1693-74-9Relevant articles and documents
Proton Chemical Shifts and Thermodynamics of the Formation of Hydrogen-Bonded Dimers and Mixed 1:1 Associates in the Ternary System Acetic Acid/Methanol/Tetrahydrofuran-d8
Gerritzen, Detlef,Limbach, Hans-Heinrich
, p. 799 - 805 (1980)
The chemical shifts of the carboxylic proton of acetic acid and of the hydroxylic proton of methanol dissolved together and separately in tetrahydrofuran-d8 were determined as a function of the temperature and the solute concentrations.The determination of these chemical shifts was possible because in very pure samples the line positions are not affected by proton-exchange reactions.The data can only be explained by the presence of the following association reactions between hydrogen-bonded species which involve the solvent, S: RCOOH...S + RCOOH...S RCOOH...RCOOH...S + S RCOOH...S +ROH...S RCOOH...ROH...S + S ROH...S + RCOOH...S ROH...RCOOH...S + S ROH...S + ROH...S ROH...ROH...S + S The reaction enthalpies are given by +4.2, -1.4, -3.0, and -3.3 kJ mol-1, the reaction entropies at 298 K by +0.3, -3, -9, and -16 J K-1 mol-1.These data are not very far from zero, indicating that the number of hydrogen bonds remains constant during the association.Nevertheless, the extent of association is very low, and the quasi monomers which are hydrogen bonded to the solvent dominate.This arises from the high concentration, cs, of the free solvent.The change of cs at higher solute concentrations has to be taken into account in the treatment of the experimental data.Similarly, hydrogen bonding between the donors and the solvent is the reason that cyclic 1:1 associates and higher associates are not observed and the reason for the slow proton exchange.It is shown that the thermodynamic data of proton donor association in different media obey linear enthalpy-entropy relationships which are typical for the functional proton donor group.
Iridium Hydride Complexes with Cyclohexyl-Based Pincer Ligands: Fluxionality and Deuterium Exchange
Polukeev, Alexey V.,Marcos, Rocío,Ahlquist, M?rten S. G.,Wendt, Ola F.
, p. 2600 - 2608 (2016/09/04)
Two hydride compounds with aliphatic pincer ligands, (PCyP)IrH2 (PCyP = {cis-1,3-bis[(di-tert-butylphosphino)methyl]cyclohexane}- (1) and (PCyP)IrH4 (2), have been studied, with emphasis on features where such systems differ from arene-based analogues. Both compounds reveal relatively rapid exchange between α-C-H and Ir-H, which can occur via formation of carbene or through demetalation, with nearly equal barriers. This observation is confirmed by deuterium incorporation into the α-C-H position. Complex 1 can reversibly add an N2 molecule, which competes with the α-agostic bond for a coordination site at iridium. The hydrogen binding mode in tetrahydride 2 is discussed on the basis of NMR and IR spectra, as well as DFT calculations. While the interpretation of the data is somewhat ambiguous, the best model seems to be a tetrahydride with minor contribution from a dihydrido-dihydrogen complex. In addition, the catalytic activity of 1 in deuterium exchange using benzene-d6 as a deuterium source is presented.
Iridium-catalyzed H/D exchange into organic compounds in water
Klei, Steven R.,Golden, Jeffrey T.,Tilley, T. Don,Bergman, Robert G.
, p. 2092 - 2093 (2007/10/03)
The air-stable complex Cp*(PMe3)IrCl2 efficiently catalyzes the exchange of deuterium from D2O into both activated and unactivated C-H bonds of organic molecules without added acid or stabilizers. Selectivity is observed in many cases, with activation of primary C-H bonds occurring preferentially. A number of new stoichiometric transformations involving the iridiym catalyst precursor are also presented, including an ozidation-decarbonylation reaction with primary alcohols. Copyright
