13 research outputs found
Electronic Control of Metal-Centered Chirality in η<sup>5</sup>:κ<i>S</i>‑Indenyl-Sulfanyl and -Sulfinyl Rhodacycles of 2‑Phenylpyridine
Cyclometalation of 2-phenylpyridine
with the η<sup>5</sup>:κ<i>S</i>-indenyl-sulfanyl
and -sulfinyl rhodium
dichloride complexes <i>rac</i>-<b>8</b>, (p<i>R</i>*,<i>R</i><sub>S</sub>*)-<b>9</b>, and
(p<i>R</i>*,<i>S</i><sub>S</sub>*)-<b>9</b> in the presence of AgSbF<sub>6</sub> provided the rhodacyclic complexes <b>10</b>, <b>11</b>, and <b>12</b>, respectively, in
yields ranging from 72% to 92%. The complexes were obtained as mixtures
of chiral-at-metal epimers, with ratios of the epimer with the phenyl
ligand <i>anti</i> to the indenyl benzo-ring [(p<i>R</i>*,<i>S</i><sub>Rh</sub>*)] to the epimer with
the phenyl ligand <i>syn</i> to the benzo-ring [(p<i>R</i>*,<i>R</i><sub>Rh</sub>*)] of 3:2, 10:1, and
2:5 for complexes <b>10</b>, <b>11</b>, and <b>12</b>, respectively, establishing that sulfoxide chirality has a significant
role in stereocontrol of metal-centered chirality in the initially
formed complexes. Equilibration of the rhodacyclic complexes takes
place at 120 °C in 1,1,2,2-tetrachloroethane-<i>d</i><sub>2</sub> (C<sub>2</sub>D<sub>2</sub>Cl<sub>4</sub>) solution
or at 60 °C in C<sub>2</sub>D<sub>2</sub>Cl<sub>4</sub> solution
in the presence of catalytic 4-ethylpyridine. Kinetic studies demonstrate
that under the former conditions, epimerization is catalyzed by adventitious
water and that epimerization occurs through an associative activation
mechanism. The thermodynamic ratios for the <i>S</i><sub>Rh</sub>*/<i>R</i><sub>Rh</sub>* epimers of the complexes
were >100:1, >100:1, and 25:1 for complexes <b>10</b>, <b>11</b>, and <b>12</b>, respectively, consistent with a structural
indenyl effect favoring the epimer where the stronger structural trans
effect phenyl ligand is <i>anti</i> to the indenyl benzo-ring.
This is supported by <sup>13</sup>C NMR and X-ray diffraction studies
which show greater slip-fold distortions toward η<sup>3</sup>-coordination of the indenyl ligand in the <i>S</i><sub>Rh</sub>* epimers of the rhodacyclic complexes
Electronic Control of Metal-Centered Chirality in η<sup>5</sup>:κ<i>S</i>‑Indenyl-Sulfanyl and -Sulfinyl Rhodacycles of 2‑Phenylpyridine
Cyclometalation of 2-phenylpyridine
with the η<sup>5</sup>:κ<i>S</i>-indenyl-sulfanyl
and -sulfinyl rhodium
dichloride complexes <i>rac</i>-<b>8</b>, (p<i>R</i>*,<i>R</i><sub>S</sub>*)-<b>9</b>, and
(p<i>R</i>*,<i>S</i><sub>S</sub>*)-<b>9</b> in the presence of AgSbF<sub>6</sub> provided the rhodacyclic complexes <b>10</b>, <b>11</b>, and <b>12</b>, respectively, in
yields ranging from 72% to 92%. The complexes were obtained as mixtures
of chiral-at-metal epimers, with ratios of the epimer with the phenyl
ligand <i>anti</i> to the indenyl benzo-ring [(p<i>R</i>*,<i>S</i><sub>Rh</sub>*)] to the epimer with
the phenyl ligand <i>syn</i> to the benzo-ring [(p<i>R</i>*,<i>R</i><sub>Rh</sub>*)] of 3:2, 10:1, and
2:5 for complexes <b>10</b>, <b>11</b>, and <b>12</b>, respectively, establishing that sulfoxide chirality has a significant
role in stereocontrol of metal-centered chirality in the initially
formed complexes. Equilibration of the rhodacyclic complexes takes
place at 120 °C in 1,1,2,2-tetrachloroethane-<i>d</i><sub>2</sub> (C<sub>2</sub>D<sub>2</sub>Cl<sub>4</sub>) solution
or at 60 °C in C<sub>2</sub>D<sub>2</sub>Cl<sub>4</sub> solution
in the presence of catalytic 4-ethylpyridine. Kinetic studies demonstrate
that under the former conditions, epimerization is catalyzed by adventitious
water and that epimerization occurs through an associative activation
mechanism. The thermodynamic ratios for the <i>S</i><sub>Rh</sub>*/<i>R</i><sub>Rh</sub>* epimers of the complexes
were >100:1, >100:1, and 25:1 for complexes <b>10</b>, <b>11</b>, and <b>12</b>, respectively, consistent with a structural
indenyl effect favoring the epimer where the stronger structural trans
effect phenyl ligand is <i>anti</i> to the indenyl benzo-ring.
This is supported by <sup>13</sup>C NMR and X-ray diffraction studies
which show greater slip-fold distortions toward η<sup>3</sup>-coordination of the indenyl ligand in the <i>S</i><sub>Rh</sub>* epimers of the rhodacyclic complexes
Colorimetric and Luminescent Sensors for Chloride: Hydrogen Bonding vs Deprotonation
The synthesis and photophysical properties of four squaramide based fluorescent anion sensors (<b>1</b>–<b>4</b>) are described. These luminescent compounds showed selectivity for Cl<sup>–</sup> over various other anions with concomitant changes in both their UV/visible and fluorescence properties upon Cl<sup>–</sup> addition, attributed to initial H-bonding followed by NH deprotonation in the presence of excess Cl<sup>–</sup>, signaled by a color change. The nature of the electron withdrawing aryl substituents is directly related to the H-bonding ability/acidity of the squaramide protons and can be used to tune the deprotonation behavior
Colorimetric and Luminescent Sensors for Chloride: Hydrogen Bonding vs Deprotonation
The synthesis and photophysical properties of four squaramide based fluorescent anion sensors (<b>1</b>–<b>4</b>) are described. These luminescent compounds showed selectivity for Cl<sup>–</sup> over various other anions with concomitant changes in both their UV/visible and fluorescence properties upon Cl<sup>–</sup> addition, attributed to initial H-bonding followed by NH deprotonation in the presence of excess Cl<sup>–</sup>, signaled by a color change. The nature of the electron withdrawing aryl substituents is directly related to the H-bonding ability/acidity of the squaramide protons and can be used to tune the deprotonation behavior
Stereospecific Syntheses and Structures of Planar Chiral Bidentate η<sup>5</sup>:κ<i>S</i><b>-</b>Indenyl<b>-</b>Sulfanyl and <b>-</b>Sulfinyl Complexes of Rhodium(III)
Axially chiral <i>rac</i>-1-(2-methyl-1<i>H</i>-inden-3-yl)-2-(methylsulfanyl)Ânaphthalene (<i>rac</i>-<b>3</b>) was synthesized from methyl 2-(methylsulfanyl)-1-naphthoate
through reaction with the di-Grignard reagent derived from 1-bromo-2-(2-bromopropyl)Âbenzene,
followed by acid-catalyzed dehydration of the intermediate indanol.
Oxidation of <i>rac</i>-<b>3</b> with <i>m</i>-CPBA gave the diastereomeric sulfoxides (a<i>R</i>*,<i>R</i><sub>S</sub>*)-<b>5</b> and (a<i>R</i>*,<i>S</i><sub>S</sub>*)-<b>6</b>, with the relative configuration
of <b>5</b> established using single-crystal X-ray diffraction.
The dichloroÂ[η<sup>5</sup>:Îş<i>S</i>-indenyl-sulfanyl
and -sulfinyl]rhodium complexes <i>rac</i>-<b>4</b>, (p<i>R</i>*,<i>S</i><sub>S</sub>*)-<b>7</b>, and (p<i>R</i>*,<i>R</i><sub>S</sub>*)-<b>8</b> were synthesized through reaction of the ligands <i>rac</i>-<b>3</b>, (a<i>R</i>*,<i>R</i><sub>S</sub>*)-<b>5</b>, and (a<i>R</i>*,<i>S</i><sub>S</sub>*)-<b>6</b>, respectively, with rhodium
trichloride in 9:1 methanol/water solution heated under reflux. The
use of water as a cosolvent was found to be critical for obtaining
good yields in the complexation reactions. Solid-state structures
for the racemic rhodium complexes were determined through single-crystal
X-ray diffraction. The enantiomers of the ligands <b>3</b>, <b>5</b>, and <b>6</b> were obtained in high enantiopurity
through subjecting <i>rac</i>-<b>3</b> to a series
of Kagan asymmetric sulfoxidation, deoxygenation, and resulfoxidation
reactions. The enantiomeric relationship of the rhodium complexes
derived from the enantio-enriched ligands was confirmed by CD spectroscopy,
and the high enantiopurity of the complexes established by <sup>1</sup>H NMR analysis using the chiral shift reagent EuÂ(hfc)<sub>3</sub>. The absolute configurations of the nonracemic ligands and rhodium
complexes were established by a single-crystal X-ray diffraction determination
of the solid-state structure of (p<i>S</i>,<i>S</i><sub>S</sub>)-<b>8</b>, with the Flack parameter refining to
0.00(2)
Shale gas resources of the Bowland Basin, NW England: a holistic study
Detailed correlation of Cuadrilla's exploration borehole core
Stereospecific Syntheses and Structures of Planar Chiral Bidentate η<sup>5</sup>:κ<i>S</i><b>-</b>Indenyl<b>-</b>Sulfanyl and <b>-</b>Sulfinyl Complexes of Rhodium(III)
Axially chiral <i>rac</i>-1-(2-methyl-1<i>H</i>-inden-3-yl)-2-(methylsulfanyl)Ânaphthalene (<i>rac</i>-<b>3</b>) was synthesized from methyl 2-(methylsulfanyl)-1-naphthoate
through reaction with the di-Grignard reagent derived from 1-bromo-2-(2-bromopropyl)Âbenzene,
followed by acid-catalyzed dehydration of the intermediate indanol.
Oxidation of <i>rac</i>-<b>3</b> with <i>m</i>-CPBA gave the diastereomeric sulfoxides (a<i>R</i>*,<i>R</i><sub>S</sub>*)-<b>5</b> and (a<i>R</i>*,<i>S</i><sub>S</sub>*)-<b>6</b>, with the relative configuration
of <b>5</b> established using single-crystal X-ray diffraction.
The dichloroÂ[η<sup>5</sup>:Îş<i>S</i>-indenyl-sulfanyl
and -sulfinyl]rhodium complexes <i>rac</i>-<b>4</b>, (p<i>R</i>*,<i>S</i><sub>S</sub>*)-<b>7</b>, and (p<i>R</i>*,<i>R</i><sub>S</sub>*)-<b>8</b> were synthesized through reaction of the ligands <i>rac</i>-<b>3</b>, (a<i>R</i>*,<i>R</i><sub>S</sub>*)-<b>5</b>, and (a<i>R</i>*,<i>S</i><sub>S</sub>*)-<b>6</b>, respectively, with rhodium
trichloride in 9:1 methanol/water solution heated under reflux. The
use of water as a cosolvent was found to be critical for obtaining
good yields in the complexation reactions. Solid-state structures
for the racemic rhodium complexes were determined through single-crystal
X-ray diffraction. The enantiomers of the ligands <b>3</b>, <b>5</b>, and <b>6</b> were obtained in high enantiopurity
through subjecting <i>rac</i>-<b>3</b> to a series
of Kagan asymmetric sulfoxidation, deoxygenation, and resulfoxidation
reactions. The enantiomeric relationship of the rhodium complexes
derived from the enantio-enriched ligands was confirmed by CD spectroscopy,
and the high enantiopurity of the complexes established by <sup>1</sup>H NMR analysis using the chiral shift reagent EuÂ(hfc)<sub>3</sub>. The absolute configurations of the nonracemic ligands and rhodium
complexes were established by a single-crystal X-ray diffraction determination
of the solid-state structure of (p<i>S</i>,<i>S</i><sub>S</sub>)-<b>8</b>, with the Flack parameter refining to
0.00(2)
Stereospecific Syntheses and Structures of Planar Chiral Bidentate η<sup>5</sup>:κ<i>S</i><b>-</b>Indenyl<b>-</b>Sulfanyl and <b>-</b>Sulfinyl Complexes of Rhodium(III)
Axially chiral <i>rac</i>-1-(2-methyl-1<i>H</i>-inden-3-yl)-2-(methylsulfanyl)Ânaphthalene (<i>rac</i>-<b>3</b>) was synthesized from methyl 2-(methylsulfanyl)-1-naphthoate
through reaction with the di-Grignard reagent derived from 1-bromo-2-(2-bromopropyl)Âbenzene,
followed by acid-catalyzed dehydration of the intermediate indanol.
Oxidation of <i>rac</i>-<b>3</b> with <i>m</i>-CPBA gave the diastereomeric sulfoxides (a<i>R</i>*,<i>R</i><sub>S</sub>*)-<b>5</b> and (a<i>R</i>*,<i>S</i><sub>S</sub>*)-<b>6</b>, with the relative configuration
of <b>5</b> established using single-crystal X-ray diffraction.
The dichloroÂ[η<sup>5</sup>:Îş<i>S</i>-indenyl-sulfanyl
and -sulfinyl]rhodium complexes <i>rac</i>-<b>4</b>, (p<i>R</i>*,<i>S</i><sub>S</sub>*)-<b>7</b>, and (p<i>R</i>*,<i>R</i><sub>S</sub>*)-<b>8</b> were synthesized through reaction of the ligands <i>rac</i>-<b>3</b>, (a<i>R</i>*,<i>R</i><sub>S</sub>*)-<b>5</b>, and (a<i>R</i>*,<i>S</i><sub>S</sub>*)-<b>6</b>, respectively, with rhodium
trichloride in 9:1 methanol/water solution heated under reflux. The
use of water as a cosolvent was found to be critical for obtaining
good yields in the complexation reactions. Solid-state structures
for the racemic rhodium complexes were determined through single-crystal
X-ray diffraction. The enantiomers of the ligands <b>3</b>, <b>5</b>, and <b>6</b> were obtained in high enantiopurity
through subjecting <i>rac</i>-<b>3</b> to a series
of Kagan asymmetric sulfoxidation, deoxygenation, and resulfoxidation
reactions. The enantiomeric relationship of the rhodium complexes
derived from the enantio-enriched ligands was confirmed by CD spectroscopy,
and the high enantiopurity of the complexes established by <sup>1</sup>H NMR analysis using the chiral shift reagent EuÂ(hfc)<sub>3</sub>. The absolute configurations of the nonracemic ligands and rhodium
complexes were established by a single-crystal X-ray diffraction determination
of the solid-state structure of (p<i>S</i>,<i>S</i><sub>S</sub>)-<b>8</b>, with the Flack parameter refining to
0.00(2)
Stereospecific Syntheses and Structures of Planar Chiral Bidentate η<sup>5</sup>:κ<i>S</i><b>-</b>Indenyl<b>-</b>Sulfanyl and <b>-</b>Sulfinyl Complexes of Rhodium(III)
Axially chiral <i>rac</i>-1-(2-methyl-1<i>H</i>-inden-3-yl)-2-(methylsulfanyl)Ânaphthalene (<i>rac</i>-<b>3</b>) was synthesized from methyl 2-(methylsulfanyl)-1-naphthoate
through reaction with the di-Grignard reagent derived from 1-bromo-2-(2-bromopropyl)Âbenzene,
followed by acid-catalyzed dehydration of the intermediate indanol.
Oxidation of <i>rac</i>-<b>3</b> with <i>m</i>-CPBA gave the diastereomeric sulfoxides (a<i>R</i>*,<i>R</i><sub>S</sub>*)-<b>5</b> and (a<i>R</i>*,<i>S</i><sub>S</sub>*)-<b>6</b>, with the relative configuration
of <b>5</b> established using single-crystal X-ray diffraction.
The dichloroÂ[η<sup>5</sup>:Îş<i>S</i>-indenyl-sulfanyl
and -sulfinyl]rhodium complexes <i>rac</i>-<b>4</b>, (p<i>R</i>*,<i>S</i><sub>S</sub>*)-<b>7</b>, and (p<i>R</i>*,<i>R</i><sub>S</sub>*)-<b>8</b> were synthesized through reaction of the ligands <i>rac</i>-<b>3</b>, (a<i>R</i>*,<i>R</i><sub>S</sub>*)-<b>5</b>, and (a<i>R</i>*,<i>S</i><sub>S</sub>*)-<b>6</b>, respectively, with rhodium
trichloride in 9:1 methanol/water solution heated under reflux. The
use of water as a cosolvent was found to be critical for obtaining
good yields in the complexation reactions. Solid-state structures
for the racemic rhodium complexes were determined through single-crystal
X-ray diffraction. The enantiomers of the ligands <b>3</b>, <b>5</b>, and <b>6</b> were obtained in high enantiopurity
through subjecting <i>rac</i>-<b>3</b> to a series
of Kagan asymmetric sulfoxidation, deoxygenation, and resulfoxidation
reactions. The enantiomeric relationship of the rhodium complexes
derived from the enantio-enriched ligands was confirmed by CD spectroscopy,
and the high enantiopurity of the complexes established by <sup>1</sup>H NMR analysis using the chiral shift reagent EuÂ(hfc)<sub>3</sub>. The absolute configurations of the nonracemic ligands and rhodium
complexes were established by a single-crystal X-ray diffraction determination
of the solid-state structure of (p<i>S</i>,<i>S</i><sub>S</sub>)-<b>8</b>, with the Flack parameter refining to
0.00(2)
Electronic, Optical, and Computational Studies of a Redox-Active Napthalenediimide-Based Coordination Polymer
The new one-dimensional coordination
framework (ZnÂ(DMF)ÂNO<sub>3</sub>)<sub>2</sub>(NDC)Â(DPMNI), where NDC
= 2,6-naphthalenedicarboxylate
and DPMNI = <i>N</i>,<i>N</i>′-bisÂ(4-pyridylmethyl)-1,4,5,8-naphthalenetetracarboxydiimide,
which has been crystallographically characterized, exhibits two redox-accessible
states due to the successive reduction of the naphthalenediimide (NDI)
ligand core. Solid-state electrochemical and vis–near-IR spectroelectrochemical
measurements coupled with density functional theory (DFT) calculations
enabled the origins of the optical transitions in the spectra of the
monoradical anion and dianion states of the material to be assigned.
Electron paramagnetic resonance (EPR) spectroscopy revealed that the
paramagnetic radical anion state of the DPMNI core could be accessed
upon broad-spectrum white light irradiation of the material, revealing
a long-lived excited state, possibly stabilized by charge delocalization
which arises from extensive π<i>–</i>π*
stacking interactions between alternating NDC and NDI aromatic cores
which are separated by a distance of 3.580(2) Ă…