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997.
Weiheng Huang Dr. Xinxin Tian Prof. Haijun Jiao Dr. Ralf Jackstell Prof. Dr. Matthias Beller 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(9):e202104012
A novel one-pot iridium-catalyzed domino hydroxymethylation of olefins, which relies on using two different ligands at the same time, is reported. DFT computation reveals different activities for the individual hydroformylation and hydrogenation steps in the presence of mono- and bidentate ligands. Whereas bidentate ligands have higher hydrogenation activity, monodentate ligands show higher hydroformylation activity. Accordingly, a catalyst system is introduced that uses dual ligands in the whole domino process. Control experiments show that the overall selectivity is kinetically controlled. Both computation and experiment explain the function of the two optimized ligands during the domino process. 相似文献
998.
Lasse Hunger Loai Al-Sheakh Dr. Dzmitry H. Zaitsau Prof. Dr. Sergey P. Verevkin Andreas Appelhagen Dr. Alexander Villinger Prof. Dr. Ralf Ludwig 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(46):e202200949
We show that the carboxyl-functionalized ionic liquid 1-(carboxymethyl)pyridinium bis(trifluoromethylsulfonyl)imide [HOOC-CH2-py][NTf2] exhibits three types of hydrogen bonding: the expected single hydrogen bonds between cation and anion, and, surprisingly, single and double hydrogen bonds between the cations, despite the repulsive Coulomb forces between the ions of like charge. Combining X-ray crystallography, differential scanning calorimetry, IR spectroscopy, thermodynamic methods and DFT calculations allows the analysis and characterization of all types of hydrogen bonding present in the solid, liquid and gaseous states of the ionic liquid (IL). We find doubly hydrogen bonded cationic dimers (c+=c+) in the crystalline phase. With increasing temperature, this binding motif opens in the liquid and is replaced by (c+−c+−a− species, with a remaining single cationic hydrogen bond and an additional hydrogen bond between cation and anion. We provide clear evidence that the IL evaporates as hydrogen-bonded ion pairs (c+−a−) into the gas phase. The measured transition enthalpies allow the noncovalent interactions to be dissected and the hydrogen bond strength between ions of like charge to be determined. 相似文献
999.
Alexander E. Khudozhitkov Masaki Donoshita Prof. Dr. Alexander G. Stepanov Dr. Frederik Philippi Dr. Daniel Rauber Prof. Dr. Rolf Hempelmann Prof. Dr. Hiroshi Kitagawa Dr. Daniil I. Kolokolov Prof. Dr. Ralf Ludwig 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(23):e202200257
We report the complex phase behavior of the glass forming protic ionic liquid (PIL) d3-octylphosphonium bis(trifluoromethylsulfonyl)imide [C8H17PD3][NTf2] by means of solid-state NMR spectroscopy. Combined line shape and spin relaxation studies of the deuterons in the PD3 group of the octylphosphonium cation allow to map and correlate the phase behavior for a broad temperature range from 71 K to 343 K. In the solid PIL at 71 K, we observed a static state, characterized by the first deuteron quadrupole coupling constant reported for PD3 deuterons. A transition enthalpy of about 12 kJ mol−1 from the static to the mobile state with increasing temperature suggests the breaking of a weak, charge-enhanced hydrogen bond between cation and anion. The highly mobile phase above 100 K exhibits an almost disappearing activation barrier, strongly indicating quantum tunneling. Thus, we provide first evidence of tunneling driven mobility of the hydrogen bonded P−D moieties in the glassy state of PILs, already at surprisingly high temperatures up to 200 K. Above 250 K, the mobile phase turns from anisotropic to isotropic motion, and indicates strong internal rotation of the PD3 group. The analyzed line shapes and spin relaxation times allow us to link the structural and dynamical behavior at molecular level with the phase behavior beyond the DSC traces. 相似文献
1000.
Ralf Hofmann 《Annalen der Physik》2015,527(3-4):254-264
Presuming that CMB photons are described by the deconfining phase of an SU(2) Yang‐Mills theory with the critical temperature for the deconfining‐preconfining phase transition matching the present CMB temperature K (SU(2)CMB), we investigate how CMB temperature T connects with the cosmological scale factor a in a Friedmann‐Lemaître‐Robertson‐Walker Universe. Owing to a violation of conformal scaling at late times, the tension between the (instantaneous) redshift of reionisation from CMB observation () and quasar spectra () is repealed. Also, we find that the redshift of CMB decoupling moves from to which questions ΛCDM cosmology at high redshifts. Adapting this model to the conventional physics of three flavours of massless cosmic neutrinos, we demonstrate inconsistency with the value Neff ~ 3.36 extracted from Planck data. Interactions between cosmic neutrinos and the CMB implies a common temperature T of (no longer separately conserved) CMB and neutrino fluids. Neff ~ 3.36 then entails a universal, temperature induced cosmic neutrino mass with . Our above results on zre and zdec, derived from SU(2)CMB alone, are essentially unaffected when including such a neutrino sector.