Globale Migration am Beginn des 21. Jahrhunderts : Eine Welt ohne Grenzen? Dokumentation der internationalen Fachtagung vom 30./31. Mai 2006 in Berlin

Nonafluorobutanesulfonyl azide is a highly efficient reagent for the copper-catalyzed coupling of terminal alkynes to give symmetrical and unsymmetrical 1,3-diynes in good to excellent yields and with good functional group compatibility. The reaction is extremely fast (<10 min), even at low temperature (−78 °C), and requires substoichiometric amounts of a simple copper­(I) or copper­(II) salt (2–5 mol %) and an organic base (0.6 mol %). A possible mechanistic pathway is briefly discussed on the basis of model DFT theoretical calculations. The quantitative assessment of the safety of use and shelf stability of nonafluorobutanesulfonyl azide has confirmed that this reagent is a superior and safe alternative to other electrophilic azide reagents in use today

Palladium-Catalyzed Acetoxylation of Arenes by Novel Sulfinyl N‑Heterocyclic Carbene Ligand Complexes

A series of novel ligands based on N-heterocyclic carbene and sulfoxide functionalities have been prepared and characterized. Pd­(II) complexes have been synthesized by transmetalation from the corresponding NHC–Ag derivatives, and their behavior as catalysts has been studied in arene C–H bond oxidative activation. Studies conducted toward the elucidation of the reaction mechanism of the acetoxylation suggest a C–H activation step at Pd­(IV) rather than Pd­(II) intermediates

Palladium-Catalyzed Acetoxylation of Arenes by Novel Sulfinyl N‑Heterocyclic Carbene Ligand Complexes

A series of novel ligands based on N-heterocyclic carbene and sulfoxide functionalities have been prepared and characterized. Pd­(II) complexes have been synthesized by transmetalation from the corresponding NHC–Ag derivatives, and their behavior as catalysts has been studied in arene C–H bond oxidative activation. Studies conducted toward the elucidation of the reaction mechanism of the acetoxylation suggest a C–H activation step at Pd­(IV) rather than Pd­(II) intermediates

Ligand-Controlled Electron Structure of Catalytically Active Ni Complexes

We have performed a systematic study of the electron structure of a series of Ni­(I) and Ni­(II) iodo and methyl complexes with a variety of di- and tridentate nitrogen ligands to study the influence of these ligands in the structure of catalytically active complexes in cross-coupling reactions. Ni­(II) compounds show the expected square-planar configuration typical of complexes of d⁸ metals, regardless of the kind of coordinating nitrogen atom (sp² or sp³) found in ligands derived from either trialkylamines or pyridines. In contrast, Ni­(I) complexes show different structures. Thus, the absence of orbitals capable of delocalizing the unpaired electron (such as in TMEDA and PMDTA derivatives) leads to nonplanar iodo or methyl tetracoordinate complexes. In contrast, the presence of ligands derived from pyridine allows delocalization of the unpaired electron on the ligand. This delocalization is especially effective for terpyridine species

Ligand-Controlled Electron Structure of Catalytically Active Ni Complexes

We have performed a systematic study of the electron structure of a series of Ni­(I) and Ni­(II) iodo and methyl complexes with a variety of di- and tridentate nitrogen ligands to study the influence of these ligands in the structure of catalytically active complexes in cross-coupling reactions. Ni­(II) compounds show the expected square-planar configuration typical of complexes of d⁸ metals, regardless of the kind of coordinating nitrogen atom (sp² or sp³) found in ligands derived from either trialkylamines or pyridines. In contrast, Ni­(I) complexes show different structures. Thus, the absence of orbitals capable of delocalizing the unpaired electron (such as in TMEDA and PMDTA derivatives) leads to nonplanar iodo or methyl tetracoordinate complexes. In contrast, the presence of ligands derived from pyridine allows delocalization of the unpaired electron on the ligand. This delocalization is especially effective for terpyridine species

Regiocontrolled Cu^I-Catalyzed Borylation of Propargylic-Functionalized Internal Alkynes

Good to excellent reactivity and regiocontrol have been achieved in the Cu^I-catalyzed borylation of dialkyl internal alkynes with bis­(pinacolato)­diboron. The presence of a propargylic polar group (OH, OR, SAr, SO₂Ar, or NHTs), in combination with PCy₃ as ligand, allowed maximizing the reactivity and site-selectivity (β to the propargylic function). DFT calculations suggest a subtle orbitalic influence from the propargylic group, matched with ligand and substrate size effects, as key factors involved in the high β-selectivity. The vinylboronates allowed the stereoselective synthesis of trisubstituted olefins, while allylic substitution of the SO₂Py group without affecting the boronate group provided access to formal hydroboration products of unbiased dialkylalkynes

Copper-Catalyzed Borylative Aromatization of <i>p</i>‑Quinone Methides: Enantioselective Synthesis of Dibenzylic Boronates

In this report, we establish that DM-Segphos copper­(I) complexes are efficient catalysts for the enantioselective borylation of <i>para</i>-quinone methides. This method provides straightforward access to chiral monobenzylic and dibenzylic boronic esters, with enantiomeric ratios up to 96:4, using a commercially available chiral phosphine. Standard manipulations of the C–B bond afford a variety of chiral diaryl derivatives

Development of a New Dual Polarity and Viscosity Probe Based on the Foldamer Concept

Small molecular probes able to act as sensors are of enormous interest thanks to their multiple applications. Here, we report on the development of a novel supramolecular dual viscosity and polarity probe based on the foldamer concept, which increases the resolution limits of traditional probes at low viscosity values (0–4 mPa·s). The applicability of this new probe has been tested with a supramolecular organogel