Direct Hydrogen Transfer Research Articles

Mn2(CO)10-catalyzed direct protic hydrogen transfer with unactivated alkenes

Transition-metal-catalyzed hydrogen-atom-transfer (HAT) reactions have proven to be effective strategies for obtaining important heterocycle scaffolds found in natural products. However, the electronic mismatch between metal catalysts and the protic hydrogen atom necessitates the use of excess oxidants and external reductive hydrogen sources in existing methods, which limit their practicality. To address this issue, we present a practical and efficient methodology for Mn₂(CO)₁₀-catalyzed intramolecular transfer of the protic hydrogen atom. A catalytic amount of tBuOOH is utilized promoting the HAT process, going beyond mere oxidation, thereby obviating the need for excess oxidants and external reductive hydrogen sources during the HAT process. Additionally, the dimeric manganese catalysis enables efficient dioxygenation, oxy-amination, oxy-sulfuration, and oxy-halogenation of alkenes. Comprehensive mechanistic studies have been done and suggest that a radical reaction pathway is involved in the proton transfer. This finding provides novel insights into the direct metal-catalyzed protic hydrogen atom-transfer reactions.

Ethanol-type anaerobic digestion enhanced methanogenic performance by stimulating direct interspecies electron transfer and interspecies hydrogen transfer

Ethanol pre-fermentation of food waste effectively alleviates acidification; however, its effects on interspecies electron transfer remain unknown. This study configured the feed according to COD ratios of ethanol: sodium acetate: sodium propionate: sodium butyrate of 5:2:1.5:1.5 (ethanol-type anaerobic digestion) and 0:5:2.5:2.5 (control), and conducted semi-continuous anaerobic digestion (AD) experiments. The results showed that ethanol-type AD increased maximum tolerable organic loading rate (OLR) to 6.0 gCOD/L/d, and increased the methane production by 1.2–14.8 times compared to the control at OLRs of 1.0–5.0 gCOD/L/d. The abundance of the pilA gene, which was associated with direct interspecies electron transfer (DIET), increased by 5.6 times during ethanol-type AD. Hydrogenase genes related to interspecies hydrogen transfer (IHT), including hydA-B, hoxH-Y, hnd, ech, and ehb, were upregulated during ethanol-type AD. Ethanol-type AD improved methanogenic performance and enhanced microbial metabolism by stimulating DIET and IHT.

Metal-acid synergistic catalysis accelerates the hydrogen borrowing amination of alcohols by confining Ru sites in Beta zeolite

Direct hydrogen transfer amination of alcohols with amines is an environmentally friendly and atom-economical route for the synthesis of N-alkylamines. Noble metal species are highly catalytic active sites, but the exorbitant price makes the urgency to boost the atom efficiency with stable recyclability. Herein, we demonstrated that encapsulation of Ru nanoparticles (NPs) within BEA zeolite through direct hydrothermal approach greatly promoted the catalytic efficiency in the N-alkylation of aromatic alcohols and amines under additive- and solvent-free conditions, resulting in the high yield (∼93 %), maximum turnover number (TON) of 12,822 and turnover frequency (TOF) of 9012 h−1, with stable recyclability and extendable substrate scope. The kinetic studies and in-situ characterizations revealed that the synergy of confined Ru NPs and adjacent acid sites of BEA zeolite significantly promoted the C–H bond activation in the rate-determining step of alcohol dehydrogenation into aldehydes. Besides, the acid sites also accelerated the condensation of aldehyde intermediates and anilines to promote the kinetic equilibrium, while the moderate strength of the Ru–H bond resulting from the confined Ru NPs is advantageous to balance the dehydrogenation and hydrogenation steps to reach the fascinating H-transfer process.

Porous Composite‐Mediated Bimetallic Cluster POMs/Zr‐MOF for Catalytic Transfer Hydrogenation of Biomass‐Derived Aldehydes and Ketones

AbstractSynergistic catalytic effects and metal node modulation are pivotal to the performance of multifunctional catalysts.We present a versatile strategy for constructing bimetallic M1M2 cluster catalysts (polyoxometalates (POMs)/Zr‐based metal‐organic frameworks (Zr‐MOF); M1 = Zr; M2 = W, V, Mo) by a microwave‐assisted in‐situ precoordination‐postmodification approach, which consisted of the grafting of POM single clusters onto Zr–O clusters of hierarchical porous composites (defective Zr‐MOF (HUiO‐66x)) and the modulation of metal nodes in Zr‐MOF. Hierarchical porosity and double active centers in the POMs/Zr‐MOF result in greater accessibility to catalytic sites and adjustable acid–base properties, thus providing opportunities for the catalytic transfer hydrogenation of biomass‐derived aldehydes/ketones. The synergistic acid–base couple sites (W6+–O2−–Zr4+) not only bridge hydrogen donors into the reaction system but also promote the dissociation of α‐C(sp3)‐H from isopropanol and subsequent hydrogen transfer to the activated carbonyl in furfural. Enhanced substrate adsorption and decreased activation barrier of the rate‐determining step are keys for the direct hydrogen transfer from carbonyl compounds to near‐quantitative corresponding alcohols via an eight‐membered‐ring transition state to achieving unprecedented low‐temperature catalytic performance over bimetallic Zr–W clusters. The proposed general method of bimetallic cluster catalysts reveals the roles of accessible metal modulation and synergistic catalytic centers toward specific catalysis.

Carbohydrates generated via hot water as catalyst for CO2 reduction reaction

Combining terrestrial biomass with submarine-type hydrothermal environments for CO2 reduction is a possible approach for realizing new energies while achieving sustainable circulation of carbon. Herein, carbohydrate-enabled CO2 reduction based on NaHCO3 conversion to formate revealed that hydrothermal environments facilitated direct hydrogen transfer from carbohydrates (glucose, cellulose) to CO2/NaHCO3 with hot water (250–300 °C, 5–20 MPa) acting as homogeneous catalyst in absence of any conventional catalysts giving CO2/NaHCO3 reduction efficiencies as high as 76% for cellulose. Time-resolved operando hydrothermal DRIFTS spectra of glycolaldehyde in hot water (250 °C, autogenous pressure) verified that water catalyzed NaHCO3 reduction by converting the -CHO group in the carbohydrate to its hydrated state as -CH(OH)2, which enabled NaHCO3 reduction by direct hydrogen transfer and that the ratio of hydrogen transfer from water:glycolaldehyde for NaHCO3 reduction was about 13:87 on an atom basis. For cellulose exploited as energy input, a greater than 3.4% solar-to-formate efficiency can be theoretically attained, which is unprecedented compared with present literature values. These findings provide basic data for future studies on biomass-enabled CO2 reduction and broaden the scope of hydrothermal chemistry for developing net-zero emission processes.

Mechanism of Catalytic Transfer Hydrogenation for Furfural Using Single Ni Atom Catalysts Anchored to Nitrogen-Doped Graphene Sheets.

Catalytic transfer hydrogenation (CTH) of α,β-unsaturated aldehydes using single metal atom catalysts supported on nitrogen-incorporated graphene sheet (M-Nx-Gr) materials has attracted increasing attention recently, yet the reaction mechanism remains to be explored. Compared to the Ni-N4-Gr model in which the dissociation of isopropanol is highly unfavorable as a result of steric hindrance and inertness of the Ni-N4 site embedded in graphene, the Ni-N3 site in Ni-N3-Gr is more active and facilitates the formation of *H with isopropanol as the H donor, where the dissociation of H from isopropanol with an energy barrier of 0.83 eV is the rate-determining step. An alternative reaction path starts from the coadsorption of isopropanol and furfural molecules at the Ni-N3 site, followed by a direct hydrogen transfer between the two molecules; however, the rate-determining step has a much higher energy barrier of 1.32 eV. Our calculations suggest that the hydrogenation of the aldehyde group is kinetically more favorable than the C═C hydrogenation, revealing the high chemoselectivity of furfural to furfuryl alcohol. Our investigations reveal that the CTH mechanism using the Ni-N3-Gr catalyst is different from that on traditional metal oxides, where the former has only one single active site, while two active sites are required for the latter. The proposed reaction mechanism of CTH for furfural in this study should be helpful to guide the design of single metal atom catalysts with appropriate N coordination for application in chemoselective hydrogenation reactions.

Gliding on Ice in Search of Accurate and Cost-Effective Computational Methods for Astrochemistry on Grains: The Puzzling Case of the HCN Isomerization.

The isomerization of hydrogen cyanide to hydrogen isocyanide on icy grain surfaces is investigated by an accurate composite method (jun-Cheap) rooted in the coupled cluster ansatz and by density functional approaches. After benchmarking density functional predictions of both geometries and reaction energies against jun-Cheap results for the relatively small model system HCN···(H2O)2, the best performing DFT methods are selected. A large cluster containing 20 water molecules is then employed within a QM/QM′ approach to include a realistic environment mimicking the surface of icy grains. Our results indicate that four water molecules are directly involved in a proton relay mechanism, which strongly reduces the activation energy with respect to the direct hydrogen transfer occurring in the isolated molecule. Further extension of the size of the cluster up to 192 water molecules in the framework of a three-layer QM/QM′/MM model has a negligible effect on the energy barrier ruling the isomerization. Computation of reaction rates by the transition state theory indicates that on icy surfaces, the isomerization of HNC to HCN could occur quite easily even at low temperatures thanks to the reduced activation energy that can be effectively overcome by tunneling.

Hydrogen removal in circulating vacuum degasser under conditions of PJSC “NLMK”

For high­quality steel smelting, stage­by­stage production is required, which has a complex of metallurgical units capable for producing products with high performance properties and low content of harmful impurities. One of the harmful impurities is hydrogen, so it is important to limit its content in the metal. To ensure the specifed hydrogen content, the metal in the steel out­of­furnace treatment at Converter Shop No. 2 (CS­2) of PJSC “Novolipetsk Metallurgical Plant” (“NLMK”) is subjected to vacuum treatment in a circulating vacuum degasser. Despite the prevalence of circulating vacuum derassers, theoretically, mechanism of hydrogen removal in these metallurgical units has been insufciently studied. To increase efciency of hydrogen removal, theoretical calculations were performed to remove it from the metal. There are several mechanisms for hydrogen removing: direct transfer of hydrogen from metal to the surrounding space; formation of gas bubbles in metal and their direct ascent; nucleation of hydrogen bubbles at the border of refractory wall and metal; removal of hydrogen by metal blowing with neutral gas (argon). It is shown that the main ways of hydrogen removal in a circulating vacuum degasser are direct transfer of hydrogen from metal to the surrounding space and blowing of melt with transporting gas. In the CS­2 of PJSC “NLMK”, both ways are implemented at a circulating vacuum degasser. Vacuum pumps provide pressure in a vacuum chamber of less than 101.3 Pa (0.001 atm.). It promotes intensive removal of hydrogen from the metal surface. To ensure circulation of metal, transporting gas argon is supplied to the inlet pipe of the RH degasser, which also takes part in removal of dissolved gases by transferring hydrogen to neutral gas bubbles. Additionally, performed calculations have shown that the main way of degassing in conditions of CS­2 of PJSC “NLMK” is removal of hydrogen into the bubbles of carrier gas.

Hydrogen Removal in Circulating Vacuum Degasser under Conditions of PJSC “NLMK”

For high-quality steel smelting, stagebystage production is required, which has a complex of metallurgical units capable for producing products with high performance properties and low content of harmful impurities. One of the harmful impurities is hydrogen, so it is important to limit its content in the metal. To ensure the specified hydrogen content, the metal in the steel outoffurnace treatment at Converter Shop No. 2 (CS2) of PJSC “Novolipetsk Metallurgical Plant” (“NLMK”) is subjected to vacuum treatment in a circulating vacuum degasser. Despite the prevalence of circulating vacuum degassers, theoretically, mechanism of hydrogen removal in these metallurgical units has been insufficiently studied. To increase efficiency of hydrogen removal, theoretical calculations were performed to remove it from the metal. There are several mechanisms for hydrogen removing: direct transfer of hydrogen from metal to the surrounding space; formation of gas bubbles in metal and their direct ascent; nucleation of hydrogen bubbles at the border of refractory wall and metal; and removal of hydrogen by metal blowing with neutral gas (argon). It is shown that the main ways of hydrogen removal in a circulating vacuum degasser are direct transfer of hydrogen from metal to the surrounding space and blowing of melt with transporting gas. In the CS2 of PJSC “NLMK”, both ways are implemented at a circulating vacuum degasser. Vacuum pumps provide pressure in a vacuum chamber of less than 101.3 Pa (0.001 atm). It promotes intensive removal of hydrogen from the metal surface. To ensure circulation of metal, transporting gas argon is supplied to the inlet pipe of the RH degasser, which also takes part in removal of dissolved gases by transferring hydrogen to neutral gas bubbles. Additionally, performed calculations have shown that the main way of degassing in conditions of CS2 of PJSC “NLMK” is removal of hydrogen into the bubbles of carrier gas.

Study on 5-nitro-2,4-dihydro-3H-1,2,4-triazol-3-one (NTO) decomposition using online photoionization mass spectrometry and theoretical simulations

5-Nitro-2,4-dihydro-3H-1,2,4-triazol-3-one (NTO) is a representative and insensitive energetic compound mainly used as a component of low vulnerable ammunition, but its decomposition process is not clear up to date. Herein, online photoionization mass spectrometry combined with theoretical simulations was employed to shed light on the thermal decomposition mechanism of NTO. The experimental and calculated results provide evidences for the thermal decomposition of NTO through direct ring rupture and intermolecular hydrogen transfer pathways. The initial decomposition step of NTO single molecule is direct ring rupture, followed by NO2 removal. The remaining structure undergoes C-N bond cleavage leading to HN2 dissociation, the CONCH finally decomposes into CO and HCN. The major products of NTO decomposition include N2, CO2, H2N2, NH3, and the minor products are HN2, H3N3, H2O, which is basically consistent with experiments. The formation mechanism of decomposition products is also discussed in detail and the total decomposition pathways are constructed.

Copper-nickel mixed oxide catalysts from layered double hydroxides for the hydrogen-transfer valorisation of lignin in organosolv pulping

Copper and nickel mixed catalysts obtained by calcination of iron and aluminium hydrotalcites (layered double hydroxides, LDH) have been tested in the conversion of a lignin model dimer in subcritical methanol. Phase distribution and textural properties of the catalysts were characterized by X-ray diffraction Rietveld analysis and N2 physisorption. The presence of copper was critical for effective hydrogenation, both by direct hydrogen transfer from methanol to aldehyde groups and by reactivity of products from methanol reforming. TPR experiments showed that the hydrogenation activity was promoted by an enhanced reducibility of the Cu-catalysts, related to the presence of other oxide components.Characterisation of the catalysts after reaction indicated that metallic copper was formed by the reduction of CuO by methanol and that modifications of the oxide catalysts in the reaction medium played a major role in the formation of active sites.

Insights into Ethanol Coupling over Hydroxyapatite using Modulation Excitation Operando Infrared Spectroscopy

AbstractThe coupling of biomass‐derived ethanol to n‐butanol is a topic of contemporary interest. Indeed, n‐butanol can not only be used as a higher energy‐density fuel additive, it is also a key component in perfumes and serves as a solvent for paints and dyes. Hydroxyapatite (HAP) emerged in the literature as a promising catalysts for this transformation, with n‐butanol selectivity reaching ∼75 % at 10 % ethanol conversion. However, the molecular‐level mechanism for this reaction is still unclear and several mechanistic questions remain unanswered. Here, we use diffuse reflectance infrared Fourier Transform spectroscopy, coupled with mass spectrometry following a modulation excitation approach (ME‐DRIFTS‐MS) that enables us to better understand the dynamic processes involved. Our approach allows for a vibrational characterization of the active surface species and the formulation of a consistent mechanism. Based on our experimental observations, Ca2+/OH− can be put forward as the main active site for the aldol condensation. POH/OH− acid‐base pair is proposed as the active site for the Meerwein‐Ponndorf‐Verley (MPV) direct hydrogen transfer of the aldol condensation product, crotonaldehyde.

Manganese catalyzed transfer hydrogenation of biomass-derived aldehydes: Insights to the catalytic performance and mechanism

Manganese catalyzed transfer hydrogenation (CTH) of aldehydes is an attractive method for the synthesis of alcohols. Here, we report a novel and efficient MnO@C-N catalyst for the CTH of biomass-derived 5-hydroxymethylfurfural and other aldehydes to alcohols in high yields. Catalytic experimental studies showed that the MnO and nitrogen-doping are responsible for the high selectivity and high conversion, respectively. Isotopic labelling experiments demonstrated that the CTH of aldehydes to alcohols over MnO@C-N is via a route by direct hydrogen transfer. Kinetic studies revealed that the N-doping can improve the reaction rate and reduce the activation energy of the aldehydes conversion. DFT calculations also indicated that both pyridine N and pyrrolic N doping can reduce the energy barrier for acetone desorption by the interaction between N and hydroxyl-H of alcohol. Furthermore, MnO@C-N showed good recyclability for at least five reaction cycles. We anticipate that these results can drive progress in the manganese catalyzed transfer hydrogenation reaction.

Allyl alcohol production by gas phase conversion reactions of glycerol over bifunctional hierarchical zeolite-supported bi- and tri-metallic catalysts

The gas-phase conversion of glycerol into allyl alcohol over Fe–Mo and Cs–Fe–Mo/HZSM-5 (with SiO2/Al2O3 = 30 and 1500) zeolite catalysts in a packed-bed continuous flow reactor has been reported for the first time. To the best of our knowledge, the Cs–Fe–Mo/HZSM-5 catalyst appears to be most promising for gas-phase conversion of glycerol into allyl alcohol. The structure and catalytic performance for the glycerol conversion over bi- and tri-metallic-promoted zeolite catalysts were studied. The synthesized catalysts were characterized by ICP–AES, ICP–MS, N2 physisorption, SEM, STEM–EDX, XRD, NH3–TPD, CO2–TPD, XPS, TGA and pyridine-DRIFT techniques, which showed that differences in catalysts activity and product distribution are influenced by metal loading, changes of acid-base, and porosity. The most stable allyl alcohol selectivity achieved was 46.1 mol.% at 98.1 mol.% glycerol conversion over the 5wt.%Cs–2.5wt.%Fe–2.5wt.%Mo/HZSM-5 (SiO2/Al2O3 = 1500) catalyst achieved with 10 wt% glycerol feed at 350 °C reaction temperature after 26 h time-on-stream. The superior performance of the synthesized catalyst was attributed to the presence of the basic sites, high mesopore volume and mesopore surface area, balance between acidic-basic sites, synergetic interaction between metal species and ZSM-5 zeolite support. The reaction pathway mechanisms of glycerol to value-added allyl alcohol via the direct glycerol dehydration and hydrogen transfer mechanism over basic sites are proposed.

One‐Pot Transfer Hydrogenation of methyl levulinate into valerolactone and 1,4‐pentanediol over in situ Reduced Cu/ZrOCO3 in 2‐PrOH

AbstractIn this work, a simple and economical process, the reduction preparation of the Cu/ZrOCO3 catalyst and the catalytic transfer hydrogenation (CTH)reaction of methyl levulinate (ML)were carried out simultaneously in one pot providing 89.79% product yield at 180 ° C for 7 h. Different from direct hydrogen transfer reaction catalyzed by ZrOCO3 with only valerolactone (GVL) produced, the introduction of Cu/Cu+ on ZrOCO3 carrier not only enhances the activity of the reaction, but also further converts GVL into 1,4‐pentanediol (1,4‐PDO)by indirect hydrogen transfer. In addition, we also found the copper‐loaded amphoteric carrier has better catalytic activity than the basic carrier.

Mechanistic dichotomies in redox reactions of mononuclear metal-oxygen intermediates.

There are mechanistic dichotomies with regard to the formation, electronic structures and reaction mechanisms of metal-oxygen intermediates, since these metal-oxygen species could be composed of different resonance structures or canonical structures of the oxidation states of metals and ligands, which may undergo different reaction pathways. Even the same metal-oxygen intermediates, such as metal-oxo species, may undergo an electron-transfer pathway or a direct hydrogen or oxygen atom transfer pathway depending on the one-electron redox potentials of metal-oxo species and substrates. Electron-transfer pathways are also classified into two mechanisms, such as outer-sphere and inner-sphere pathways. The one-electron redox potentials of metal-oxygen species and substrates are also shifted because of the binding of acids, which can result from either hydrogen bonding or protonation. There are a rebound pathway and a non-rebound pathway following the initial electron transfer or hydrogen atom transfer step to produce hydroxylated products, depending on the one-electron redox potentials of metal-oxo species and substrates. Nucleophilic reactions can be switched to electrophilic pathways, depending on reaction conditions such as reaction temperature. Spin states of metal-oxygen intermediates are also an important factor that controls the redox reactivity of oxidants in oxidation reactions. Here, we review such various mechanistic dichotomies in redox reactions of metal-oxygen intermediates with the emphasis on understanding and controlling the redox reactivity of metal-oxygen intermediates from experimental and theoretical points of view.

Zirconium–lignosulfonate polyphenolic polymer for highly efficient hydrogen transfer of biomass-derived oxygenates under mild conditions

Both value-added utilization of low-rank renewable feedstocks to prepare catalytic materials and selective transformation of bioderived aldehydes are very attractive topics. Herein, lignosulfonate, a waste by-product from the paper industry, was simply assembled with ZrCl4 under non-toxic hydrothermal conditions for scalable preparation of Zr-containing polyphenolic biopolymer catalysts (ZrLS). Systematic characterizations indicated that the strong coordination between Zr4+ and phenolic hydroxyl groups in lignosulfonate led to the formation of strong Lewis acid-base couple sites (Zr4+−O2−) and porous inorganic-organic framework structure (mesopores centered at 6.1 nm), while the inherent sulfonic groups in lignosulphonate could serve as Brønsted acidic sites. The cooperative role of these versatile acid−base sites in ZrLS afforded excellent catalytic performance for Meerwein-Ponndorf-Verley (MPV) reaction of a broad range of bioderived platform chemicals under mild conditions (80 °C), especially of furfural (FF) to furfuryl alcohol (FA), in quantitative yields (96%) with high FA formation rate of 9600 μmol g−1 h−1 and TOF of 4.37 h−1. Kinetic studies revealed that the activation energy of the MPV reduction of FF was as low as 52.25 kJ/mol, accounting for the high reaction rate. Isotopic labelling experiments demonstrated direct hydrogen transfer from the α-C of 2-PrOH to the α-C of FF on acid-base sites was the rate-determining step. Moreover, ZrLS showed good recyclability for at least seven reaction cycles.

Mechanistic Insights into the Nickel-Catalyzed Cross-Coupling Reaction of Benzaldehyde with Benzyl Alcohol via C–H Activation: A Theoretical Investigation

With the aid of density functional theory (DFT) calculations, mechanistic investigations have been carried out for the nickel-catalyzed dehydrogenative cross-coupling reaction of benzaldehyde with benzyl alcohol in the presence of N-heterocyclic carbene (NHC) ligand. The overall Ni(0)/Ni(II) catalytic cycle consists of four basic steps: ligand exchange, oxidative addition, hydrogen transfer, and reductive elimination. Considerable interests are paid on detecting the transition state of the rate-determining step, with particular emphasis on the structural and electronic properties, together with clarifying the important roles of external oxidant and hydrogen acceptor. The hydrogen transfer process in the oxidative addition step is rate-determining in the whole catalytic cycle, which is accomplished by C-Ha (active Ha) activation without generating the high energy nickel hydride intermediate. Such process could be understood as the direct hydrogen transfer, instead of general concerted oxidative addition to low valent transition metal. The analysis of the bond distances, electrondistributions, and orbital interactions highlights the direct hydrogen transfer mechanism. Furthermore, by exploring the influences from the electronic effect of different substrates on the reaction energy barriers, the a,a,a-trifluoroacetophenone could accelerate the direct hydrogen transfer with low activate energy.

Catalytic Transfer Hydrogenation of Biomass-Derived Carbonyls over Hafnium-Based Metal-Organic Frameworks.

A series of highly crystalline, porous, hafnium-based metal-organic frameworks (Hf-MOFs) have been shown to catalyze the transfer hydrogenation reaction of levulinic ester to produce γ-valerolactone by using isopropanol as a hydrogen donor. The results are compared with their zirconium-based counterparts. The role of the metal center in Hf-MOFs has been identified and reaction parameters optimized. NMR studies using isotopically labeled isopropanol provide evidence that the transfer hydrogenation occurs through a direct intermolecular hydrogen transfer route. The catalyst, Hf-MOF-808, can be recycled several times with only a minor decrease in catalytic activity. The generality of the procedure has been demonstrated by accomplishing the transformation with aldehydes, ketones, and α,β-unsaturated carbonyl compounds. The combination of Hf-MOF-808 with the Brønsted-acidic Al-Beta zeolite gives the four-step one-pot transformation of furfural to γ-valerolactone in good yield of 75 %.

Orderly Layered Zr-Benzylphosphonate Nanohybrids for Efficient Acid-Base-Mediated Bifunctional/Cascade Catalysis.

The development of functional metal-organic materials that are robust and active for bifunctional/cascade catalysis is of great significance. Herein, a series of mesoporous and orderly layered nanohybrids were synthesized for the first time through simple and template-free assembly of ortho-, meta-, or para-xylylenediphosphonates (o-, p-, or m-PhP) containing zirconium. It was found that m-PhPZr nanoparticles (20-50 nm) with mesopores centered at 7.9 nm and high Lewis acid-base site ratio (1:0.7) showed excellent performance under mild conditions (as low as 82 °C) in transfer hydrogenation of carbonyl compounds, including bioaldehydes and alcohols, with near quantitative yields and little Zr leaching. Isotopic labeling studies indicated the occurrence of direct hydrogen transfer rather than metal hydride route by bifunctional catalysis. Lewis acidic (Zr) and basic (PO3 ) centers of the heterogeneous catalyst were further revealed to play a synergistic role in one-pot cascade transformations, for example, of ethyl levulinate to γ-valerolactone and glucose to 5-hydroxymethylfurfural.