15 research outputs found
Synthesis, Structural Characterization, Aromatic Characteristics, and Metalation of Neo-Confused Porphyrins, a Newly Discovered Class of Porphyrin Isomers
Neo-confused
porphyrins represent a unique family of porphyrin isomers that retain overall aromatic
characteristics by virtue of a 17-atom 18Ļ electron delocalization
pathway. These porphyrin analogues have a pyrrolic subunit linked
in a 1,3-fashion so that a nitrogen atom is directly connected to
a <i>meso</i>-bridging carbon. Pyrrole-3-carbaldehydes were
shown to react with sodium hydride and 5-acetoxymethylpyrrole-2-carbaldehydes
in DMF to give the crucial neo-confused dipyrrolic dialdehyde intermediates.
MacDonald ā2 + 2ā condensation of the dialdehydes with
a dipyrrylmethane afforded a dihydroporphyrinoid, and subsequent oxidation
with 0.2% aqueous ferric chloride generated a series of fully conjugated
neo-confused porphyrins. Unusual dihydroporphyrin byproducts were
also identified. Reaction of neo-confused porphyrins with nickelĀ(II)
or palladiumĀ(II) acetate in refluxing acetonitrile gave excellent
yields of the corresponding organometallic derivatives. Proton NMR
spectroscopy demonstrates that the diatropic character of this system
is diminished compared to regular porphyrins, although neo-confused
porphyrins retain porphyrin-like UVāvis spectra. Protonation
led to the sequential formation of mono- and dicationic species. Proton
NMR spectra for the dications showed the presence of enhanced diamagnetic
ring currents
Synthesis, Structural Characterization, Aromatic Characteristics, and Metalation of Neo-Confused Porphyrins, a Newly Discovered Class of Porphyrin Isomers
Neo-confused
porphyrins represent a unique family of porphyrin isomers that retain overall aromatic
characteristics by virtue of a 17-atom 18Ļ electron delocalization
pathway. These porphyrin analogues have a pyrrolic subunit linked
in a 1,3-fashion so that a nitrogen atom is directly connected to
a <i>meso</i>-bridging carbon. Pyrrole-3-carbaldehydes were
shown to react with sodium hydride and 5-acetoxymethylpyrrole-2-carbaldehydes
in DMF to give the crucial neo-confused dipyrrolic dialdehyde intermediates.
MacDonald ā2 + 2ā condensation of the dialdehydes with
a dipyrrylmethane afforded a dihydroporphyrinoid, and subsequent oxidation
with 0.2% aqueous ferric chloride generated a series of fully conjugated
neo-confused porphyrins. Unusual dihydroporphyrin byproducts were
also identified. Reaction of neo-confused porphyrins with nickelĀ(II)
or palladiumĀ(II) acetate in refluxing acetonitrile gave excellent
yields of the corresponding organometallic derivatives. Proton NMR
spectroscopy demonstrates that the diatropic character of this system
is diminished compared to regular porphyrins, although neo-confused
porphyrins retain porphyrin-like UVāvis spectra. Protonation
led to the sequential formation of mono- and dicationic species. Proton
NMR spectra for the dications showed the presence of enhanced diamagnetic
ring currents
Preparation of Azulene-Derived Fulvenedialdehydes and Their Application to the Synthesis of Stable <i>adj</i>-Dicarbaporphyrinoids
A ā2 + 2ā strategy for synthesizing <i>adj</i>-dicarbaporphyrinoid systems has been developed. In a
model study, an azulenylmethylpyrrole dialdehyde was condensed with
a dipyrrylmethane in the presence of HCl, followed by oxidation with
ferric chloride, to give a modest yield of an azuliporphyrin. Fulvene
aldehydes were prepared by reacting an indene-derived enamine with
azulene aldehydes in the presence of Bu<sub>2</sub>BOTf, and azulene
dialdehydes similarly reacted to give fulvene dialdehydes. The dialdehydes
were condensed with dipyrrylmethanes in TFA/dichloromethane to afford
good to excellent yields of dicarbaporphyrinoids with adjacent indene
and azulene subunits. These 22-carbaazuliporphyrins exhibited significant
diatropic character, and this property was magnified upon protonation.
These characteristics are attributed to tropylium-containing resonance
contributors that possess 18Ļ electron delocalization pathways.
Protonation studies demonstrated that <i>C</i>-protonation
readily occurred at the interior indene carbon, but deuterium exchange
also occurred at the internal azulene CH as well as at the <i>meso</i>-positions with TFA-<i>d</i>. Reaction of
a carbaazuliporphyrin with silverĀ(I) acetate in methanol or ethanol
solutions also gave unusual nonaromatic dialkoxy derivatives
Preparation of Azulene-Derived Fulvenedialdehydes and Their Application to the Synthesis of Stable <i>adj</i>-Dicarbaporphyrinoids
A ā2 + 2ā strategy for synthesizing <i>adj</i>-dicarbaporphyrinoid systems has been developed. In a
model study, an azulenylmethylpyrrole dialdehyde was condensed with
a dipyrrylmethane in the presence of HCl, followed by oxidation with
ferric chloride, to give a modest yield of an azuliporphyrin. Fulvene
aldehydes were prepared by reacting an indene-derived enamine with
azulene aldehydes in the presence of Bu<sub>2</sub>BOTf, and azulene
dialdehydes similarly reacted to give fulvene dialdehydes. The dialdehydes
were condensed with dipyrrylmethanes in TFA/dichloromethane to afford
good to excellent yields of dicarbaporphyrinoids with adjacent indene
and azulene subunits. These 22-carbaazuliporphyrins exhibited significant
diatropic character, and this property was magnified upon protonation.
These characteristics are attributed to tropylium-containing resonance
contributors that possess 18Ļ electron delocalization pathways.
Protonation studies demonstrated that <i>C</i>-protonation
readily occurred at the interior indene carbon, but deuterium exchange
also occurred at the internal azulene CH as well as at the <i>meso</i>-positions with TFA-<i>d</i>. Reaction of
a carbaazuliporphyrin with silverĀ(I) acetate in methanol or ethanol
solutions also gave unusual nonaromatic dialkoxy derivatives
Lanthanide Texaphyrins as Photocatalysts
Here, we report the
use of gadoliniumĀ(III)-, lutetiumĀ(III)-, and lanthanumĀ(III)-texaphyrins
as bioinspired photocatalysts that promote a novel approach to the
degradation of curcumin, a 1,3-diketo-containing natural product.
Complexation of curcumin to the lanthanide centers of the texaphyrins
yields stable species that display limited reactivity in the dark
or under anaerobic conditions. However, upon exposure to mWatt intensity
light (pocket flashlight) or simply under standard laboratory illumination
in the presence of atmospheric oxygen, substrate oxidation occurs
readily to generate curcumin-derived cleavage products. These latter
species were identified on the basis of spectroscopic and mass spectrometric
analyses. The mild nature of the activation conditions serves to highlight
a potential new role for photoactive lanthanide complexes
Self-Assembled Pyridine-Dipyrrolate Cages
An
inherently nonlinear pyridine dipyrrolate ligand, namely 2,6-bisĀ(3,4-diethyl-5-carboxy-1<i>H</i>-pyrrol-2yl)Āpyridine (compound <b>1</b>), is able
to distinguish between different zincĀ(II) cation sources, namely ZnĀ(acac)<sub>2</sub> and ZnĀ(OAc)<sub>2</sub>, respectively. This differentiation
is manifest both in terms of the observed fluorescent behavior in
mixed organic media and the reaction chemistry. Treatment of <b>1</b> with ZnĀ(acac)<sub>2</sub> gives rise to a cage dimer, cage-<b>1</b>, wherein two molecules of compound <b>1</b> act as
double bridging units to connect two individual cage subunits. As
inferred from X-ray crystallographic studies, this cage system consists
of discrete zinc dimers with hydroxide bridges that, with the assistance
of bound DMF solvent molecules, serve to fix the geometry and orientation
of the pyridine dipyrrolate building blocks. When a different zinc
source, ZnĀ(OAc)<sub>2</sub>, is used to carry out an ostensibly similar
complexation reaction with compound <b>1</b>, an acetate-bridged
1D abacus-like cage polymer is obtained as inferred from X-ray diffraction
analysis. This extended solid state structure, cage-<b>2</b>, contains individual zinc dimer cage submits and appears stabilized
by solvent molecules (DMF) and the counteranion (acetate). Rod-like
assemblies are also observed by DLS and SEM. This construct, in contrast
to cage-<b>1</b>, proved fluorescent in mixed organic media.
The structure of the ligand itself (i.e., in the absence of ZnĀ(II))
was confirmed by X-ray crystallographic analysis and was found to
assemble into a supramolecular polymer. Conversion to a dimer form
was seen upon the addition of TBAOAc. On the basis of the metric parameters,
the structures seen in the solid state are stabilized via hydrogen
bonding interactions involving solvent molecules
Self-Assembled Pyridine-Dipyrrolate Cages
An
inherently nonlinear pyridine dipyrrolate ligand, namely 2,6-bisĀ(3,4-diethyl-5-carboxy-1<i>H</i>-pyrrol-2yl)Āpyridine (compound <b>1</b>), is able
to distinguish between different zincĀ(II) cation sources, namely ZnĀ(acac)<sub>2</sub> and ZnĀ(OAc)<sub>2</sub>, respectively. This differentiation
is manifest both in terms of the observed fluorescent behavior in
mixed organic media and the reaction chemistry. Treatment of <b>1</b> with ZnĀ(acac)<sub>2</sub> gives rise to a cage dimer, cage-<b>1</b>, wherein two molecules of compound <b>1</b> act as
double bridging units to connect two individual cage subunits. As
inferred from X-ray crystallographic studies, this cage system consists
of discrete zinc dimers with hydroxide bridges that, with the assistance
of bound DMF solvent molecules, serve to fix the geometry and orientation
of the pyridine dipyrrolate building blocks. When a different zinc
source, ZnĀ(OAc)<sub>2</sub>, is used to carry out an ostensibly similar
complexation reaction with compound <b>1</b>, an acetate-bridged
1D abacus-like cage polymer is obtained as inferred from X-ray diffraction
analysis. This extended solid state structure, cage-<b>2</b>, contains individual zinc dimer cage submits and appears stabilized
by solvent molecules (DMF) and the counteranion (acetate). Rod-like
assemblies are also observed by DLS and SEM. This construct, in contrast
to cage-<b>1</b>, proved fluorescent in mixed organic media.
The structure of the ligand itself (i.e., in the absence of ZnĀ(II))
was confirmed by X-ray crystallographic analysis and was found to
assemble into a supramolecular polymer. Conversion to a dimer form
was seen upon the addition of TBAOAc. On the basis of the metric parameters,
the structures seen in the solid state are stabilized via hydrogen
bonding interactions involving solvent molecules
Expanded Porphyrin-Anion Supramolecular Assemblies: Environmentally Responsive Sensors for Organic Solvents and Anions
Porphyrins
have been used frequently to construct supramolecular
assemblies. In contrast, noncovalent ensembles derived from expanded
porphyrins, larger congeners of naturally occurring tetrapyrrole macrocycles,
are all but unknown. Here we report a series of expanded porphyrin-anion
supramolecular assemblies. These systems display unique environmentally
responsive behavior. Addition of polar organic solvents or common
anions to the ensembles leads to either a visible color change, a
change in the fluorescence emission features, or differences in solubility.
The actual response, which could be followed easily by the naked eye,
was found to depend on the specifics of the assembly, as well as the
choice of analyte. Using the ensembles of this study, it proved possible
to differentiate between common solvents, such as diethyl ether, THF,
ethyl acetate, acetone, alcohol, acetonitrile, DMF, and DMSO, identify
complex solvent systems, as well as distinguish between the fluoride,
chloride, bromide, nitrate, and sulfate anions