Electronic Control of Metal-Centered Chirality in η⁵:κ<i>S</i>‑Indenyl-Sulfanyl and -Sulfinyl Rhodacycles of 2‑Phenylpyridine

Cyclometalation of 2-phenylpyridine with the η⁵:κ<i>S</i>-indenyl-sulfanyl and -sulfinyl rhodium dichloride complexes <i>rac</i>-<b>8</b>, (p<i>R</i>*,<i>R</i>_S*)-<b>9</b>, and (p<i>R</i>*,<i>S</i>_S*)-<b>9</b> in the presence of AgSbF₆ 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>_Rh*)] to the epimer with the phenyl ligand <i>syn</i> to the benzo-ring [(p<i>R</i>*,<i>R</i>_Rh*)] 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>₂ (C₂D₂Cl₄) solution or at 60 °C in C₂D₂Cl₄ 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>_Rh*/<i>R</i>_Rh* 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 ¹³C NMR and X-ray diffraction studies which show greater slip-fold distortions toward η³-coordination of the indenyl ligand in the <i>S</i>_Rh* epimers of the rhodacyclic complexes

Electronic Control of Metal-Centered Chirality in η⁵:κ<i>S</i>‑Indenyl-Sulfanyl and -Sulfinyl Rhodacycles of 2‑Phenylpyridine

Cyclometalation of 2-phenylpyridine with the η⁵:κ<i>S</i>-indenyl-sulfanyl and -sulfinyl rhodium dichloride complexes <i>rac</i>-<b>8</b>, (p<i>R</i>*,<i>R</i>_S*)-<b>9</b>, and (p<i>R</i>*,<i>S</i>_S*)-<b>9</b> in the presence of AgSbF₆ 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>_Rh*)] to the epimer with the phenyl ligand <i>syn</i> to the benzo-ring [(p<i>R</i>*,<i>R</i>_Rh*)] 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>₂ (C₂D₂Cl₄) solution or at 60 °C in C₂D₂Cl₄ 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>_Rh*/<i>R</i>_Rh* 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 ¹³C NMR and X-ray diffraction studies which show greater slip-fold distortions toward η³-coordination of the indenyl ligand in the <i>S</i>_Rh* 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^– over various other anions with concomitant changes in both their UV/visible and fluorescence properties upon Cl^– addition, attributed to initial H-bonding followed by NH deprotonation in the presence of excess Cl^–, 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^– over various other anions with concomitant changes in both their UV/visible and fluorescence properties upon Cl^– addition, attributed to initial H-bonding followed by NH deprotonation in the presence of excess Cl^–, 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 η⁵: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)­naphthalene (<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)­benzene, 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>_S*)-<b>5</b> and (a<i>R</i>*,<i>S</i>_S*)-<b>6</b>, with the relative configuration of <b>5</b> established using single-crystal X-ray diffraction. The dichloro­[η⁵:κ<i>S</i>-indenyl-sulfanyl and -sulfinyl]rhodium complexes <i>rac</i>-<b>4</b>, (p<i>R</i>*,<i>S</i>_S*)-<b>7</b>, and (p<i>R</i>*,<i>R</i>_S*)-<b>8</b> were synthesized through reaction of the ligands <i>rac</i>-<b>3</b>, (a<i>R</i>*,<i>R</i>_S*)-<b>5</b>, and (a<i>R</i>*,<i>S</i>_S*)-<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 ¹H NMR analysis using the chiral shift reagent Eu­(hfc)₃. 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>_S)-<b>8</b>, with the Flack parameter refining to 0.00(2)

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Stereospecific Syntheses and Structures of Planar Chiral Bidentate η⁵: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)­naphthalene (<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)­benzene, 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>_S*)-<b>5</b> and (a<i>R</i>*,<i>S</i>_S*)-<b>6</b>, with the relative configuration of <b>5</b> established using single-crystal X-ray diffraction. The dichloro­[η⁵:κ<i>S</i>-indenyl-sulfanyl and -sulfinyl]rhodium complexes <i>rac</i>-<b>4</b>, (p<i>R</i>*,<i>S</i>_S*)-<b>7</b>, and (p<i>R</i>*,<i>R</i>_S*)-<b>8</b> were synthesized through reaction of the ligands <i>rac</i>-<b>3</b>, (a<i>R</i>*,<i>R</i>_S*)-<b>5</b>, and (a<i>R</i>*,<i>S</i>_S*)-<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 ¹H NMR analysis using the chiral shift reagent Eu­(hfc)₃. 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>_S)-<b>8</b>, with the Flack parameter refining to 0.00(2)

Stereospecific Syntheses and Structures of Planar Chiral Bidentate η⁵: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)­naphthalene (<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)­benzene, 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>_S*)-<b>5</b> and (a<i>R</i>*,<i>S</i>_S*)-<b>6</b>, with the relative configuration of <b>5</b> established using single-crystal X-ray diffraction. The dichloro­[η⁵:κ<i>S</i>-indenyl-sulfanyl and -sulfinyl]rhodium complexes <i>rac</i>-<b>4</b>, (p<i>R</i>*,<i>S</i>_S*)-<b>7</b>, and (p<i>R</i>*,<i>R</i>_S*)-<b>8</b> were synthesized through reaction of the ligands <i>rac</i>-<b>3</b>, (a<i>R</i>*,<i>R</i>_S*)-<b>5</b>, and (a<i>R</i>*,<i>S</i>_S*)-<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 ¹H NMR analysis using the chiral shift reagent Eu­(hfc)₃. 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>_S)-<b>8</b>, with the Flack parameter refining to 0.00(2)

Stereospecific Syntheses and Structures of Planar Chiral Bidentate η⁵: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)­naphthalene (<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)­benzene, 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>_S*)-<b>5</b> and (a<i>R</i>*,<i>S</i>_S*)-<b>6</b>, with the relative configuration of <b>5</b> established using single-crystal X-ray diffraction. The dichloro­[η⁵:κ<i>S</i>-indenyl-sulfanyl and -sulfinyl]rhodium complexes <i>rac</i>-<b>4</b>, (p<i>R</i>*,<i>S</i>_S*)-<b>7</b>, and (p<i>R</i>*,<i>R</i>_S*)-<b>8</b> were synthesized through reaction of the ligands <i>rac</i>-<b>3</b>, (a<i>R</i>*,<i>R</i>_S*)-<b>5</b>, and (a<i>R</i>*,<i>S</i>_S*)-<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 ¹H NMR analysis using the chiral shift reagent Eu­(hfc)₃. 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>_S)-<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 (Zn­(DMF)­NO₃)₂(NDC)­(DPMNI), where NDC = 2,6-naphthalenedicarboxylate and DPMNI = <i>N</i>,<i>N</i>′-bis­(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) Å