Effect of Carboxylate Ligands on Alkane Dehydrogenation with (dmPhebox)Ir Complexes

Hongmei Yuan, William W. Brennessel , and William D. Jones* 

Department of Chemistry, University of Rochester, Rochester, New York 14627, United States

ACS Catal., 2018, 8, pp 2326–2329

DOI: 10.1021/acscatal.7b04057

A series of carboxylate-ligated iridium complexes (dmPhebox)Ir(O2CR)2(H2O) (R = −CH3, −CH2CH3, −CMe3, −CH2C6H5, and −CH═CMe2) were designed and synthesized to understand the carboxylate ligand effects on the reactivity of the complex for alkane dehydrogenation. Kinetic studies showed that the different R groups of the carboxylate iridium complexes can affect the reactivity with octane in the β-H elimination step. The rate constants for octene formation with different carboxylate ligands follow the order R = −CH═CMe2 > −CMe3 > −CH2CH3 > −CH3 > −CH2C6H5. In contrast, there is no significant effect of carboxylate ligand on the rate of the C–H activation step at 160 °C. These experimental results support the findings in the previously reported density functional theory study of the (dmPhebox)Ir complex in alkane C–H activation.

Keywords: 

concerted-metalation−deprotonation; C−H activation; dehydrogenation; iridium; kinetics

Hydrogen/Deuterium (H/D) Exchange Catalysis in Alkanes

https://pubs.acs.org/doi/10.1021/acscatal.7b04201

Aaron Sattler*
Corporate Strategic Research, ExxonMobil Research & Engineering Company, 1545 Route 22 East, Annandale, New Jersey 08801, United States

ACS Catal., 2018, 8, pp 2296–2312
DOI: 10.1021/acscatal.7b04201

The catalytic exchange of hydrogen and deuterium (H/D exchange) in light alkanes has been studied for almost a century. While alkanes and their C–H bonds are relatively inert, H/D exchange studies have shown that a large number of materials can catalytically activate these bonds. These studies helped elucidate the mechanisms by which alkane C–H bonds interact with catalytic materials. This Review serves to highlight this area of research, focusing on two main classes of heterogeneous materials, metals and metal oxides, and their trends in reactivities and selectivities are described in detail. Furthermore, the ability of these materials to carry out C–H bond activation and H/D exchange catalysis is compared with that of molecular organometallic complexes, and the mechanistic relationships and similarities in these processes are proposed.

Keywords: 

alkanes; C−H activation; deuterium; H/D exchange; isotopes; mechanism

Light-Driven CH Oxygenation of Methane into Methanol and Formic Acid by Molecular Oxygen Using a Perfluorinated Solvent

Light-Driven CH Oxygenation of Methane into Methanol and Formic

Acid by Molecular Oxygen Using a Perfluorinated Solvent

Angew. Chem. Int. Ed. 2017, 56, 1-5 

http://onlinelibrary.wiley.com/doi/10.1002/anie.201710945/epdf

Abstract:

The chlorine dioxide radical (ClO2·) was found to act as an efficient oxidizing agent in the aerobic oxygenation of methane to methanol and formic acid under photoirradiation. Photochemical oxygenation of methane occurred in a two-phase system comprising perfluorohexane and water under

ambient conditions (298 K, 1 atm). The yields of methanol and formic acid were 14 and 85 %, respectively, with a methane conversion of 99% without formation of the further oxygenated products such as CO2and CO. Ethane was also photochemically converted into ethanol (19%) and acetic acid (80%). The methane oxygenation is initiated by the photochemical Cl-O bond cleavage of ClO2· to generate Cl· and O2. The produced Cl· reacts with CH4 to form a methyl radical (CH3·). Finally, the oxygenated products such as methanol and formic acid were given by the radical chain reaction. A fluorous solvent plays an important role of inhibiting the deactivation of reactive radical species such as Cl· and CH3·.