1502-06-3Relevant articles and documents
Oxidant-free dehydrogenation of alcohols heterogeneously catalyzed by cooperation of silver clusters and acid-base sites on alumina
Shimizu, Ken-Ichi,Sugino, Kenji,Sawabe, Kyoichi,Satsuma, Atsushi
, p. 2341 - 2351 (2009)
A γ-alumina-supported silver cluster catalyst - Ag/Al 2O3-has been shown to act as an efficient heterogeneous catalyst for oxidant-free alcohol dehydrogenation to carbonyl compounds at 373 K. The catalyst shows higher activity than conventional heterogeneous catalysts based on platinum group metals (PGMs) and can be recycled. A systematic study on the influence of the particle size and oxidation state of silver species, combined with characterization by Ag K-edge XAFS (X-ray absorption fine structure) has established that silver clusters of sizes below 1 nm are responsible for the higher specific rate. The reaction mechanism has been investigated by kinetic studies (Hammett correlation, kinetic isotope effect) and by in situ FTIR (kinetic isotope effect for hydride elimination reaction from surface alkoxide species), and the following mechanism is proposed: 1) reaction between the alcohol and a basic OH group on the alumina to yield alkoxide on alumina and an adsorbed water molecule, 2) CH activation of the alkoxide species by the silver cluster to form a silver hydride species and a carbonyl compound, and 3) H2 desorption promoted by an acid site in the alumina. The proposed mechanism provides fundamental reasons for the higher activities of silver clusters on acid-base bifunctional support (Al 2O3) than on basic (MgO and CeO2) and acidic to neutral (SiO2) ones. This example demonstrates that catalysts analogous to those based on of platinum group metals can be designed with use of a less expensive d10 element - silver - through optimization of metal particle size and the acid-base natures of inorganic supports.
Garbisch jun.,Wohllebe
, p. 2157 (1968)
1-Alkenylcycloalkoxy Radical Chemistry. A Two-Carbon Ring Expansion Methodology
Galatsis, Paul,Millan, Scott D.,Faber, Tim
, p. 1215 - 1220 (1993)
The exploitation of alkoxy radicals derived from 1-ethenylcycloalkanols for use in a two-carbon ring expansion protocol was proposed.Direct one-pot alkoxy radical-mediated fragmentation-cyclization was not feasible since the reactive intermediate was quenched by iodine in the reaction mixture.However, via the use of iodo epoxides 3, the tandem fragmentation-cyclization sequence could be accomplished.This afforded ring-expanded products via an endo mode of cyclization, although in one example product from an exo mode of cyclization was also isolated.This methodologywas shown to be valid for large ring compounds as well.The intermediary of iodo epoxides 3 also afforded improved yields as compared to the direct cyclization of iodo enones 4.These results are the first examples of radical cyclization to medium-sized carbocycles.
Prelog et al.
, p. 1095,1107 (1955)
Complementary and selective oxidation of hydrocarbon derivatives by two cytochrome P450 enzymes of the same family
Sarkar, Md. Raihan,Bell, Stephen G.
, p. 5983 - 5995 (2020/10/08)
The cytochrome P450 enzymes CYP101B1 and CYP101C1, which are from the bacterium Novosphingobium aromaticivorans DSM12444, can hydroxylate norisoprenoids with high activity and selectivity. With the goal of expanding and establishing their substrate range with a view to developing applications, the oxidation of a selection of cyclic alkanes, ketones and alcohols was investigated. Cycloalkanes were oxidised, but both enzymes displayed moderate binding affinity and low levels of productive activity. We improved the binding and activity of these substrates with CYP101B1 by making the active site more hydrophobic by switching a histidine residue to a phenylalanine (H85F). The presence of a ketone moiety in the cycloalkane skeleton significantly improved the oxidation activity with both enzymes. CYP101C1 preferably catalysed the oxidation of cycloalkanones at the C-2 position whereas CYP101B1 oxidised these substrates with higher productivity and at positions remote from the carbonyl group. This demonstrates that the binding orientation of the cyclic ketones in the active site of each enzyme must be different. Linear ketones were also oxidised by both enzymes but with lower activity and selectivity. Cyclic substrates with an ester directing group were more efficiently oxidised by CYP101B1 than CYP101C1. Both enzymes catalysed oxidation of these esters with high regioselectively on the ring system remote from the ester directing group. CYP101C1 selectively oxidised certain terpenoid ester substrates, such as α-terpinyl and citronellyl acetate more effectively than CYP101B1. Overall, we establish that the high selectivity and activity of these enzymes could provide new biocatalytic routes to important fine chemicals.
Ruthenium Trichloride Catalyst in Water: Ru Colloids versus Ru Dimer Characterization Investigations
Lebedeva, Anastasia,Albuquerque, Brunno L.,Domingos, Josiel B.,Lamonier, Jean-Fran?ois,Giraudon, Jean-Marc,Lecante, Pierre,Denicourt-Nowicki, Audrey,Roucoux, Alain
, p. 4141 - 4151 (2019/03/26)
An easy-to-prepare ruthenium catalyst obtained from ruthenium(III) trichloride in water demonstrates efficient performances in the oxidation of several cycloalkanes with high selectivity toward the ketone. In this work, several physicochemical techniques were used to demonstrate the real nature of the ruthenium salt still unknown in water and to define the active species for this Csp3-H bond functionalization. From transmission electron microscopy analyses corroborated by SAXS analyses, spherical nanoobjects were observed with an average diameter of 1.75 nm, thus being in favor of the formation of reduced species. However, further investigations, based on X-ray scattering and absorption analyses, showed no evidence of the presence of a metallic Ru-Ru bond, proof of zerovalent nanoparticles, but the existence of Ru-O and Ru-Cl bonds, and thus the formation of a water-soluble complex. The EXAFS (extended X-ray absorption fine structure) spectra revealed the presence of an oxygen-bridged diruthenium complex [Ru(OH)xCl3-x]2(μ-O) with a high oxidation state in agreement with catalytic results. This study constitutes a significant advance to determine the true nature of the RuCl3·3H2O salt in water and proves once again the invasive nature of the electron beam in microscopy experiments, routinely used in nanochemistry.
Cp? versus Bis-carbonyl iridium precursors as CH oxidation precatalysts
Huang, Daria L.,Vinyard, David J.,Blakemore, James D.,Hashmi, Sara M.,Crabtree, Robert H.
, p. 199 - 206 (2017/11/27)
We previously reported a dimeric IrIV-oxo species as the active water oxidation catalyst formed from a Cp?Ir(pyalc)Cl {pyalc = 2-(2′-pyridyl)-2-propanoate} precursor, where the Cp? is lost to oxidative degradation during catalyst activation; this system can also oxidize unactivated CH bonds. We now show that the same Cp?Ir(pyalc)Cl precursor leads to two distinct active catalysts for CH oxidation. In the presence of external CH substrate, the Cp? remains ligated to the Ir center during catalysis; the active species-likely a highvalent Cp?Ir(pyalc) species-will oxidize the substrate instead of its own Cp?. If there is no external CH substrate in the reaction mixture, the Cp? will be oxidized and lost, and the active species is then an iridium-μ-oxo dimer. Additionally, the recently reported Ir(CO)2(pyalc) water oxidation precatalyst is now found to be an efficient, stereoretentive CH oxidation precursor. We compare the reactivity of Ir(CO)2(pyalc) and Cp?Ir(pyalc)Cl precursors and show that both can lose their placeholder ligands, CO or Cp?, to form substantially similar dimeric IrIV-oxo catalyst resting states. The more efficient activation of the bis-carbonyl precursor makes it less inhibited by obligatory byproducts formed from Cp? degradation, and therefore the dicarbonyl is our preferred precatalyst for oxidation catalysis.