Photocatalytic Isomerization of 1-Butene over Palladium-Loaded Titanium(IV) Oxide Particles: Lewis Acid-like Features of the Photocatalyst

Solid-State Molecular Organometallic Catalysis in Gas/Solid Flow (Flow-SMOM) as Demonstrated by Efficient Room Temperature and Pressure 1-Butene Isomerization

The use of solid–state molecular organometallic chemistry (SMOM–chem) to promote the efficient double bond isomerization of 1-butene to 2-butenes under flow–reactor conditions is reported. Single crystalline catalysts based upon the σ-alkane complexes [Rh(R₂PCH₂CH₂PR₂)(η²η²-NBA)][BAr^F₄] (R = Cy, ^tBu; NBA = norbornane; Ar^F = 3,5-(CF₃)₂C₆H₃) are prepared by hydrogenation of a norbornadiene precursor. For the ^tBu-substituted system this results in the loss of long-range order, which can be re-established by addition of 1-butene to the material to form a mixture of [Rh(^tBu₂PCH₂CH₂P^tBu₂)(cis-2-butene)][BAr^F₄] and [Rh(^tBu₂PCH₂CH₂P^tBu₂)(1-butene)][BAr^F₄], in an order/disorder/order phase change. Deployment under flow-reactor conditions results in very different on-stream stabilities. With R = Cy rapid deactivation (3 h) to the butadiene complex occurs, [Rh(Cy₂PCH₂CH₂PCy₂)(butadiene)][BAr^F₄], which can be reactivated by simple addition of H₂. While the equivalent butadiene complex does not form with R = ^tBu at 298 K and on-stream conversion is retained up to 90 h, deactivation is suggested to occur via loss of crystallinity of the SMOM catalyst. Both systems operate under the industrially relevant conditions of an isobutene co-feed. cis:trans selectivites for 2-butene are biased in favor of cis for the ^tBu system and are more leveled for Cy.

Photocatalytic Transfer Hydrogenolysis of Allylic Alcohols on Pd/TiO2 : A Shortcut to (S)-(+)-Lavandulol

We report herein a regio- and stereoselective photocatalytic hydrogenolysis of allylic alcohols to form unsaturated hydrocarbons employing a palladium(II)-loaded titanium oxide; the reaction proceeds at room temperature under light irradiation without stoichiometric generation of salt wastes. Olefin and saturated alcohol moieties tolerated the reaction conditions. Hydrogen atoms were selectively incorporated into less sterically congested carbons of the allylic functionalities. This protocol allowed a short-step synthesis of (S)-(+)-lavandulol from (R)-(-)-carvone by avoiding otherwise necessary protection/deprotection steps.

Solid-state molecular organometallic chemistry. Single-crystal to single-crystal reactivity and catalysis with light hydrocarbon substrates

Solid-state molecular organometallic catalysis (SMOM-cat): synthetic routes, unique structural motifs, mobility in the solid-state and very active gas/solid isomerization catalysts.

Single-crystal to single-crystal solid/gas reactivity and catalysis starting from the precursor sigma-alkane complex [Rh(Cy₂PCH₂CH₂PCy₂)(η²η²-NBA)][BAr^F₄] (NBA = norbornane; Ar^F = 3,5-(CF₃)₂C₆H₃) is reported. By adding ethene, propene and 1-butene to this precursor in solid/gas reactions the resulting alkene complexes [Rh(Cy₂PCH₂CH₂PCy₂)(alkene)_x][BAr^F₄] are formed. The ethene (x = 2) complex, [Rh(Cy₂PCH₂CH₂PCy₂)(ethene)₂][BAr^F₄]-Oct, has been characterized in the solid-state (single-crystal X-ray diffraction) and by solution and solid-state NMR spectroscopy. Rapid, low temperature recrystallization using solution methods results in a different crystalline modification, [Rh(Cy₂PCH₂CH₂PCy₂)(ethene)₂][BAr^F₄]-Hex, that has a hexagonal microporous structure (P6₃22). The propene complex (x = 1) [Rh(Cy₂PCH₂CH₂PCy₂)(propene)][BAr^F₄] is characterized as having a π-bound alkene with a supporting γ-agostic Rh···H₃C interaction at low temperature by single-crystal X-ray diffraction, variable temperature solution and solid-state NMR spectroscopy, as well as periodic density functional theory (DFT) calculations. A fluxional process occurs in both the solid-state and solution that is proposed to proceed via a tautomeric allyl-hydride. Gas/solid catalytic isomerization of d₃-propene, H₂C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> CHCD₃, using [Rh(Cy₂PCH₂CH₂PCy₂)(η²η²-NBA)][BAr^F₄] scrambles the D-label into all possible positions of the propene, as shown by isotopic perturbation of equilibrium measurements for the agostic interaction. Periodic DFT calculations show a low barrier to H/D exchange (10.9 kcal mol^–1, PBE-D3 level), and GIPAW chemical shift calculations guide the assignment of the experimental data. When synthesized using solution routes a bis-propene complex, [Rh(Cy₂PCH₂CH₂PCy₂)(propene)₂][BAr^F₄], is formed. [Rh(Cy₂PCH₂CH₂PCy₂)(butene)][BAr^F₄] (x = 1) is characterized as having 2-butene bound as the cis-isomer and a single Rh···H₃C agostic interaction. In the solid-state two low-energy fluxional processes are proposed. The first is a simple libration of the 2-butene that exchanges the agostic interaction, and the second is a butene isomerization process that proceeds via an allyl-hydride intermediate with a low computed barrier of 14.5 kcal mol^–1. [Rh(Cy₂PCH₂CH₂PCy₂)(η²η²-NBA)][BAr^F₄] and the polymorphs of [Rh(Cy₂PCH₂CH₂PCy₂)(ethene)₂][BAr^F₄] are shown to be effective in solid-state molecular organometallic catalysis (SMOM-Cat) for the isomerization of 1-butene to a mixture of cis- and trans-2-butene at 298 K and 1 atm, and studies suggest that catalysis is likely dominated by surface-active species. [Rh(Cy₂PCH₂CH₂PCy₂)(η²η²-NBA)][BAr^F₄] is also shown to catalyze the transfer dehydrogenation of butane to 2-butene at 298 K using ethene as the sacrificial acceptor.

Double-active site synergistic catalysis in Ru–TiO2 toward benzene hydrogenation to cyclohexene with largely enhanced selectivity

A novel Ru/TiO₂ catalyst encapsulated by a porous TiO₂ coating was prepared, which exhibits a surprisingly high selectivity toward benzene hydrogenation.

Titanate nanotube-promoted chemical fixation of carbon dioxide to cyclic carbonate: a combined experimental and computational study

Titanate nanotubes are efficiently used as air- and water-tolerant, and recyclable Lewis acid catalysts for CO₂ fixation to cyclic carbonate.

Enhanced photocatalytic activities of visible-light driven green synthesis in water and environmental remediation on Au/Bi2WO6 hybrid nanostructures

Deposition of Au NPs enhances photocatalytic activity toward selective oxidation of alcohol in water and Cr(vi) reduction over Bi₂WO₆ nanosheets.