Hydrogenation Of Olefins Research Articles

Diastereoselective Hydrogenation of Tetrasubstituted Olefins using a Heterogeneous Pt-Ni Alloy Catalyst.

Stereoselective hydrogenation of tetrasubstituted olefins is an attractive method to access compounds with two contiguous stereocenters. However, homogeneous catalysts for enantio- and diastereoselective hydrogenation exhibit low reactivity toward tetrasubstituted olefins due to steric crowding between the ligand scaffold and the substrate. Monometallic heterogeneous catalysts, on the other hand, provide accessible surface active sites for hindered olefins but exhibit unpredictable and inconsistent stereoinduction. In this work, we develop a Pt-Ni bimetallic alloy catalyst that can diastereoselectively hydrogenate unactivated, sterically-bulky tetrasubstituted olefins, utilizing the more oxophilic Ni atoms to adsorb a hydroxyl directing group and direct facially-selective hydrogen addition to the olefin via the Pt atoms. Structure-activity studies on several Pt-Ni compositions underscore the importance of exposing a uniform PtNi alloy surface to achieve high diastereoselectivity and minimize side reactions. The optimized Pt-Ni/SiO2 catalyst exhibits good functional group tolerance and broad scope for tetrasubstituted olefins in a cyclopentene scaffold, generating cyclopentanol products with three contiguous stereocenters. The synthetic utility of the method is demonstrated in a four-step synthesis of (1R,2S)-(+)-cis-methyldihydrojasmonate with high yield and enantiopurity.

Synergistic effect between amorphous ZrO2 modified support and Pd catalyst: Unveiling superlative sulfur resistance and exquisite catalytic hydrogenation performance

The presence of sulfides in the reaction system can seriously affect the stability and activity of the catalysts. In this paper, we compare the impact of introducing varying amounts of the metal oxide ZrO2 on the hydrogenation activity and sulfur resistance of Pd-based catalysts. The study examined the effect of calcination temperature for catalysts and various organic sulfide types on their catalytic performance. We employed multiple techniques to characterize the catalysts, including physical adsorption, TEM, XRD, XPS, H2-TPD, NH3-TPD, and Py-IR. The results revealed that the catalysts achieved 99.9 % conversion and exhibited 99.5 % selectivity towards 4-ethyltoluene when the Pd and Zr molar ratio was 1:5. Furthermore, they could withstand the presence of toxicants for over 10 cycles. The main reason for the difference in activity and stability between catalysts lies in introducing ZrO2 as a promoter. This introduction increases the number of acidic sites and enhances the electronic effect, thereby facilitating the cleavage of H2 by Pd0. The synergistic effect between Pd and ZrO2 decreases the strength of S-Me, impedes sulfide adsorption, and improves the sulfur resistance stability of the catalyst. This work demonstrates that ZrO2-modified Pd-based catalysts have great potential in the anti-sulfur system of olefin hydrogenation.

Cross-Linked Polyolefins through Tandem ROMP/Hydrogenation.

Cross-linked polyolefins have important advantages over their thermoplastic analogues, particularly improved impact strength and abrasion resistance, as well as increased chemical and thermal stability; however, most strategies for their production involve postpolymerization cross-linking of polyolefin chains. Here, a tandem ring-opening metathesis polymerization (ROMP)/hydrogenation approach is presented. Cyclooctene (COE)-co-dicyclopentadiene (DCPD) networks are first synthesized using ROMP, after which the dispersed Ru metathesis catalyst is activated for hydrogenation through the addition of hydrogen gas. The reaction temperature for hydrogenation must be sufficiently high to allow mobility within the system, as dictated by thermal transitions (i.e., glass and melting transitions) of the polymeric matrix. COE-rich materials exhibit branched-polyethylene-like crystallinity (25% crystallinity) and melting points (Tm = 107 °C), as well as excellent ductility (>750% extension), while majority DCPD materials are glassy (Tg = 84 °C) and much stiffer (E = 710 MPa); all materials exhibit high tensile toughness. Importantly, hydrogenation of olefins in these cross-linked materials leads to notable improvements in oxidative stability, as saturated networks do not experience the same substantial degradation of mechanical performance as their unsaturated counterparts upon prolonged exposure to air.

Reversible Intrapore Redox Cycling of Platinum in Platinum-Ion-Exchanged HZSM-5 Catalysts.

Isolated platinum(II) ions anchored at acid sites in the pores of zeolite HZSM-5, initially introduced by aqueous ion exchange, were reduced to form platinum nanoparticles that are stably dispersed with a narrow size distribution (1.3 ± 0.4 nm in average diameter). The nanoparticles were confined in reservoirs within the porous zeolite particles, as shown by electron beam tomography and the shape-selective catalysis of alkene hydrogenation. When the nanoparticles were oxidatively fragmented in dry air at elevated temperature, platinum returned to its initial in-pore atomically dispersed state with a charge of +2, as shown previously by X-ray absorption spectroscopy. The results determine the conditions under which platinum is retained within the pores of HZSM-5 particles during redox cycles that are characteristic of the reductive conditions of catalyst operation and the oxidative conditions of catalyst regeneration.

Diastereoselective Hydrogenation of Tetrasubstituted Olefins using a Heterogeneous Pt‐Ni Alloy Catalyst

AbstractStereoselective hydrogenation of tetrasubstituted olefins is an attractive method to access compounds with two contiguous stereocenters. However, homogeneous catalysts for enantio‐ and diastereoselective hydrogenation exhibit low reactivity toward tetrasubstituted olefins due to steric crowding between the ligand scaffold and the substrate. Monometallic heterogeneous catalysts, on the other hand, provide accessible surface active sites for hindered olefins but exhibit unpredictable and inconsistent stereoinduction. In this work, we develop a Pt−Ni bimetallic alloy catalyst that can diastereoselectively hydrogenate unactivated, sterically‐bulky tetrasubstituted olefins, utilizing the more oxophilic Ni atoms to adsorb a hydroxyl directing group and direct facially‐selective hydrogen addition to the olefin via the Pt atoms. Structure‐activity studies on several Pt−Ni compositions underscore the importance of exposing a uniform PtNi alloy surface to achieve high diastereoselectivity and minimize side reactions. The optimized Pt−Ni/SiO2 catalyst exhibits good functional group tolerance and broad scope for tetrasubstituted olefins in a cyclopentene scaffold, generating cyclopentanol products with three contiguous stereocenters. The synthetic utility of the method is demonstrated in a four‐step synthesis of (1R,2S)‐(+)‐cis‐methyldihydrojasmonate with high yield and enantiopurity.

The FeBr3-Catalyzed Transfer Hydrogenation of Styrene Derivatives under Mild Reaction Conditions

AbstractThe transfer hydrogenation of alkenes was realized by using a simple transition-metal compound (FeBr3) and 1,4-cyclohexadiene (1,4-CHD) as the hydrogen donor. The conversion of a number of di- and trisubstituted alkenes was investigated, and even a tetrasubstituted alkene was successfully converted. Compared with previously published work with the more expensive InBr3, the reaction times were considerably reduced and significantly milder reaction conditions could be applied. Interestingly, a transformation that was catalytic in 1,4-CHD, with molecular hydrogen as a stoichiometric reducing agent at 1 bar, was also accomplished.

Rational Design of Metallylenes for Hydrogenation Reactions

AbstractThe hydrogenation of alkenes, alkynes, carbonyls, and imines by H2‐activated metallylenes (H3C−EH2−L, CELH2; E=Si, Ge, Sn and L=NMe2, PMe2) was studied using relativistic density functional theory at ZORA‐BP86/TZ2P. By means of activation strain and Kohn–Sham molecular orbital analyses, the physical factors underlying the trends in reactivity were identified and quantified. Firstly, the hydrogenation reactivity increases on descending Group 14, that is from silylenes (E=Si) to stannylenes (E=Sn). This reactivity trend originates primarily from a reduced energy required to break the bonds between the Group 14 atom and the hydrogen atoms because the strength of these bonds decreases from Si−H to Ge−H to Sn−H. Secondly, the reactivity decreases as the Group 15 ligand changes from nitrogen to phosphorus (L=NMe2, PMe2) which stems from the trigonal pyramidal PMe2 geometry compared to the trigonal planar NMe2 geometry. The latter can, therefore, effectively engage in stronger orbital interactions with the substrate than the former, due to a more efficient HOMO–LUMO orbital overlap. By combining our insights, we rationally designed an optimally tuned catalyst (Group 14 atom and ligand) considering the overall catalytic cycle involving H2 activation of the metallylene and subsequent hydrogenation.

Mechanistic study of alkene hydrogenation catalyzed by cationic Ni(II)-hydride PNHP complexes – Ni(II/IV) vs. Ni(II) cycle

The hydrogenation mechanisms of alkenes catalyzed by square-planar cationic Ni(II)-PNHP hydride complexes have been computed (M06L-GD3-SCRF). It is found that the reaction prefers a non-bifunctional inner-sphere mechanism, the Ni(II)/Ni(IV) cycle involving H2 oxidative addition forming unusual Ni(IV) oxidation state and reductive elimination is accessible and has been proven to be superior or competitive with the widely accepted Ni(II) cycle undergoing concerted H2 σ-bond metathesis in formal Ni(II) oxidation state. Systematic investigations into the electronic and geometric effects of phosphine ligand substituents uncover their significant influence on the Gibbs free energy barrier of elementary steps, leading to differences in catalytic activity. Analysis into these effects demonstrates a strong correlation between the apparent free energy barrier and frontier orbital energy, natural charge of Ni-center and buried volume ratio of the catalyst. These findings offer valuable insights for the design of future catalysts.

Cobalt‐Catalyzed Hydrogenation and Deuteration Reactions of Bicyclic Alkenes in an Aqueous Environment

AbstractHerein, we report cobalt‐catalyzed hydrogenation and deuteration reactions of bicyclic alkenes using H2O and D2O as the sole hydrogen and deuterium sources, respectively, employing Zn or Mn as a metal reductant. Lewis‐acid co‐catalysts were found to promote the reaction whilst simultaneously catalyzing transesterification processes. Use of 1 atm of H2 allows for catalytic loading of the metal reductant. In all cases, the reaction operated with high functional‐group tolerance and produced reduced products in high yield.

Synthesis of Network Biobased Aliphatic Polyesters Exhibiting Better Tensile Properties than the Linear Polymers by ADMET Polymerization in the Presence of Glycerol Tris(undec-10-enoate).

Development of biobased aliphatic polyesters with better mechanical (tensile) properties in film has attracted considerable attention. This report presents the synthesis of soluble network biobased aliphatic polyesters by acyclic diene metathesis (ADMET) polymerization of bis(undec-10-enyl)isosorbide diester [M1, dianhydro-D-glucityl bis(undec-10-enoate)] in the presence of a tri-arm crosslinker [CL, glycerol tris(undec-10-enoate)] using a ruthenium-carbene catalyst, and subsequent olefin hydrogenation using RhCl(PPh3)3. The resultant polymers, after hydrogenation (expressed as HCP1) and prepared in the presence of 1.0 mol% CL, showed better tensile properties than the linear polymer (HP1) with similar molecular weight [tensile strength (elongation at break): 20.8 MPa (282%) in HP1 vs. 35.4 MPa (572%) in HCP1]. It turned out that the polymer films prepared by the addition of CL during the polymerization (expressed as a 2-step approach) showed better tensile properties. The resultant polymer film also shows better tensile properties than the conventional polyolefins such as linear high density polyethylene, polypropylene, and low density polyethylene.

Catalytic hydrogenation of olefins by a multifunctional molybdenum-sulfur complex

Exploration of molybdenum complexes as homogeneous hydrogenation catalysts has garnered significant attention, but hydrogenation of unactivated olefins under mild conditions are scarce. Here, we report the synthesis of a molybdenum complex, [Cp*Mo(Ph2PC6H4S−CH = CH2)(Py)]+ (2), which exhibits intriguing reactivity toward C2H2 and H2 under ambient pressure. This vinylthioether complex showcases efficient catalytic activity in the hydrogenation of various aromatic and aliphatic alkenes, demonstrating a broad substrate scope without the need for any additives. The catalytic pathway involves an uncommon oxidative addition of H2 to the cationic Mo(II) center, resulting in a Mo(IV) dihydride intermediate. Moreover, complex 2 also shows catalytic activity toward C2H2, leading to the production of polyacetylene and the extension of the vinylthioether ligand into a pendant triene chain.

Rhodium Complexes with a Pyridine-2-yloxy-silyl-Based N,Si-Ligand: Bonding Situation and Activity as Alkene Hydrogenation Catalysts

Rhodium Complexes with a Pyridine-2-yloxy-silyl-Based N,Si-Ligand: Bonding Situation and Activity as Alkene Hydrogenation Catalysts

Iridium-Catalyzed Enantioselective Transfer Hydrogenation of 1,1-Dialkylethenes with Ethanol: Scope and Mechanism.

Despite half a century's advance in the field of transition-metal-catalyzed asymmetric alkene hydrogenation, the enantioselective hydrogenation of purely alkyl-substituted 1,1-dialkylethenes has remained an unmet challenge. Herein, we describe a chiral PCNOx-pincer iridium complex for asymmetric transfer hydrogenation of this alkene class with ethanol, furnishing all-alkyl-substituted tertiary stereocenters. High levels of enantioselectivity can be achieved in the reactions of substrates with secondary/primary and primary/primary alkyl combinations. The catalyst is further applied to the redox isomerization of disubstituted alkenols, producing a tertiary stereocenter remote to the resulting carbonyl group. Mechanistic studies reveal a dihydride species, (PCNOx)Ir(H)2, as the catalytically active intermediate, which can decay to a dimeric species (κ3-PCNOx)IrH(μ-H)2IrH(κ2-PCNOx) via a ligand-remetalation pathway. The catalyst deactivation under the hydrogenation conditions with H2 is much faster than that under the transfer hydrogenation conditions with EtOH, which explains why the (PCNOx)Ir catalyst is effective for the transfer hydrogenation but ineffective for the hydrogenation. The suppression of di-to-trisubstituted alkene isomerization by regioselective 1,2-insertion is partly responsible for the success of this system, underscoring the critical role played by the pincer ligand in enantioselective transfer hydrogenation of 1,1-dialkylethenes. Moreover, computational studies elucidate the significant influence of the London dispersion interaction between the ligand and the substrate on enantioselectivity control, as illustrated by the complete reversal of stereochemistry through cyclohexyl-to-cyclopropyl group substitution in the alkene substrates.

A Powerful P-N Connection: Preparative Approaches, Reactivity, and Applications of P-Stereogenic Aminophosphines.

For more than five decades, P-stereogenic aminophosphine chalcogenides and boranes have attracted scientific attention and are still in the focus of ongoing research. In the last years, novel transition metal-based synthesis methods have been discovered, in addition to the long-known use of chiral auxiliaries. Enantiomerically pure compounds with N-P+-X- (X=O, S, BH3) motifs served as valuable reactive building blocks to provide new classes of organophosphorus derivatives, thereby preserving the stereochemical information at the phosphorus atom. Over the years, intriguing applications in organocatalysis and transition metal catalysis have been reported for some representatives. Asymmetric reductions of C=C, C=N, and C=O double bonds were feasible with selected P-stereogenic aminophosphine oxides in the presence of hydrogen transfer reagents. P-stereogenic aminophosphine boranes could be easily deprotected and used as ligands for various transition metals to enable catalytic asymmetric hydrogenations of olefins and imines. This review traces the emergence of a synthetically and catalytically powerful functional compound class with phosphorus-centered chirality in its main lines, starting from classical approaches to modern synthesis methods to current applications.

Structural and functional characterization of a new thermophilic-like OYE from Aspergillus flavus

Old yellow enzymes (OYEs) have been proven as powerful biocatalysts for the asymmetric reduction of activated alkenes. Fungi appear to be valuable sources of OYEs, but most of the fungal OYEs are unexplored. To expand the OYEs toolbox, a new thermophilic-like OYE (AfOYE1) was identified from Aspergillus flavus strain NRRL3357. The thermal stability analysis showed that the T1/2 of AfOYE1 was 60 °C, and it had the optimal temperature at 45 °C. Moreover, AfOYE1 exhibited high reduction activity in a wide pH range (pH 5.5–8.0). AfOYE1 could accept cyclic enones, acrylamide, nitroalkenes, and α, β-unsaturated aldehydes as substrates and had excellent enantioselectivity toward prochiral alkenes (> 99% ee). Interestingly, an unexpected (S)-stereoselectivity bioreduction toward 2-methylcyclohexenone was observed. The further crystal structure of AfOYE1 revealed that the “cap” region from Ala132 to Thr182, the loop of Ser316 to Gly325, α short helix of Arg371 to Gln375, and the C-terminal “finger” structure endow the catalytic cavity of AfOYE1 quite deep and narrow, and flavin mononucleotide (FMN) heavily buried at the bottom of the active site tunnel. Furthermore, the catalytic mechanism of AfOYE1 was also investigated, and the results confirmed that the residues His211, His214, and Tyr216 compose its catalytic triad. This newly identified thermophilic-like OYE would thus be valuable for asymmetric alkene hydrogenation in industrial processes.Key pointsA new thermophilic-like OYE AfOYE1 was identified from Aspergillus flavus, and the T1/2of AfOYE1 was 60 °CAfOYE1 catalyzed the reduction of 2-methylcyclohexenone with (S)-stereoselectivityThe crystal structure of AfOYE1 was revealedv

Asymmetric Autotandem Palladium Catalysis for α,β-Unsaturated Lactones: Merging Olefin and Ester Hydrogenation

Asymmetric Autotandem Palladium Catalysis for α,β-Unsaturated Lactones: Merging Olefin and Ester Hydrogenation

Hydrogenation of Cinnamaldehyde Using Carbon Dots Reduced Palladium Nanoparticles

Carbon dots (CDs) with a size range of 0.2 to 2 nm were prepared using a hydrothermal treatment of sucrose and oleic acid. The as-synthesized CDs were used to reduce H2PdCl4 to metallic Pd nanoparticles with dPd = 9.3 ± 3.7 nm, as confirmed by PXRD and HRTEM data. Pd particles were made to be larger than the CDs, to observe any inverse support effects, however, TEM data revealed that the CDs were transformed to carbon sheets in the reduction reaction at 100 °C. The synthesized Pd-CDs catalysts (0.81 wt. % loading) and CDs were both tested for the liquid phase hydrogenation of cinnamaldehyde. The influence of mass, temperature, and hydrogen flow rate on the activity and selectivity of the CDs and Pd-CDs catalyst on the hydrogenation of cinnamaldehyde was investigated. The CDs gave a cinnamaldehyde conversion (40%, 4 h) with selectivity towards the reduction of the C = O bond (cinnamyl alcohol) while the Pd-carbon catalyst was only selective to the reduction of the C = C bond (conversion 78%) indicating the dominance of Pd in the reaction. Post analysis of the deactivated catalysts indicated formation of carbon sheets and sintering of the Pd nanoparticles. It is thus shown that the presence of Pd induces the CDs to carbon sheet formation and thus indicates the limited use of CDs as a support for the olefin hydrogenation reaction with the CDs produced carbon support. This finding has implications for other studies using CDs as supports.Graphical abstract

Counterion Effect in Cobaltate-Catalyzed Alkene Hydrogenation.

We show that countercations exert a remarkable influence on the ability of anionic cobaltate salts to catalyze challenging alkene hydrogenations. An evaluation of the catalytic properties of [Cat][Co(η4 -cod)2 ] (Cat=K (1), Na (2), Li (3), (Dep nacnac)Mg (4), and N(n Bu)4 (5); cod=1,5-cyclooctadiene, Dep nacnac={2,6-Et2 C6 H3 NC(CH3 )}2 CH)]) demonstrated that the lithium salt 3 and magnesium salt 4 drastically outperform the other catalysts. Complex 4 was the most active catalyst, which readily promotes the hydrogenation of highly congested alkenes under mild conditions. A plausible catalytic mechanism is proposed based on density functional theory (DFT) investigations. Furthermore, combined molecular dynamics (MD) simulation and DFT studies were used to examine the turnover-limiting migratory insertion step. The results of these studies suggest an active co-catalytic role of the counterion in the hydrogenation reaction through the coordination to cobalt hydride intermediates.

Chiral 1‐Phosphabarrelene‐Pyridines as Suitable Ligands for the Rh/Ir‐Catalyzed Asymmetric Hydrogenation of Olefins

AbstractHerein, we report the synthesis of chiral phosphabarrelene‐pyridine ligands. Their synthesis benefit from modified reaction conditions to overcome the low yields normally associated with the [4+2] cycloaddition reaction of phosphinines with hexafluoro‐2‐butyne, which is a key to install the P‐stereocenter in the phosphabarrelene. Their potential as chelating ligands in asymmetric catalysis was assessed in the Rh‐ and Ir‐catalyzed hydrogenation of cyclic β‐enamides and β‐dehydroamino acid derivatives. The catalytic system containing a tert‐butyl substituent at the ortho position of the phosphabarrelene moiety successfully hydrogenates a range of cyclic β‐enamides (ee's between 92% to 94%) and β‐dehydroamino acid derivatives (ee's between 93% to 95%). Moreover, the reactions can be carried out in the environmentally friendly 1,2‐propylene carbonate as solvent with no loss of enantioselectivity. Mechanistic studies with the Rh/P,N catalytic systems agree with the Landis‐Halpern mechanism and explain the influence of the substituent at the phosphabarrelene on enantioselectivity. Finally, the hydrogenation reactions can be carried out at large scale maintaining high enantioselectivities.

Counterion Effect in Cobaltate‐Catalyzed Alkene Hydrogenation

AbstractWe show that countercations exert a remarkable influence on the ability of anionic cobaltate salts to catalyze challenging alkene hydrogenations. An evaluation of the catalytic properties of [Cat][Co(η4‐cod)2] (Cat=K (1), Na (2), Li (3), (Depnacnac)Mg (4), and N(nBu)4 (5); cod=1,5‐cyclooctadiene, Depnacnac={2,6‐Et2C6H3NC(CH3)}2CH)]) demonstrated that the lithium salt 3 and magnesium salt 4 drastically outperform the other catalysts. Complex 4 was the most active catalyst, which readily promotes the hydrogenation of highly congested alkenes under mild conditions. A plausible catalytic mechanism is proposed based on density functional theory (DFT) investigations. Furthermore, combined molecular dynamics (MD) simulation and DFT studies were used to examine the turnover‐limiting migratory insertion step. The results of these studies suggest an active co‐catalytic role of the counterion in the hydrogenation reaction through the coordination to cobalt hydride intermediates.