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Labilized Ligands Under Ultra-Confinement: A Solid-State 2H NMR Investigation of Ln(BH4)2(THF)2/HY30

Variable-temperature 2H NMR reveals that the THF ligands are highly labile in Ln(BH4)2(THF)2/HY30, undergoing exchange between Ln sites under confinement via low-coordinate intermediates. Potency in c...

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Group 4 Metallocenes Supported on Sulfated Zirconium Oxide Catalyze Benzene C–H Borylation

C–H bond functionalization of arenes with boranes continues to be a challenge in catalysis, with late transition and rare earth metals shown to be catalytically active. In this study, group 4 metallocenes grafted onto acidic sulfated zirconia (SZO) are demonstrated to catalyze arene borylation with pinacolborane (HBpin). Catalysis studies at partial HBpin conversions (59–68%) using Cp2M(Me)/SZO (M = Ti, Zr, or Hf; Cp = cyclopentadienyl) catalysts reveal that Zr exhibits greater selectivity and activity than Ti and Hf. At 0.16 mol % of Zr, Cp2ZrMe/SZO achieves 332 turnovers at high HBpin conversion (86%), making this catalyst comparably active to previously reported Ir and Rh C–H borylation catalysts. At 160 °C, a maximum chemoselectivity of 82% for PhBpin was observed at 24% HBpin conversion. The superior activity of ionic Cp2ZrMe/SZO compared to neutral Cp2ZrMe/SiO2 demonstrates the borylation mechanism relies on the highly electrophilic, coordinatively unsaturated cationic sites stabilized by the weakly coordinating sulfated support. Furthermore, both catalysts significantly outperform their molecular analogues, Cp2ZrMe2 and [Cp2ZrMe][B(C6F5)4], suggesting that the support enhances catalytic performance by stabilizing the active species.

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Regioselective Hydrosilylation Catalysis with Supported Well-Defined Pt(0) Complexes: Effects of Surface Anions and Phosphenium Ligands

Achieving stable, selective single-atom catalysts is challenging because localsurface-site structures are difficult to control. Surface organometallic chemistry and organic–inorganic hybrid materials ...

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Postdoctoral Research Associate - Ames National Laboratory

Position Title: Postdoctoral Research Associate - Ames National Laboratory Appointment Type: Post Doc/Trainee Job Description: Summary of Duties and Responsibilities: As a U. S. Department of Energy (...

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Biomolecular NMR Facility Manager

Position Title: Biomolecular NMR Facility Manager Job Group: Professional & Scientific Required Minimum Qualifications: Bachelor’s degree and 5 years of related experience Preferred Qualifications...

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DFT calculations and theory do not support enantiospecificity in NMR J-coupling constants - Nature Communications

Nature Communications - DFT calculations and theory do not support enantiospecificity in NMR J-coupling constants

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Falcon Space - Advanced Propulsion Research & Development

Falcon Space is working to make the dream of advanced propulsion a reality through innovative experiments and UAP Reverse-Engineering.

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Boron Monoxide is a One-Dimensional Polymer

It was recently reported that boron monoxide (BO) is formed through the cross-linking of B4O2 structural building units. Multiple theoretical phases agree with this description. Using pycnometry, mult...

doi.org

Determining the Conformation of Supported Complexes Using an 17O TEDOR-like NMR Experiment

Dynamic nuclear polarization surface-enhanced nuclear magnetic resonance (NMR) spectroscopy has enabled the determination of the three-dimensional configuration of surface sites, in particular supported metal complexes of relevance to single-site heterogeneous catalysis. These approaches have chiefly leveraged the application of NMR double-resonance experiments that either reveal the complex conformation via point-to-point intramolecular distances between spin-labeled atoms or the complex-surface orientation via distances between the spins and the surface plane. Either method typically requires expensive isotope labeling and each reports on different structural features. The application of an experiment that simultaneously reveals both types of distances with chemical resolution would be ideal. In this article, we describe an 17O{1H} pseudo-3D correlation experiment that achieves this goal. Specifically, Si–O–Si and Si–O–M oxygens are well-resolved by 17O NMR; therefore, distances can be simultaneously measured radially, between Si–17O–M and the 1H’s of the ligands, and vertically to the Si–17O–Si linkages of the silica support. We demonstrate the experiment using supported yttrium and zirconium complexes. Good agreement is obtained when comparing the experimental results to theoretical predictions from density functional theory calculations, highlighting the reliability of this relatively simple experiment.

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Synthesis and Properties of Poly(vinyl chloride)-b-polyethylene Multiblock Copolymers through the Hydrodechlorination of PVC with Silylium Ions

Block copolymers of polyethylene (PE) and polyvinyl chloride (PVC) have remained elusive materials despite PE and PVC being the first and third most produced polymers globally, respectfully. The closest material is chlorinated polyethylene (CPE), which is commonly used as a compatibilizer and is synthesized by functionalizing PE. However, there does not exist a synthetic pathway either from monomers or via the functionalization of PE to yield a polymer that has a controlled chlorine amount and primary structure along the polymer chain. Herein, we report a series of novel block copolymers of PVC and PE, synthesized through selective hydrodechlorination of PVC. Contrary to CPE, the full range of chlorination can be obtained, and the block number can be altered. Interfacial adhesion studies reveal samples with competitive compatibilization of PVC/polyolefin elastomer (POE) blends. This method shows that postpolymerization modification can be a strategic top-down synthesis to achieve high-performance polymers that cannot be synthesized via conventional polymerization pathways.

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Surface Protected Organozirconium Catalyzes C–H Alumination of Saturated Hydrocarbons

Surface grafted organozirconium-catalyzes C–H/Et–Al exchange reactions, involving saturated hydrocarbons and AlEt3, to afford organoaluminum compounds and ethane. The Zr(OtBu)3@SiO2-Al2O3-700 (1) cat....

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Ultra-Confined Environments May Restrict the Possible Configurations of Supported Metal Complexes

The rotation frequencies of amido ligands are highly sensitive to the electronic structure of d0 transition metal complexes and have been used to study ligand donor properties. While attempting to study the donor properties of silanolate ligands in a silica-supported Cr complex, we observed highly restricted motions due to the added steric hindrance from the support, with only approximately half of the amides rotating on a 50 ms time scale. Surprisingly, when the same species is grafted into narrow 2.2 nm pores, all amido ligands are able to rotate. Density functional theory calculations suggest that confinement may limit the possible coordination sites and the configuration of the formed surface species, potentially enabling the formation of conformationally homogeneous surface site populations.

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Research Associate in Chemistry

The Department of Chemistry at the University of Virginia (UVA) invites applications for a Postdoctoral Research Associate to work in the laboratory of Prof. Amrit Venkatesh. The postdoc will engage i...

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Well-defined Pt(0) heterogeneous hydrosilylation catalysts supported by a surface bound phosphenium

Single atom, low valent transition metals are important for heterogeneous catalysis but are challenging to generate and stabilize in a well-defined manner. Herein, we explored the functionalization of...

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Perspectives on the Dynamic Nuclear Polarization Mechanisms of Monoradicals: Overhauser Effect or Thermal Mixing?

This mini-review summarizes the evolving debate regarding the origins of the absorptive features seen in the dynamic nuclear polarization (DNP) spectra of certain monoradicals when they are irradiated at their electron Larmor frequency. This feature has drawn attention due to its reverse scaling with respect to the magnetic field strength and potential for high-field DNP. Two competing hypotheses have been introduced to explain the DNP feature based on (1) the Overhauser effect and low-temperature molecular dynamics and (2) radical clustering and a thermal mixing mechanism. Since the original discovery, a large number of experimental observations have been made in attempts to understand and ultimately leverage the mechanism. We summarize these observations and provide critical assessments of how the competing hypotheses approach them.

pubs.acs.org

Postdoctoral Research Associate - Ames National Laboratory

Position Title: Postdoctoral Research Associate - Ames National Laboratory Appointment Type: Post Doc/Trainee Job Description: Summary of Duties and Responsibilities: Would you like to work for a Nati...

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