43 research outputs found
Self-Similarity and Localization
The localized eigenstates of the Harper equation exhibit universal
self-similar fluctuations once the exponentially decaying part of a wave
function is factorized out. For a fixed quantum state, we show that the whole
localized phase is characterized by a single strong coupling fixed point of the
renormalization equations. This fixed point also describes the generalized
Harper model with next nearest neighbor interaction below a certain threshold.
Above the threshold, the fluctuations in the generalized Harper model are
described by a strange invariant set of the renormalization equations.Comment: 4 pages, RevTeX, 2 figures include
Metastability and Phase Separation in a Simple Model of a Superconductor with Extremely Short Coherence Length
Identification and counting of carbonyl and hydroxyl functionalities in protonated bifunctional analytes by using solution derivatization prior to mass spectrometric analysis via ion-molecule reactions
Bis-N-heterocyclic carbene aminopincer ligands enable high activity in Ru-catalyzed ester hydrogenation
Bis-N-heterocyclic carbene (NHC) aminopincer ligands were for the first time successfully applied in catalytic hydrogenation of esters. We have isolated and characterized a well-defined catalyst precursor as a dimeric [Ru2(L)2Cl3]PF6 complex and studied its reactivity and catalytic performance. Remarkable initial activities up to 283 000 h-1 were achieved in hydrogenation of ethyl hexanoate at only 12.5 ppm Ru loading. A wide range of aliphatic and aromatic esters can be converted with this catalyst to corresponding alcohols in near quan-titative yields. The described synthetic protocol makes use of air stable reagents available in multigram quantities rendering the bis-NHC ligands an attractive alternative to the conventional phosphine-based systems
Bis-N-heterocyclic carbene aminopincer ligands enable high activity in Ru-catalyzed ester hydrogenation
Bis-N-heterocyclic carbene (NHC) aminopincer ligands were for the first time successfully applied in catalytic hydrogenation of esters. We have isolated and characterized a well-defined catalyst precursor as a dimeric [Ru2(L)2Cl3]PF6 complex and studied its reactivity and catalytic performance. Remarkable initial activities up to 283 000 h-1 were achieved in hydrogenation of ethyl hexanoate at only 12.5 ppm Ru loading. A wide range of aliphatic and aromatic esters can be converted with this catalyst to corresponding alcohols in near quan-titative yields. The described synthetic protocol makes use of air stable reagents available in multigram quantities rendering the bis-NHC ligands an attractive alternative to the conventional phosphine-based systems
Triazaphospholes versus Triazoles: An Investigation of the Differences between “Click”-Derived Chelating Phosphorus- and Nitrogen-Containing Heterocycles
A new
class of pyridyl-functionalized triazaphospholes bearing
either <sup><i>t</i></sup>Bu or SiMe<sub>3</sub> substituents
at the 5-position of the N<sub>3</sub>PC heterocycle have been prepared
via the “click” reaction starting from 2-(azidomethyl)pyridine
and the corresponding phosphaalkynes. In order to investigate the
electronic structure and donor–acceptor properties of such
novel chelating and low-coordinate phosphorus heterocycles, calculations
at the DFT level have been carried out. Moreover, cyclic voltammetry
measurements were performed and the results were compared with those
for the structurally related triazole-based systems, demonstrating
a significant influence of the phosphorus atom as well as the substitution
pattern on the electronic properties of the novel compounds. The P,N
hybrid ligands form Re(I) complexes of the type [(N<sup>∧</sup><sup>m</sup>N)Re(CO)<sub>3</sub>Br] via coordination of the nitrogen
atom N<sup>2</sup> to the metal center rather than via the phosphorus
atom, as verified crystallographically