5 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
X‑ray Structure Analysis of Ozonides by the Crystalline Sponge Method
The crystalline sponge
method was used for the X-ray structure
analysis of ozonide compounds. As this new technique requires only
microgram quantities of the samples, structural analysis can be conducted
without product isolation, isomer separation, or crystallization and
most importantly without any risk of explosion
Chiral Crystalline Sponges for the Absolute Structure Determination of Chiral Guests
Chiral crystalline sponges with preinstalled
chiral references
were synthesized. On the basis of the known configurations of the
chiral references, the absolute structures of guest compounds absorbed
in the pores of the crystalline sponges can be reliably determined
without crystallization or chemical modification
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