reactions that involve dehydrogenation as a key step in the presence of varying amounts of base. Considering the fact that methanol reforming by homogeneous catalysts − also involves its dehydrogenation in the presence of typical bases as promoters, these NNN pincer–ruthenium complexes ( 1a–f and 2a–f , Figure ) are likely to be potential catalyst candidates for this valuable transformation.…”

Section: Introductionmentioning

confidence: 99%

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Pincer–Ruthenium-Catalyzed Reforming of Methanol─Selective High-Yield Production of Formic Acid and Hydrogen

et al. 2023

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A series of NNN pincer−ruthenium complexes of the type ( R2 NNN)RuCl 2 (CH 3 CN) based on bis(imino)pyridine ligands were synthesized and characterized. These pincer ruthenium acetonitrile complexes, along with their phosphine and carbonyl counterparts, were tested for the reforming of methanol in water in the presence of a base. The catalyst ( Cy2 NNN)-RuCl 2 (PPh 3 ) was found to be the most efficient in comparison to other considered catalysts. Among the bases screened, KO t Bu (1.5 equiv with respect to water) was found to give the best results at temperatures as low as 100 °C. Under these conditions, while ( Cy2 NNN)RuCl 2 (PPh 3 ) (0.2 mol %) in a mixture of methanol and water in a 2:1 ratio gave a yield of up to 81% each of hydrogen and formic acid (FA) at 100% selectivity, the corresponding reaction with 2 mol % ( Cy2 NNN)RuCl 2 (PPh 3 ) gave up to 90% of hydrogen and 73% of FA at 80% selectivity. On the other hand, the ( Cy2 NNN)RuCl 2 (PPh 3 ) (0.8 mol %) catalyzed reforming of a 3:1 methanol/water mixture gave good yields (84%) of hydrogen with 81% FA at 95% selectivity. The yield of hydrogen was cross-verified by using it to reduce unsaturated compounds and determining the corresponding yield of the reduced product, which was found to be consistent. Isotope-labeling studies suggest the involvement of C−H activation as a part of the catalytic cycle and not as a part of the rate-determining step (RDS) with an average secondary KIE of 1.96. The reaction was observed to have a first-order dependence of rate on the concentration of both ( Cy2 NNN)RuCl 2 (PPh 3 ) and methanol. DFT studies are in agreement with this, and the σ-bond metathesis leading to the elimination of the first molecule of hydrogen is computed to be the RDS either for the cycle leading to FA and 2 moles of hydrogen or for the cycle that results in carbon dioxide and 3 moles of hydrogen. The Ru−H species ( Cy2 NNN)RuCl(H) plays a decisive role in the unprecedented selectivity toward FA. In its choice to undergo a σ-bond metathesis either with the O−H of methanol (that completes the FA cycle) or with the O−H of FA that leads to carbon dioxide, it chooses the former as it is kinetically more favored by 4.58 kcal/mol. The current catalytic system comprising of NNN pincer-ruthenium phosphines based on bis(imino)pyridine ligands that gives high yields of H 2 and FA at unprecedented selectivity at low operating temperature offers immense promise in the transformation of methanol to clean-burning hydrogen and high-value FA.

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Section: Results and Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Pincer–Ruthenium-Catalyzed Reforming of Methanol─Selective High-Yield Production of Formic Acid and Hydrogen

et al. 2023

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“…In a recent report, a homogeneous (NNN)Ru pincer catalyst was used to obtain 62% ethanol conversion with a 45% yield of n-butanol. When a modified NNN ligand was used to anchor the Ru catalyst to a support, a 27% butanol yield with 35% conversion was achieved (77% selectivity) . Unfortunately, it was not possible to recycle the supported catalyst.…”

Section: Introductionmentioning

confidence: 99%

Ethanol Upgrading ton-Butanol Using Transition-Metal-Incorporated Poly(triazine)imide Frameworks

Cypher,

Pauly,

Castro

et al. 2023

ACS Appl. Mater. Interfaces

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The upgrading of ethanol to n-butanol was performed using a molecular catalyst integrated into a carbon nitride support, one of the first examples of a supported molecular catalyst performing the Guerbet process. Initial studies using crystalline poly(triazine)imide (PTI) with lithium or transition-metal cations imbedded in the support together with a base as the catalyst system did not produce any significant amounts of n-butanol. However, when using the catalyst material formed by treatment of PTI-LiCl with [(Cp*)IrCl2]2 (Cp* = pentamethylcyclopentadienyl) along with sodium hydroxide, a 59% selectivity for butanol (13% yield) was obtained at 145 °C. This PTI-(Cp*)Ir material exhibited distinct UV–vis absorption features and powder X-ray diffractions which differ from those of the parent PTI-LiCl and [(Cp*)IrCl2]2. The PTI-(Cp*)Ir material was found to have a metal loading of 27% iridium per empirical unit of the framework. Along with the formation of n-butanol from the Guerbet reaction, the presence of higher chain alcohols was also observed.

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Valorization of Lignocellulosic Molecules through Homogeneous Ru‐Catalyzed C−C and C−N Bond Forming Reactions

Fiorito,

Ferraccioli

2024

ChemistrySelect

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A sustainable upgrading of renewable bulk materials, obtained by decomposition of biomass lignocellulose, could facilitate their use in the industrial production of chemicals. Homogeneous ruthenium catalysis plays a fundamental role in this area. The review deals with the upgradation of lignocellulosic molecules through the formation of new C−C and C−N bonds. Selected examples of catalytic bond forming reactions reported until mid of 2023, include: (a) dehydrogenative based couplings of alcohols, (b) reductive amination of carbonyl compounds, (c) direct C−H functionalization of (hetero)aromatic compounds. These approaches fulfill the requirements of sustainability: application occurs without any previous substrate activation, thus reducing the production of waste. New chemicals containing the intrinsic molecular structure of lignocellulose substrates, showed a broad range of applications: green fuels, hydrogen carriers, monomers of polymers, intermediates of fine chemicals and pharmaceuticals. The results discussed in the review could inspire the reader to improve the valorization process, in terms of bio‐substrate scope as well as product complexity, through more strategic applications of the catalytic methods.

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Microwave-assisted pincer-ruthenium catalyzed Guerbet reaction for the upgradation of bio-ethanol to bio-butanol

Abstract: The upgradation of feed agnostic bio-ethanol to fuel grade n-butanol has been accomplished via the pincer-ruthenium catalyzed Guerbet reaction under microwave irradiation (75 W, 110 °C) with high efficiency after...

Cited by 9 publications

References 64 publications

Pincer–Ruthenium-Catalyzed Reforming of Methanol─Selective High-Yield Production of Formic Acid and Hydrogen

Pincer–Ruthenium-Catalyzed Reforming of Methanol─Selective High-Yield Production of Formic Acid and Hydrogen

Ethanol Upgrading ton-Butanol Using Transition-Metal-Incorporated Poly(triazine)imide Frameworks

Valorization of Lignocellulosic Molecules through Homogeneous Ru‐Catalyzed C−C and C−N Bond Forming Reactions

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