The manner of bonding between constituent
atoms or molecules invariably
influences the properties of materials. Perhaps no material family
is more emblematic of this than porous frameworks, wherein the namesake
modes of connectivity give rise to discrete subclasses with unique
collections of properties. However, established framework classes
often display offsetting advantages and disadvantages for a given
application. Thus, there exists no universally applicable material,
and the discovery of alternative modes of framework connectivity is
highly desirable. Here we show that chalcogen bonding, a subclass
of σ-hole bonding, is a viable mode of connectivity in low-density
porous frameworks. Crystallization studies with the triptycene tris(1,2,5-selenadiazole)
molecular tecton reveal how chalcogen bonding can template high-energy
lattice structures and how solvent conditions can be rationalized
to obtain molecularly programmed porous chalcogen-bonded organic frameworks
(ChOFs). These results provide the first evidence that σ-hole
bonding can be used to advance the diversity of porous framework materials.
The synthesis, structural, and electronic properties of nine 1,3-diphenyl-6-alkyl/aryl substituted pentafulvenes were studied. Pyrene ring π-π interactions were revealed from analysis of the experimental crystal packing of 1,3-diphenyl-6-(1-pyrene)fulvene and supporting DFT calculations. Photophysical properties derived from UV-vis and fluorescence emission measurements demonstrated tunable and low HOMO-LUMO band gaps for the series. The presented results point to a model synthetic approach for incorporation of extended π systems and donor-π-acceptor groups for fulvene-based electronic materials.
A variety of titanium aryloxide reagents catalyze the cross
coupling of two alkyne units with 1 equiv of
olefin to produce the 1,3-cyclohexadiene nucleus. Catalysts
include isolated titanacyclopentadiene or
titanacyclopentane
complexes. The reaction proceeds via attack of the olefin upon a
titanacyclopentadiene compound initially formed
by coupling of two alkyne units. The reaction is limited to bulky
alkyne substrates that undergo slow catalytic
cyclotrimerization via competing attack of a third alkyne upon the
titanacyclopentadiene ring. The organic products
isolated are typically the result of an isomerization within the
initially produced 1,3-cyclohexadiene nucleus.
Mechanistic studies show that these isomerization processes occur
via sequential, metal-mediated 1,5-hydrogen shifts
upon a single face of the six-membered ring, exclusively leading to a
cis-stereochemistry within the final products.
In the reactions of the diynes
RC⋮C(CH2)4C⋮CR (R = Et,
SiMe3), coupling with ethylene and α-olefins
produces
a variety of substituted hexalins. A combination of NMR
spectroscopy, photochemistry, and molecular mechanics
calculations has been applied to determine the stereochemistry and
ground state conformations adopted by the product
1,3-cyclohexadienes and hexalins. The primary and secondary
photoproducts obtained from some of these 1,3-cyclohexadiene compounds have been characterized.
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