Alternative selective oxidation pathways for aldehyde oxidation and alkene epoxidation on a SiO2-supported Ru-monomer complex catalyst

Cu-catalyzed oxygenation of alkene-tethered amides with O2 via unactivated C[double bond, length as m-dash]C bond cleavage: a direct approach to cyclic imides

An efficient aerobic unactivated C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C bond cleavage process was achieved, in which the succinimide or glutarimide derivatives could be prepared directly from alkenyl amides.

The transformations of unactivated alkenes through C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C bond double cleavage are always attractive but very challenging. We report herein a chemoselective approach to valuable cyclic imides by a novel Cu-catalyzed geminal amino-oxygenation of unactivated C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C bonds. O₂ was successfully employed as the oxidant as well as the O-source and was incorporated into alkenyl amides via C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C bond cleavage for the efficient preparation of succinimide or glutarimide derivatives. Moreover, the present strategy under simple conditions can be used in the late-stage modification of biologically active compounds and the synthesis of pharmaceuticals, which demonstrated the potential application.

Extremely low loading of Ru species on hydroxyapatite as an effective heterogeneous catalyst for olefin epoxidation

An extremely low percentage of Ru species supported on hydroxyapatite exhibited high activity, excellent selectivity and good recyclability for the epoxidation of various olefins.

Cobalt immobilized on hydroxyapatite as a low-cost and highly effective heterogeneous catalyst for alkenes epoxidation under mild conditions

Transition metal Co immobilized on hydroxyapatite with a loading of 0.05 wt% (denoted 0.05 wt% Co/HAP) could catalyze partial oxidation of cyclic alkenes, aromatic alkenes and aliphatic alkenes to yield epoxide products with excellent selectivity at 30 °C with O₂ and iso-butyraldehyde as co-oxidant. The TOF value was as high as 6261 h⁻¹ for epoxidation of cyclohexene. In addition, the prepared 0.05 wt% Co/HAP catalyst can be re-used at least 6 times without significant loss of catalytic activity and selectivity.

Transition metal Co immobilized on hydroxyapatite even with low loading of 0.05 wt% is a low-cost and highly effective heterogeneous catalyst for alkenes epoxidation at 30 °C with O₂ and iso-butyraldehyde as co-oxidant.

Chemoselective epoxidation of cholesterol derivatives on a surface-designed molecularly imprinted Ru–porphyrin catalyst

High chemoselectivity for the C₅C₆ epoxidation of cholesterol derivatives without protecting other oxidizable functional groups was achieved on a newly designed molecularly imprinted Ru–porphyrin catalyst using a SiO₂-support.

Preparation and catalytic performance of a molecularly imprinted Pd complex catalyst for Suzuki cross-coupling reactions

A molecularly imprinted Pd complex catalyst was successfully designed and prepared on a SiO₂ surface for shape-selective Suzuki cross-coupling reaction.

Synthesis, structural characterization and catalysis of ruthenium(ii) complexes based on 2,5-bis(2'-pyridyl)pyrrole ligand

Treatment of the 2,5-bis(2'-pyridyl)pyrrolato (PDP^-) anion with {Ru(COD)Cl₂}_n in THF readily yielded [Ru(PDP)(COD)Cl] (1) in almost quantitative yield. Anion metathesis of 1 in organic solvent by NO₃^- and OTf^- (OTf^- = triflato) gave [Ru(PDP)(COD)(NO₃)] (2) and [Ru(PDP)(COD)(OTf)] (3), and in aqueous solution by BF₄^- and PF₆^- afforded aqueous complexes [Ru(PDP)(COD)(H₂O)](BF₄) (4+·BF₄^-) and [Ru(PDP)(COD)(H₂O)](PF₆) (4+·PF₆^-), respectively. Treatment of 1 with PhICl₂ in CH₂Cl₂ afforded 5 with halogenated pyrrole. These complexes exhibit similar structure, including one Ru(ii) atom, one 2,5-bis(2'-pyridyl)pyrrole and one monodentate anion or aqua ligand. Each Ru(ii) tightly binds to three adjacent coplanar sites of PDP^- ligand to form a meridional configuration. Complex 1 with NaIO₄ as the oxidant in EtOAc-CH₃CN-H₂O (ratio = 3 : 1 : 2) proved to be highly effective in the catalytic oxidation of olefins to carbonyl products.

Direct Synthesis and Catalytic Application of Ordered Mesoporous Ru/C Composites with Homogeneously Dispersed Ruthenium Nanoclusters

Direct synthesis of metal/carbon nanocomposites with ordered mesoporous frameworks has attracted increasing interest in various applications including catalysis, optics, and electronics. Herein, we demonstrate a simple one-pot co-assembly route to synthesize Ru/carbon composites by using resol, ruthenium chloride, and Pluronic F127 as a template with the assistance of 8-hydroxyquinoline. 8-Hydroxyquinoline exerts a significant influence on the mesostructure ordering and specific surface area of the Ru/carbon composites. The obtained Ru/carbon materials show well-ordered hexagonal arrays of mesopores with homogeneously dispersed sub-2 nm Ru nanoclusters throughout the carbon frameworks, which can efficiently and quantitatively hydrogenated nitrobenzene to aniline with H₂ in the absence of solvent for multiple recycling runs without loss of activity.

Iridium and rhodium “PNP” aminodiphosphine complexes used as catalysts in the oxidation of styrene

New Ir and Rh “PNP” aminodiphosphine complexes are effective catalysts in styrene oxidation withtert-butyl hydroperoxide as the oxidant. The Ir catalysts were more active than the Rh catalysts with high yields to benzaldehyde in comparison to styrene oxide.

Lewis acid catalysis and Green oxidations: sequential tandem oxidation processes induced by Mn-hyperaccumulating plants

Among the phytotechnologies used for the reclamation of degraded mining sites, phytoextraction aims to diminish the concentration of polluting elements in contaminated soils. However, the biomass resulting from the phytoextraction processes (highly enriched in polluting elements) is too often considered as a problematic waste. The manganese-enriched biomass derived from native Mn-hyperaccumulating plants of New Caledonia was presented here as a valuable source of metallic elements of high interest in chemical catalysis. The preparation of the catalyst Eco-Mn1 and reagent Eco-Mn2 derived from Grevillea exul exul and Grevillea exul rubiginosa was investigated. Their unusual polymetallic compositions allowed to explore new reactivity of low oxidative state of manganese-Mn(II) for Eco-Mn1 and Mn(IV) for Eco-Mn2. Eco-Mn1 was used as a Lewis acid to catalyze the acetalization/elimination of aldehydes into enol ethers with high yields; a new green and stereoselective synthesis of (-)-isopulegol via the carbonyl-ene cyclization of (+)-citronellal was also performed with Eco-Mn1. Eco-Mn2 was used as a mild oxidative reagent and controlled the oxidation of aliphatic alcohols into aldehydes with quantitative yields. Oxidative cleavage was interestingly noticed when Eco-Mn2 was used in the presence of a polyol. Eco-Mn2 allowed direct oxidative iodination of ketones without using iodine, which is strongly discouraged by new environmental legislations. Finally, the combination of the properties in the Eco-Mn catalysts and reagents gave them an unprecedented potential to perform sequential tandem oxidation processes through new green syntheses of p-cymene from (-)-isopulegol and (+)-citronellal; and a new green synthesis of functionalized pyridines by in situ oxidation of 1,4-dihydropyridines.

Surface-assisted transfer hydrogenation catalysis on a γ-Al2O3-supported Ir dimer

A novel oxide-supported Ir dimer, which was found to be active for transfer hydrogenation of aromatic ketones, was prepared on a γ-Al(2)O(3) surface from an Ir dimer complex [Ir(2){η(5)-C(5)(CH(3))(5)}(2)(μ-CH(2))(2)] (Ir(2)) with an Ir=Ir bond. Detailed characterization of the γ-Al(2)O(3)-supported Ir dimer (Ir(2)/γ-Al(2)O(3)) revealed that the structure of Ir(2) consisted of an Ir dimer with an Ir-Ir bond attached to the γ-Al(2)O(3) surface by two bridged Ir-(OAl)(2)-Ir bonds. The supported Ir(2)/γ-Al(2)O(3) dimer with bridged Ir-(OAl)(2)-Ir bonds acted as an efficient catalyst for transfer hydrogenation (turnover number of acetophenone = 699 (24 h)), while homogeneous Ir(2), SiO(2)- and MgO-supported Ir(2) were much less active. A structural transformation at the interface of the Ir dimer and the γ-Al(2)O(3) surface was suggested to assist the transfer hydrogenation catalysis via the formation of an Ir(2)-H(2) species on the γ-Al(2)O(3) surface (Ir(2)-H(2)/γ-Al(2)O(3)) as a key intermediate in the transfer hydrogenation. The present study deepened the understanding of the role and dynamic behaviour of the oxide surface in the hydrogen transfer catalysis on the supported Ir dimer.

Ligand-based molecular recognition and dioxygen splitting: an endo epoxide ending

The phosphido complex RuCp*(PPh2CH=CHPPh2)(PPh2) (1) was exposed to a number of small molecules and was found to recognize and activate molecular oxygen in an unprecedented fashion: the ruthenium species split O2 in a ligand-based 4-electron reduction to produce an endo epoxide, as well as a phosphinito ligand. Based on XRD data, VT NMR studies, cyclooctene trapping studies, and crossover experiments it was determined that the reaction proceeded through an intramolecular mechanism in which initial oxidation of the phosphido ligand generated an end-on peroxo intermediate. This mechanism was also supported by computational studies and electrochemical experiments. In contrast, an analogue of 1, RuCp*(Ph2P(ortho-C6H4)PPh2)(PPh2) (3), reacted in an intermolecular fashion to generate two phosphinito ligands.

Polymer-supported catalysts for clean preparation of n-butanol

Embedding of alloy particles into a polymer surface ensures both firm supporting and easy activation.

Molecularly imprinted Ru complex catalysts integrated on oxide surfaces

Selective catalysis is critical for the development of green chemical processes, and natural enzymes that possess specialized three-dimensional reaction pockets with catalytically active sites represent the most sophisticated systems for selective catalysis. A reaction space in an enzyme consists of an active metal center, functional groups for molecular recognition (such as amino acids), and a surrounding protein matrix to prepare the reaction pocket. The artificial design of such an integrated catalytic unit in a non-enzymatic system remains challenging. Molecular imprinting of a supported metal complex provides a promising approach for shape-selective catalysis. In this process, an imprinted cavity with a shape matched to a template molecule is created in a polymer matrix with a catalytically active metal site. In this Account, we review our studies on molecularly imprinted metal complex catalysts, focusing on Ru complexes, on oxide surfaces for shape-selective catalysis. Oxide surface-attached transition metal complex catalysts not only improve thermal stability and catalyst dispersion but also provide unique catalytic performance not observed in homogeneous precursors. We designed molecularly imprinted Ru complexes by using surface-attached Ru complexes with template ligands and inorganic/organic surface matrix overlayers to control the chemical environment around the active metal complex catalysts on oxide surfaces. We prepared the designed, molecularly imprinted Ru complexes on SiO(2) surfaces in a step-by-step manner and characterized them with solid-state (SS) NMR, diffuse-reflectance (DR) UV-vis, X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller isotherm (BET), X-ray fluorescence (XRF), and Ru K-edge extended X-ray absorption fine structure (EXAFS). The catalytic performances of these Ru complexes suggest that this process of molecular imprinting facilitates the artificial integration of catalytic functions at surfaces. Further advances such as the imprinting of a transition state structure or the addition of multiple binding sites could lead to systems that can achieve 100% selective catalysis.

Surface structural-chemical characterization of a single-site d0 heterogeneous arene hydrogenation catalyst having 100% active sites

Structural characterization of the catalytically significant sites on solid catalyst surfaces is frequently tenuous because their fraction, among all sites, typically is quite low. Here we report the combined application of solid-state (13)C-cross-polarization magic angle spinning nuclear magnetic resonance ((13)C-CPMAS-NMR) spectroscopy, density functional theory (DFT), and Zr X-ray absorption spectroscopy (XAS) to characterize the adsorption products and surface chemistry of the precatalysts (η(5)-C(5)H(5))(2)ZrR(2) (R = H, CH(3)) and [η(5)-C(5)(CH(3))(5)]Zr(CH(3))(3) adsorbed on Brønsted superacidic sulfated alumina (AlS). The latter complex is exceptionally active for benzene hydrogenation, with ~100% of the Zr sites catalytically significant as determined by kinetic poisoning experiments. The (13)C-CPMAS-NMR, DFT, and XAS data indicate formation of organozirconium cations having a largely electrostatic [η(5)-C(5)(CH(3))(5)]Zr(CH(3))(2)(+)· · · AlS(-) interaction with greatly elongated Zr · · · O(AlS) distances of ~2.35(2) Å. The catalytic benzene hydrogenation cycle is stepwise understandable by DFT, and proceeds via turnover-limiting H(2) delivery to surface [η(5)-C(5)(CH(3))(5)]ZrH(2)(benzene)(+)· · · AlS(-) species, observable by solid-state NMR and XAS.