931-88-4Relevant articles and documents
Diverse Mechanistic Pathways in Single-Site Heterogeneous Catalysis: Alcohol Conversions Mediated by a High-Valent Carbon-Supported Molybdenum-Dioxo Catalyst
Bedzyk, Michael J.,Das, Anusheela,Kratish, Yosi,Li, Jiaqi,Ma, Qing,Marks, Tobin J.
, p. 1247 - 1257 (2022/02/07)
With the increase in the importance of renewable resources, chemical research is shifting focus toward substituting petrochemicals with biomass-derived analogues and platform-molecule transformations such as alcohol processing. To these ends, in-depth mechanistic understanding is key to the rational design of catalytic systems with enhanced activity and selectivity. Here we discuss in detail the structure and reactivity of a single-site active carbon-supported molybdenum-dioxo catalyst (AC/MoO2) and the mechanism(s) by which it mediates alcohol dehydration. A range of tertiary, secondary, and primary alcohols as well as selected bio-based terpineols are investigated as substrates under mild reaction conditions. A combined experimental substituent effect/kinetic/kinetic isotope effect/EXAFS/DFT computational analysis indicates that (1) water assistance is a key element in the transition state; (2) the experimental kinetic isotopic effect and activation enthalpy are 2.5 and 24.4 kcal/mol, respectively, in good agreement with the DFT results; and (3) several computationally identified intermediates including Mo-oxo-hydroxy-alkoxide and cage-structured long-range water-coordinated Mo-dioxo species are supported by EXAFS. This structurally and mechanistically well-characterized single-site system not only effects efficient transformations but also provides insight into rational catalyst design for future biomass processes.
Catalytic Dehydrogenation of Alkanes by PCP-Pincer Iridium Complexes Using Proton and Electron Acceptors
Shada, Arun Dixith Reddy,Miller, Alexander J. M.,Emge, Thomas J.,Goldman, Alan S.
, p. 3009 - 3016 (2021/03/09)
Dehydrogenation to give olefins offers the most broadly applicable route to the chemical transformation of alkanes. Transition-metal-based catalysts can selectively dehydrogenate alkanes using either olefinic sacrificial acceptors or a purge mechanism to remove H2; both of these approaches have significant practical limitations. Here, we report the use of pincer-ligated iridium complexes to achieve alkane dehydrogenation by proton-coupled electron transfer, using pairs of oxidants and bases as proton and electron acceptors. Up to 97% yield was achieved with respect to oxidant and base, and up to 15 catalytic turnovers with respect to iridium, using t-butoxide as base coupled with various oxidants, including oxidants with very low reduction potentials. Mechanistic studies indicate that (pincer)IrH2 complexes react with oxidants and base to give the corresponding cationic (pincer)IrH+ complex, which is subsequently deprotonated by a second equivalent of base; this affords (pincer)Ir which is known to dehydrogenate alkanes and thereby regenerates (pincer)IrH2.
Organometallic iridium complexes of (Z)-1-Phenyl-2-(4′,4′-dimethyl-2′-oxazolin-2′-yl)-eth-1-en-1-ate: Structural aspects, reactivity and applications in the catalytic dehydrogenation of Alkanes#
Clément, Roxanne,Gossage, Robert A.,Lough, Alan J.,May, Kathleen L.
supporting information, p. 2042 - 2047 (2021/09/16)
The treatment of [IrCl(cod)]2 with (Z)-1-phenyl-2-(4′,4′- dimethyl-2′-oxazolin-2′-yl)-eth-1-en-1-ol (HL) in the presence of base yields the first Ir complex of this ligand class: Ir(κ2- N,O-L)(cod) (3). Complex 3 is reactive with MeI or HSnPh3 to yield the oxidative addition products 4 (trans-Ir(Me)I(κ2-N,OL)( cod)) and 5 (cis-IrH(SnPh3)(κ2-N,O-L)(cod)), respectively. All three of these derivatives have been fully characterised including via single crystal X-ray diffraction data. Complex 3 is generally resistant to cod ligand substitution but shown to be reactive with CO (g) to give Ir(κ2-N,O-L)(CO)2 (6). In addition, 3 is demonstrated to be a dehydrogenation catalyst for the conversion of C8H16 into cyclooctene and H2 under acceptorfree conditions.