Rhodium-Catalyzed Arene Alkenylation: Selectivity and Reaction Mechanism as a Function of In Situ Oxidant Identity
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Rhodium-Catalyzed Arene Alkenylation Using Benzoquinone Derivatives as Oxidants
The Rh-catalyzed conversion of olefins and arenes to alkenyl arenes using [(η 2 -C 2 H 4 ) 2 Rh(μ-OPiv)] 2 as the catalyst precursor and 12 ortho- and para-substituted benzoquinone derivatives as the in situ oxidant is reported. Included are comparative studies of the quinone derivatives for (1) rate of styrene production from benzene and ethylene, (2) Markovnikov to anti-Markovnikov selectivity for reactions of benzene and propylene, and (3) ortho/meta/para selectivity when using tert-butylbenzene as the arene. Cyclic voltammetry was utilized to measure reduction potentials for each quinone to determine any possible influence of the quinone redox potential on arene alkenylation rate and selectivity. While significant differences in selectivity are observed between ortho -quinone derivatives, such differences are minimal when para-substituted quinones are utilized. These results suggest that ortho -benzoquinone derivatives likely serve as bidentate ligands, which explains the stronger influence on catalyst activity of ortho -benzoquinone identity compared to para -benzoquinones. Although ortho -benzoquinones generally give styrene production rates faster than those of para -benzoquinones, 3,5-di- tert -butyl- ortho -benzoquinone and ortho -chloranil react with ethylene to form bicyclo[2.2.2]oct-5-ene-2,3-dione derivatives as a significant side product.
aromatic compounds↗
Kinetically Controlled Synthesis of Rhodium Nanocrystals with Different Shapes and a Comparison Study of Their Thermal and Catalytic Properties
Here, we report the synthesis of Rh nanocrystals with different shapes by controlling the kinetics involved in the growth of preformed Rh cubic seeds. Specifically, Rh nanocrystals with cubic, cuboctahedral, and octahedral shapes can all be obtained from the same cubic seeds under suitable reduction kinetics for the precursor. The success of such a synthesis also relies on the use of a halide-free precursor to avoid oxidative etching, as well as the involvement of a sufficiently high temperature to remove Br – ions from the seeds while ensuring adequate surface diffusion. The availability of Rh nanocrystals with cubic and octahedral shapes allows for an evaluation of the facet dependences of their thermal and catalytic properties. The data from in situ electron microscopy studies indicate that the cubic and octahedral Rh nanocrystals can keep their original shapes up to 700 and 500 °C, respectively. When tested as catalysts for hydrazine decomposition, the octahedral nanocrystals exhibit almost 4-fold enhancement in terms of H 2 selectivity relative to the cubic counterpart. As for ethanol oxidation, the order is reversed, with the cubic nanocrystals being about three times more active than the octahedral sample.
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Heterogeneous Rhodium Single-Atom-Site Catalyst Enables Chemoselective Carbene N–H Bond Insertion
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Bottom-up evolution of perovskite clusters into high-activity rhodium nanoparticles toward alkaline hydrogen evolution
Self-reconstruction has been considered an efficient means to prepare efficient electrocatalysts in various energy transformation process for bond activation and breaking. However, developing nano-sized electrocatalysts through complete in-situ reconstruction with improved activity remains challenging. Herein, we report a bottom-up evolution route of electrochemically reducing Cs 3 Rh 2 I 9 halide-perovskite clusters on N-doped carbon to prepare ultrafine Rh nanoparticles (~2.2 nm) with large lattice spacings and grain boundaries. Various in-situ and ex-situ characterizations including electrochemical quartz crystal microbalance experiments elucidate the Cs and I extraction and Rh reduction during the electrochemical reduction. These Rh nanoparticles from Cs 3 Rh 2 I 9 clusters show significantly enhanced mass and area activity toward hydrogen evolution reaction in both alkaline and chlor-alkali electrolyte, superior to liquid-reduced Rh nanoparticles as well as bulk Cs 3 Rh 2 I 9 -derived Rh via top-down electro-reduction transformation. Theoretical calculations demonstrate water activation could be boosted on Cs 3 Rh 2 I 9 clusters-derived Rh nanoparticles enriched with multiply sites, thus smoothing alkaline hydrogen evolution.
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Integrated in situ spectroscopic studies on syngas production from partial oxidation of methane catalyzed by atomically dispersed rhodium cations on ceria
Catalytic reforming of methane to produce syngas is an important strategy for producing value-added chemicals. The conventional reforming catalyst relies on supported nickel nanoparticles. Here, in this work, we investigated singly dispersed Rh cations anchored on a CeO 2 catalyst (Rh 1 /CeO 2 ) for high activity and selectivity towards the production of syngas via partial oxidation of methane (POM) in the temperature range of 600–700 °C. The yields of H 2 and CO at 700 °C are 83% and 91%, respectively. The anchored Rh 1 atoms on CeO 2 of Rh 1 /CeO 2 are in the cationic state, and on an average each Rh 1 atom coordinates with 4–5 surface lattice oxygen atoms of CeO 2 . Compared to inert CeO 2 for POM, via the incorporation of single-atom sites, Rh 1 modifies the electronic state of oxygen atoms proximal to the Rh 1 atoms and thus triggers the catalytic activity of CeO 2 . The high activity of single-atom catalyst Rh 1 /CeO 2 suggests that the incorporation of single atoms of transition metals to the surface of a reducible oxide can modulate the electronic state of proximal anions of the oxide support toward forming an electronic state favorable for the selective formation of ideal products.
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Structure and bonding in rhodium coordination compounds: a 103 Rh solid-state NMR and relativistic DFT study
We present the rapid and robust acquisition of 103 Rh solid-state NMR spectra for a series of inorganic and organometallic compounds. Relativistic DFT calculations provide relationships between 103 Rh chemical shift tensors, structure, and bonding.
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Support modification by phosphonic acid ligands controls ethylene hydroformylation on single-atom rhodium sites
To investigate the ability of surface-bound ligands to control activity toward ethylene hydroformylation, we modified site-isolated Rh 1 /TiO 2 with a series of substituted benzyl phosphonic acids. We found that modification of the support by phosphonic acids reduced break-in times for hydroformylation by 4× and increased absolute hydroformylation activity by up to 18× compared to unmodified catalyst at 150 °C. All functionalized catalysts improved hydroformylation activity by at least 9× and improved selectivity by between 7× and 60× relative to the unmodified catalyst. Carbon monoxide probe–molecule spectroscopy indicated that the enhancements in activity among modified samples were due to changes in the local environment of the active Rh site. Specifically, the bite angle of adsorbed carbon monoxide, as determined from infrared spectra, correlated with hydroformylation activity. These findings demonstrate that Rh 1 active sites are highly sensitive to modification of the support with organic ligands.
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Effects of rhodium doping on dislocation nucleation in a [001] SrNi 2 P 2 single crystal under spherical nanoindentation
Nanoindentation was performed on SrNi 2 P 2 single crystals and their dilute solid solutions, Sr(Ni 1–x Rh x ) 2 P 2 (x = 0 ~ 0.055), under [001] loading to investigate the effects of elemental doping on Young’s modulus and dislocation nucleation stress. The results show that Young’s modulus and the dislocation nucleation stress decrease as the Rh content increases, and their Rh content dependence also varies with the Rh content. Electron diffraction analysis and the anisotropic lattice distortion calculations revealed that a local structural transition from the orthorhombic superstructure to the tetragonal structure and local compressive residual stresses could be the main reasons for the decrease in Young’s modulus and dislocation nucleation stress, respectively. The overlap of stress–strain fields between Rh atoms and the associated local structural transition contribute to their Rh content dependence. Here, the results also indicate that elemental doping does not necessarily strengthen materials if the incipient plasticity is controlled by dislocation nucleation, unlike conventional solid solution strengthening.
36 MATERIALS SCIENCE↗
Electroplated Rhodium as a Functional Adhesion Layer
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Murtagh, Christopher↗
Catalytic synthesis of super linear alkenyl arenes using rhodium catalysts
Catalytic methods for synthesis of super linear alkenyl arenes and alkyl arenes are provided. The methods are capable of synthesizing super linear alkyl and alkenyl arenes from simple arene and olefin starting materials and with high selectivity for linear coupling. Methods are also provided for making a 2,6-dimethylnapthalene (DMN) or 2,6-methylethylnapthalene (MEN).
Schinski, William↗
Catalytic Hydrogenation of a Manganese(V) Nitride to Ammonia
The catalytic hydrogenation of a metal nitride to make free ammonia using a rhodium hydride catalyst that promotes H 2 activation and hydrogen atom transfer is described. The phenylimine-substituted rhodium complex, (η 5 -C 5 Me 5 )Rh( Me PhI)H ( Me PhI = N-methyl-1-phenylethan-1-imine) exhibited higher thermal stability compared to the previously reported (η 5 -C 5 Me 5 )Rh(ppy)H (ppy = 2-phenylpyridine). DFT calculations established that the two rhodium complexes have comparable Rh–H bond dissociation free energies of 51.8 kcal mol-1 for (η 5 -C 5 Me 5 )Rh(MePhI)H and 51.1 kcal mol -1 for (η 5 -C 5 Me 5 )Rh(ppy)H. In the presence of 10 mol% of the phe-nylimine rhodium precatalyst and 4 atm of H 2 in THF, the manganese nitride, ( tBu Salen)Mn≡N underwent hydrogenation to liberate free ammonia with up to 6 total turnovers of NH 3 or 18 turnovers of H·. The phenylpyridine analogue proved inactive for ammonia synthesis under identical conditions owing to competing deleterious hydride transfer chemistry. Subsequent research showed that the use of a non-polar solvent such as benzene suppressed formation of the cationic rhodium product resulting from the hydride transfer and enabled catalytic ammonia synthesis by proton coupled electron transfer.
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Understanding the role of negative charge in the scaffold of an artificial enzyme for CO 2 hydrogenation on catalysis
Here, we have approached the construction of an artificial enzyme by employing a robust protein scaffold, lactococcal multidrug resistance regulator, LmrR, providing a structured secondary and outer coordination spheres around a molecular rhodium complex, [Rh I (P Et2 N gly P Et2 ) 2 ] - . Previously, we demonstrated a 2–3 fold increase in activity for one Rh-LmrR construct by introducing positive charge in the secondary coordination sphere. In this study, a series of variants was made through site-directed mutagenesis where the negative charge is located in the secondary sphere or outer coordination sphere, with additional variants made with increasingly negative charge in the outer coordination sphere while keeping a positive charge in the secondary sphere. Placing a negative charge in the secondary or outer coordination sphere demonstrates decreased activity by a factor of two compared to the wild-type Rh-LmrR. Interestingly, addition of positive charge in the secondary sphere, with the negatively charged outer coordination sphere restores activity. Vibrational and NMR spectroscopy suggest minimal changes to the electronic density at the rhodium center, regardless of inclusion of a negative or positive charge in the secondary sphere, suggesting another mechanism is impacting catalytic activity, explored in the discussion.
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Effects of 18 O Exchange on Neutron Emission Rates of Aging 238 PuO 2 LWRHUs
The Lightweight Radioisotope Heater Unit (LWRHU) provides about 1 Watt of thermal power to critical electrical and mechanical systems in the extreme temperatures of space, maintaining the operating temperature of the spacecraft’s scientific and general operating equipment. Los Alamos National Laboratory (LANL) designed and tested the LWRHU in the 1970s through early 1980s. The first production campaign at LANL was in the early 1980s in support of the Galileo mission in which over 100 LWRHUs were manufactured. In the mid-1990s, almost 200 LWRHUs were manufactured in support of the Cassini mission. After the primary Cassini manufacturing campaign, the Department of Energy (DOE) approved the fabrication of more than 10 additional LWRHUs as spares in 1998. The LWRHU assembly contains the following components: a fuel pellet, a vented capsule, a pyrolytic graphite insulator, and a fine-weave pierced fabric (FWPF) graphite aeroshell. The fuel pellet is a hot-pressed 238 PuO 2 cylindrical pellet that is sintered to create a ceramic pellet. The pellet is encapsulated in a platinum-rhodium encapsulation. The welded fueled clad is placed inside a pyrolytic graphite thermal insulation to protect the fuel from the heat produced in reentry events. The exterior layer of the LWRHU assembly is the FWPF aeroshell. Before sintering, PuO 2 granules are heated in a furnace at temperatures greater than or equal to 700°C under an enriched 16 O atmosphere in order to reduce trace quantities of 18 O. Because 18 O undergoes an (α,n) reaction, 18 O needs to be removed as much as possible to meet radiation emission requirements set by the Jet Propulsion Laboratory (JPL) and the National Aeronautics and Space Administration (NASA), as well as other agencies. The relative abundances of the oxygen isotopes are indicated by neutron emission rate (NER) measurements. LWRHUs are vented with a sintered platinum frit vent (George 1986). During extraterrestrial operation, the vent in the cladding allows helium from the decay of plutonium to escape and relieves pressure from the system while preventing the solids from escaping (Rinehart 1996, Tate 1982 & 1985). This vent is protected during manufacture by a platinum-30 rhodium cover. The capsule vent is activated by milling a 0.025-inch diameter hole through the protective cover to a nominal depth of 0.015 inches, generally immediately before the LWRHU is loaded into the aeroshell (George 1986). Prior to long-term storage, LWRHUs are vented and thus potentially allow infiltration of 18 O from the ambient atmosphere. Although NER decreases with age due to the reduction in emitted alpha particles, it might be expected that NER reduction is mitigated by the exchange of 18 O. However, this is not necessarily the case and no trend was observed relating NER to age other than the natural decay of 238 Pu (Mulford 2021). The most probable and dominant factor for determining specific NER was manufacturing discrepancies between individual units. It is important to understand the lack of observed 16 O- 18 O exchange and to compare LWRHU pellets as much as possible.
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
Bulk-like first-order magnetoelastic transition in FeRh particles
Near-equiatomic, chemically-ordered iron-rhodium (FeRh) alloy is a fundamentally interesting material that may become useful in niche applications making use of its unique magneto functional phenomena, for example, the giant inverse magnetocaloric effect near room temperature that is associated with a sharp first-order magnetic phase transition. The nearly discontinuous antiferromagnetic-ferromagnetic phase transformation in bulk FeRh is well-known; however, the transition broadens considerably in fine particles and films with thickness less than 50 nm, precluding their potential applications. Here, we report an abrupt, bulk-like first-order magnetoelastic transformation in powders consisting of sub-micron particles of nearly equiatomic FeRh compound synthesized via solid-state mechanochemical co-reduction of FeF 2 and RhCl3 and subsequent heat treatments. In this work, we demonstrate that annealing at temperatures ranging from 600 °C to 800 °C enables tailoring phase content, particle size, and magnetic properties of the powders. A maximum magnetic-field-induced entropy change of ~10 J/kg K at μ0ΔH = 1 T has been achieved in powders annealed at 800 °C. The retention of extraordinary responsiveness in sub-micron particles of FeRh is likely to open doors for system component fabrication using additive manufacturing methods, along with new opportunities to employ FeRh in theranostics.
36 MATERIALS SCIENCE↗