Trimethylaluminum Activates Zeolite-Confined Lanthanum Borohydrides to Enhance Catalytic C–H Borylation

Journal of the American Chemical Society, Journal Year: 2025, Volume and Issue: unknown

Published: April 3, 2025

AlMe3-treatment of the borylation precatalyst La(BH4)2(THF)2.5-Ph3Si-HY30 affords La(BH4)2(AlMe3)-Ph3Si-HY30, which is superior lanthanum-based for benzene with pinacolborane (HBpin), giving higher turnovers (>285) and improved yields (up to 42%) phenylpinacolborane (PhBpin). Solid-state NMR spectroscopy, X-ray adsorption theoretical studies characterized precatalytic sites in La(BH4)2(AlMe3)-Ph3Si-HY30 as κ2-O,O-{≡SiO(=Al)≡SiO}La(BH4)2(AlMe3), revealing that AlMe3 had displaced THF ligands. In contrast expected high reactivity THF-free organolanthanum, turnover frequency (TOF) PhBpin formation catalyzed by (2.7 h-1) slightly lower than untreated (3.6 h-1), implying a stronger inhibitor lanthanum. On other hand, inactive La(BH4)2(THF)2.2-SiO2 generates an active catalyst. also desorbs surface-O-BxHy species quenches residual Brønsted acid (BAS) silanols. Alumination BAS inhibits HBpin degradation, while alumination silanols creates reaction. The 8-fold inhibition BAS-catalyzed decomposition rate treatment gives kinetic advantage lanthanum-catalyzed C-H borylation, leading increased turnovers. Knowledge competing roles catalytic law enables identification favorable conditions low [HBpin] maximize or yield. Sterics affect selectivity substituted arenes heteroarenes, can proceed without precoordination donor. These steric effects, well having opposite effect on activity lanthanum HY vs SiO2, point confinement-activated sites.

Language: Английский

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Rapid Polyolefin Plastic Hydrogenolysis Mediated by Single-Site Heterogeneous Electrophilic/Cationic Organo-group IV Catalysts

ACS Catalysis, Journal Year: 2023, Volume and Issue: 14(1), P. 554 - 565

Published: Dec. 26, 2023

A homologous series of cationic electrophilic group IV metal hydrides (M = Ti, Zr, Hf) created by chemisorption the corresponding MNp4 precursors on highly Brønsted acidic sulfated alumina (AlS) to yield loosely coordinated surface AlS/MNp2 (Np neopentyl) species are systematically characterized ICP, EXAFS/XANES, DRIFTS, and solid-state high-resolution multidimensional NMR spectroscopy (SSNMR), as well energy span DFT computation. With effective stirring, these complexes readily undergo reaction with H2 AlS/M(alkyl)H species, which active for hydrogenolysis diverse commercial polyethylenes, α-olefin-ethylene copolymers, isotactic polypropylene, postconsumer polyolefins including high-density yielding medium small linear branched hydrocarbons at turnover frequencies high 36,300 h–1 200 °C/17 atm M Zr. For given polyolefin conditions, scale approximately Zr > Hf whereas catalyst thermal stability scales ≈ trends qualitatively understandable from analysis. These catalytic results reveal that AlS/Hf(R)H-mediated favors wax-like liquid products, AlS/Zr(R)H-mediated can be tuned between gases liquids. analysis identifies β-alkyl elimination turnover-limiting C–C scission process, is particularly facile in d0 but not so neutrally charged analogues.

Language: Английский

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A Supported Ziegler-Type Organohafnium Site Metabolizes Polypropylene

Journal of the American Chemical Society, Journal Year: 2023, Volume and Issue: unknown

Published: Nov. 3, 2023

Cp2Hf(CH3)2 reacts with silica containing strong aluminum Lewis sites to form Cp2Hf–13CH3+ paired aluminate anions. Solid-state NMR studies show that this reaction also forms neutral organohafnium and hafnium lacking methyl groups. isotatic polypropylene (iPP, Mn = 13.3 kDa; Đ 2.4; mmmm 94%; ∼110 C3H6/Hf) H2 oils moderate molecular weights (Mn 290–1200 Da) in good yields. The aliphatic characteristic 13C{1H} properties consistent complete loss of diastereoselectivity formation regioirregular errors under 1 atm H2. These results a Ziegler–Natta-type active site is compatible common used digest waste plastic into smaller fragments.

Language: Английский

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Rapid Polyolefin Hydrogenolysis by a Single‐Site Organo‐Tantalum Catalyst on a Super‐Acidic Support: Structure and Mechanism

Angewandte Chemie International Edition, Journal Year: 2023, Volume and Issue: 62(50)

Published: Nov. 10, 2023

Abstract The novel electrophilic organo‐tantalum catalyst AlS/TaNp x ( 1 ) (Np=neopentyl) is prepared by chemisorption of the alkylidene Np 3 Ta=CH t Bu onto highly Brønsted acidic sulfated alumina (AlS). proposed structure supported EXAFS, XANES, ICP, DRIFTS, elemental analysis, and SSNMR measurements in good agreement with DFT analysis. Catalyst effective for hydrogenolysis diverse linear branched hydrocarbons, ranging from C2 to polyolefins. To best our knowledge, exhibits one highest polyolefin activities (9,800 (CH 2 units) ⋅ mol(Ta) −1 h at 200 °C/17 atm H reported date peer‐reviewed literature. Unlike AlS/ZrNp analog, Ta more thermally stable offers multiple potential C−C bond activation pathways. For hydrogenolysis, a wide variety pre‐ post‐consumer plastics not significantly deactivated standard additives typical industrial concentrations.

Language: Английский

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Highly Selective and Efficient Perdeuteration of n‐Pentane via H/D Exchange Catalyzed by a Silica‐Supported Hafnium‐Iridium Bimetallic Complex

Angewandte Chemie, Journal Year: 2024, Volume and Issue: 136(16)

Published: Feb. 19, 2024

Abstract A Surface OrganoMetallic Chemistry (SOMC) approach is used to prepare a novel hafnium‐iridium catalyst immobilized on silica, HfIr/SiO 2 , featuring well‐defined [≡SiOHf(CH t Bu) (μ‐H) 3 IrCp*] surface sites. Unlike the monometallic analogous materials Hf/SiO and Ir/SiO which promote n ‐pentane deuterogenolysis through C−C bond scission, we demonstrate that under same experimental conditions (1 bar D 250 °C, h, 0.5 mol %), heterobimetallic highly efficient selective for perdeuteration of alkanes with exemplified ‐pentane, without substantial (<2 % at 95 conversion). Furthermore this robust can be re‐used several times evidence decomposition. This represents advance in catalytic H/D isotope exchange (HIE) reactions C(sp )−H bonds.

Language: Английский

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Alkene Isomerization using a Heterogeneous Nickel-Hydride Catalyst

Published: May 13, 2024

Transition metal-catalyzed alkene isomerization is an enabling technology used to install distal its original site. Due their well-defined structure, homogeneous catalysts can be fine-tuned optimize reactivity, stereoselectivity, and positional selectivity, but they often suffer from instability non-recyclability. Heterogeneous are generally highly robust continue lack active-site specificity challenging rationally improve through structural modification. Known single-site heterogeneous for utilize precious metals bespoke, expensive, synthetically intense supports. Additionally, have mediocre inspiring us develop a catalyst with active site made readily available compounds of Earth-abundant elements. Previous work demonstrated that very formed upon protonation Ni[P(OEt)3]4 by H2SO4, generating [Ni–H]+ This incredibly active, also decomposes readily, which severely limits utility. Herein we show using solid acid (sulfated zirconia, SZO300), not only this de-composition prevented, high activity maintained, improved selectivity achieved, broader scope functional groups tolerated. Preliminary mechanistic experiments suggest the catalytic reaction likely goes intermolecular, two-electron pathway. A detailed kinetic study comparing state-of-the-art Ni Pd reveals highest seen Ni/SZO300 system. The reactivity Ni/SZO300, limited isomerization; it competent hydroalkenylation, hydroboration, hydrosilylation, demonstrating broad application catalyst.

Language: Английский

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Influence of Trace Metal in Plastics on Catalyst Activity and Reusability during Polyolefins Upcycling with Polyoxometalates

ACS Catalysis, Journal Year: 2024, Volume and Issue: 14(20), P. 15633 - 15644

Published: Oct. 7, 2024

The influence of trace metals in waste plastics on catalyst activity and reusability has received scant attention the upcycling literature. Catalytic cracking high-density polyethylene (HDPE) was demonstrated over unsupported acidic W-based polyoxometalates an up-flow fixed-bed reactor using flowing nitrogen to recover cracked hydrocarbon products. product distribution depends prereduction method, temperature effluent reflux zone. For recycling catalyst, we harnessed aqueous solubility dissolve separate spent from coke. Prereducing mitigates coke formation by substrate dehydrogenation eases recovery. On a freshly H2-prereduced observe at temperatures as low 573 K. At 623 313 K respectively, ∼80% yield predominantly paraffinic hydrocarbons with average formula C21.9H45.9. We discovered that Cr traces present HDPE progressively accumulate recycled increase activity. After five recycles, accumulation ∼137 ppm shifts lower C15.1H31.9. Higher content reduces stability Keggin structure strongly reducing environment H2. In sharp contrast, olefins instead H2 can preserve structural integrity. Electron paramagnetic resonance (EPR) spectroscopy studies computational results support hypothesis both incorporation Cr, which is much harder than W introduces odd number d electrons (as either olefin or PE reduction does), well extent catalysts may affect atomic electronic structures heteropolytungstates, influencing their acidity These fundamental insights highlight challenges posed upcycling.

Language: Английский

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Alkene Isomerization using a Heterogeneous Nickel-Hydride Catalyst

Published: Sept. 21, 2023

Transition metal-catalyzed alkene isomerization is an enabling technology used to install distal its original site. Due their well-defined structure, homogeneous catalysts can be fine-tuned optimize reactivity, stereoselectivity, and positional selectivity, but they often suffer from instability non-recyclability. Heterogeneous are generally highly robust, continue lack active-site specificity challenging rationally improve through structural modification, therefore exhibiting lower catalytic performance. Known single-site heterogeneous for utilize precious metals bespoke, expensive, synthetically intense supports. Additionally, have mediocre inspiring us develop a catalyst with active site made readily available compounds of Earth-abundant elements. Previous work demonstrated that very homoge-neous formed upon protonation Ni[P(OEt)3]4 by H2SO4, generating [Ni–H]+ This in-credibly active, also decomposes readily, which severely limits utility. Herein we show using solid acid (sulfated zirconia, SZO300), not only this decomposition prevented, high activity maintained, improved selectivity achieved, broader scope functional groups tolerated. Preliminary mechanistic experiments suggest the likely goes intermolecular, two-electron pathway. A detailed kinetic study comparing state-of-the-art Ni Pd reveals highest seen Ni/SZO300 system. The reactivity Ni/SZO300, limited isomerization; it competent hydroalkenylation, hydroboration, hydrosilylation, demonstrating broad application catalyst.

Language: Английский

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Rapid Polyolefin Plastics Hydrogenolysis Mediated by Single-Site Heterogeneous Electrophilic/Cationic Organo-Group IV Catalysts

Published: July 3, 2023

: A homologous series of cationic electrophilic group IV metal hydrides (M = Ti, Zr, Hf) created by chemisorption the corresponding MNp4 precursors on highly Brønsted acidic sulfated alumina (AlS) to yield loosely coordinated surface AlS/MNp2 (Np neopentyl) species are systematically characterized ICP, EXAFS/XANES, DRIFTS, and solid-state high-resolution multi-dimensional NMR spectroscopy (SSNMR), as well energy span DFT computation. With effective stirring, these complexes readily undergo reaction with H2 AlS/M(alkyl)H which active for hydrogenolysis diverse commercial polyethylenes, α-olefin-ethylene copolymers, isotactic polypropylene, post-consumer polyolefins including high-density yielding medium small linear branched hydrocar-bons at turnover frequencies high 36,300 h-1 200 °C/17 atm M Zr. For a given polyolefin conditions, scale approximately Zr > Hf while catalyst thermal stability scales approxi-mately ≈ trends qualitatively understandable from analysis. These catalytic re-sults reveal that AlS/Hf(R)H- mediated favors wax-like liquid products AlS/Zr(R)H-mediated can be tuned between gases liquids. analysis identifies β-alkyl elimination turn-over-limiting C-C scission process, is particularly facile in d0 complexes, but not so neutrally charged analogues

Language: Английский

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Rapid Polyolefin Hydrogenolysis by a Single‐Site Organo‐Tantalum Catalyst on a Super‐Acidic Support: Structure and Mechanism

Angewandte Chemie, Journal Year: 2023, Volume and Issue: 135(50)

Published: Nov. 10, 2023

Abstract The novel electrophilic organo‐tantalum catalyst AlS/TaNp x ( 1 ) (Np=neopentyl) is prepared by chemisorption of the alkylidene Np 3 Ta=CH t Bu onto highly Brønsted acidic sulfated alumina (AlS). proposed structure supported EXAFS, XANES, ICP, DRIFTS, elemental analysis, and SSNMR measurements in good agreement with DFT analysis. Catalyst effective for hydrogenolysis diverse linear branched hydrocarbons, ranging from C2 to polyolefins. To best our knowledge, exhibits one highest polyolefin activities (9,800 (CH 2 units) ⋅ mol(Ta) −1 h at 200 °C/17 atm H reported date peer‐reviewed literature. Unlike AlS/ZrNp analog, Ta more thermally stable offers multiple potential C−C bond activation pathways. For hydrogenolysis, a wide variety pre‐ post‐consumer plastics not significantly deactivated standard additives typical industrial concentrations.

Language: Английский

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