22161-90-6Relevant academic research and scientific papers
A practical procedure for iron-catalyzed cross-coupling reactions of sterically hindered aryl-grignard reagents with primary alkyl halides
Sun, Chang-Liang,Krause, Helga,Fuerstner, Alois
, p. 1281 - 1291 (2014)
Although iron-catalyzed cross-coupling reactions of arylmagnesium halides with alkyl halides are well established and proceed effectively under a variety of experimental conditions, they often find limitations when working with sterically hindered aryl-Grignard reagents. Outlined in this paper is a practical solution that allows this gap in coverage to be filled. Specifically, it is shown that bis(diethylphosphino)ethane (depe) crafts an effective coordination environment about Fe(+2). This commercially available ligand is slim enough not to interfere with the loading of the iron center even by ortho,ortho-disubstituted arylmagnesium halides, yet capable of preventing premature reductive coupling of the resulting organoiron species, which seem to be hardly basic either. The reaction is compatible with various polar functional groups as well as with substrates containing β-heteroatom substituents. Moreover, the procedure even allows encumbered neopentylic electrophiles to be arylated with donors as bulky as mesitylmagnesium bromide, whereas secondary alkyl halides tend to eliminate.
Design of liquid crystalline block molecules with nonconventional mesophase morphologies: Calamitic bolaamphiphiles with lateral alkyl chains
Koelbel,Beyersdorff,Xiao Hong Cheng,Tschierske,Kain,Diele
, p. 6809 - 6818 (2007/10/03)
Novel bolaamphiphiles, consisting of a biphenyl rigid core, polar 2,3-dihydroxypropoxy groups at each terminal end, and an additional long alkyl chain in a lateral position have been synthesized. The structures of these ternary block molecules were systematically changed by variation of the length and position of the alkyl chain, by introduction of additional spacer units between one of the 2,3-dihydroxypropyl groups and the rigid core, and by replacement of one of the 2,3-dihydroxypropoxy groups by a single hydroxy group. The influence of these structural variations on the liquid crystalline properties of these new materials was investigated by polarized-light microscopy, differential scanning calorimetry, and X-ray diffraction. These investigation have shown that, by elongation of the lateral chain, a transition from a smectic monolayer structure (SmA1) via a strongly distorted layer structure (SmA+), a centered rectangular columnar phase (Colr/c2mm) and a noncentered rectangular columnar phase (Colr/p2gg) to a hexagonal columnar phase (Colh/p6mm) takes place. Elongation of the bolaamphiphilic core leads to the loss of the columnar phases, which are replaced by smectic phases, whereas reduction of its length favors the hexagonal columnar phase. This phase sequence is explained as a result of the microsegregation of the lateral alkyl chains from the rigid aromatic cores. The segregated alkyl chains are organized in columns that interrupt the smectic layers. The hydrogen bonding keep the bolaamphiphilic cores fixed end to end, so that they form networks of cylinders around the lipophilic columns. The space required by the alkyl chains with respect to the length of the bolaamphiphilic cores is restricted and largely determines the geometry of the cylinders, which leads to the observed phase sequence. The obtained mesophase morphologies, built up by three distinct sets of subspaces, are related to morphologies of some ternary block copolymers. Furthermore, the investigated compounds represent a novel class of materials, capable of forming supramolecular columnar mesophases.
