7 research outputs found
Diels–Alder via Molecular Recognition in a Crystalline Molecular Flask
In the pore of a porous coordination network, Diels–Alder reactants, a diene and a dienophile, are recognized by donor–acceptor and multiple H-bond interactions, respectively, and fixed at ideal positions for the reaction. Heating the crystals promoted the Diels–Alder reactions with enhanced reactivity and controlled regioselectivity as clearly monitored by in situ X-ray crystallography
X‑ray Snapshot Observation of Palladium-Mediated Aromatic Bromination in a Porous Complex
Pd-mediated
aromatic bromination is intriguing to synthetic and
organometallic chemists due to both its synthetic utility and, more
importantly, a proposed mechanism involving an uncommon PdÂ(IV)/PdÂ(II)
catalytic cycle. Here, we report an X-ray snapshot observation of
a Pd reaction center during a Pd-mediated aromatic bromination in
a single crystal of a porous coordination network crystalline scaffold.
Upon treatment of a single crystal with <i>N</i>-bromosuccinimide,
sequential X-ray snapshots revealed that the aryl-PdÂ(II)-L species
embedded in the network pores was converted to the brominated aryl
product through a transient aryl-PdÂ(II)-Br species, which is normally
unobservable because of its rapid dimerization into insoluble Pd<sub>2</sub>(μ-Br)<sub>2</sub> species. Though the reaction pathway
may be biased by the crystalline state, the new X-ray snapshot method
relies on crystalline flasks to provide important mechanistic insight
Networked-Cage Microcrystals for Evaluation of Host–Guest Interactions
We
have developed a new synthetic protocol for the preparation
of a microcrystalline powder (median size: <i>X</i><sub>50</sub> = 25 μm) of networked M<sub>6</sub>L<sub>4</sub> cages <b>1a</b> for the stationary phase of an affinity column on a greater
than 50 g scale. Analogously to large single crystals <b>1b</b> (<i>X</i><sub>50</sub> ≈ 0.5 mm), microcrystals <b>1a</b> accommodate guest molecules tetrathiafulvalene (TTF) and
fullerene (C<sub>60</sub>) at up to 32 and 35 wt %, respectively.
Importantly, the host–guest interactions within networked cages
could be evaluated in terms of the retention time from HPLC analysis
by using microcrystals <b>1a</b> as the stationary phase. In
this way, favorable guests for networked cages <b>1</b> and
even solution M<sub>6</sub>L<sub>4</sub> cage <b>2</b> could
easily be assessed by HPLC
Cyclo‑<i>meta</i>‑phenylene Revisited: Nickel-Mediated Synthesis, Molecular Structures, and Device Applications
From a one-pot nickel-mediated Yamamoto-type
coupling reaction
of <i>m</i>-dibromobenzene, five congeners of [<i>n</i>]Âcyclo-<i>meta</i>-phenylenes were synthesized and fully
characterized. The [<i>n</i>]Âcyclo-<i>meta</i>-phenylenes possessed a commonly shared arylene unit and intermolecular
contacts but varied in packing structures in the crystalline solid
state. Columnar assembly of larger congeners yielded nanoporous crystals
with carbonaceous walls to capture minor protic or aliphatic solvent
molecules. The concise and scalable synthesis allowed exploration
of the macrocyclic hydrocarbons as bipolar charge carrier transport
materials in organic light-emitting diode devices
Modular Synthesis of Aromatic Hydrocarbon Macrocycles for Simplified, Single-Layer Organic Light-Emitting Devices
A method
for the modular synthesis of aromatic hydrocarbon macrocycles
has been developed for base materials in single-layer organic light-emitting
devices. The method with Ir-catalyzed direct C–H borylation
and Suzuki–Miyaura coupling was concise and scalable, which
allowed for a gram-scale preparation of aromatic hydrocarbon macrocycles
that have bulky substituents at the periphery. The new arylated hydrocarbon
macrocycles enabled a quantitative electro-optical conversion in organic
light-emitting devices with a phosphorescent emitter, which is, notably,
in a single-layer architecture consisting of two regions of doped
and undoped materials. The highest external quantum efficiencies reached
24.8%, surpassing those of previous hydrocarbon base materials