338800-20-7Relevant articles and documents
Temperature and Solvent Effects on H2Splitting and Hydricity: Ramifications on CO2Hydrogenation by a Rhenium Pincer Catalyst
Hu, Jenny,Bruch, Quinton J.,Miller, Alexander J. M.
, p. 945 - 954 (2021)
The catalytic hydrogenation of carbon dioxide holds immense promise for applications in sustainable fuel synthesis and hydrogen storage. Mechanistic studies that connect thermodynamic parameters with the kinetics of catalysis can provide new understanding and guide predictive design of improved catalysts. Reported here are thermochemical and kinetic analyses of a new pincer-ligated rhenium complex (tBuPOCOP)Re(CO)2 (tBuPOCOP = 2,6-bis(di-tert-butylphosphinito)phenyl) that catalyzes CO2 hydrogenation to formate with faster rates at lower temperatures. Because the catalyst follows the prototypical outer sphere hydrogenation mechanism, comprehensive studies of temperature and solvent effects on the H2 splitting and hydride transfer steps are expected to be relevant to many other catalysts. Strikingly large entropy associated with cleavage of H2 results in a strong temperature dependence on the concentration of [(tBuPOCOP)Re(CO)2H]- present during catalysis, which is further impacted by changing the solvent from toluene to tetrahydrofuran to acetonitrile. New methods for determining the hydricity of metal hydrides and formate at temperatures other than 298 K are developed, providing insight into how temperature can influence the favorability of hydride transfer during catalysis. These thermochemical insights guided the selection of conditions for CO2 hydrogenation to formate with high activity (up to 364 h-1 at 1 atm or 3330 h-1 at 20 atm of 1:1 H2:CO2). In cases where hydride transfer is the highest individual kinetic barrier, entropic contributions to outer sphere H2 splitting lead to a unique temperature dependence: catalytic activity increases as temperature decreases in tetrahydrofuran (200-fold increase upon cooling from 50 to 0 °C) and toluene (4-fold increase upon cooling from 100 to 50 °C). Ramifications on catalyst structure-function relationships are discussed, including comparisons between outer sphere mechanisms and metal-ligand cooperation mechanisms.
POCOP-Type Pincer Complexes of Nickel: Synthesis, Characterization, and Ligand Exchange Reactivities of New Cationic Acetonitrile Adducts
Lapointe, Sbastien,Vabre, Boris,Zargarian, Davit
, p. 3520 - 3531 (2015/08/06)
This report describes the synthesis, characterization, and ligand exchange studies of a family of cationic acetonitrile adducts of nickel featuring resorcinol-based, pincer-type POCOP ligands. The compounds [(R-POCOPR′)Ni(NCMe)][OSO2CF3] (R-POCOPR′ = 2,6-(R′2PO)2(RnC6H3-n); R′ = i-Pr: R = H (1), p-Me (2), p-OMe (3), p-CO2Me (4), p-Br (5), m,m-t-Bu2 (6), m-OMe (7), m-CO2Me (8); R′ = t-Bu: R = H (9), p-CO2Me (10)) were prepared in 80-93% yields by reacting the corresponding charge-neutral bromo derivatives with Ag(OSO2CF3) in acetonitrile. The impact of the R- and R′-substituents on electronics and structures of 1-10 have been probed by NMR, UV-vis, and IR spectra, X-ray crystallography, and cyclic voltammetry measurements. The observed ν(C≡N) values were found to increase with the increasing electron-withdrawing nature of R, i.e., in the order 7 2C-substituted cations showed the highest oxidation potentials. Moreover, all cationic adducts showed greater oxidation potentials compared with their corresponding charge-neutral bromo precursors. Equilibrium studies conducted with selected [(R-POCOPR′)Ni(NCMe)][OSO2CF3] and (R-POCOPR′)NiBr (R′ = i-Pr) have confirmed facile MeCN/Br exchange between these derivatives and show that the cationic adducts are stabilized with MeO-POCOP, whereas the charge-neutral bromo species are stabilized with MeO2C-POCOP. The potential implications of these findings for the catalytic reactivities of the title cationic complexes have been discussed. (Chemical Equation Presented).
Iridium Bis(phosphinite) p-XPCP Pincer Complexes: Highly Active Catalysts for the Transfer Dehydrogenation of Alkanes
G?ttker-Schnetmann, Inigo,White, Peter,Brookhart, Maurice
, p. 1804 - 1811 (2007/10/03)
A series of new bis(phosphinite) p-XPCPlrHCl pincer complexes {[PCP = η3-5-X-C6H2[OP-(tBu)2] 2-1,3], X = MeO (4a), Me (4b), H (4c), F (4d), C6F 5 (4e), and ArF [=3,5-bis(trifluoromethyl)phenyl] (4f)} have been synthesized. Treatment of compounds 4a-f with NatOBu in cyclooctane (COA)/tert-butylethylene (TBE) mixtures generates species with unprecedented catalytic activity for the catalyzed transfer dehydrogenation of COA with TBE as acceptor to form cyclooctene (COE) and tert-butylethane (TBA). With substrate: precatalyst ratios of 3030COA:3030TBE:1 p-XPCPlrHCl (4): 1.1NaOtBu, turnover numbers (TONs) between 1400 and 2200 (up to 72% conversion in TBE) and initial turnover frequencies (TOFs) between 1.6 and 2.4 s-1 have been observed at 200 °C.
