9 research outputs found
Induction and Rationalization of Supramolecular Chirality in the Tweezer–Diamine Complexes: Insights from Experimental and DFT Studies
A series of supramolecular chiral
1:1 sandwich complexes (<b>1</b><sub>M</sub>·L and <b>2</b><sub>M</sub>·L) consisting of diphenylether/ethane bridged
metallobisporphyrin host (<b>1</b><sub>M</sub> and <b>2</b><sub>M</sub>; M: Zn/Mg) and chiral diamine guest (L) have been presented.
The host–guest complexes are compared just upon changing the
metal ion (Mg vs Zn) or the bridge (highly flexible ethane vs rigid
diphenylether) keeping other factors similar. The factors that would
influence the chirality induction process along with their contributions
toward the sign and intensity of the CD couplet of the overall complex
have been analyzed. Larger CD amplitude was observed in the host–guest
complex with the more flexible ethane bridge as compared to the rigid
diphenylether bridged one, irrespective of the metal ion used. Also,
Zn complexes have displayed larger CD amplitude because of their stronger
binding with the chiral diamines. A fairly linear dependence between
the binding constant (<i>K</i>) and CD amplitude has been
observed. Moreover, the amplitude of the CD couplet has been correlated
with the relative steric bulk of the substituent at the stereogenic
center: with increasing the bulk, CD intensity gradually increases.
However, large increase of steric hindrance, after a threshold value,
has diminished the intensity. The observation of a weak positive CD
couplet between (1<i>R</i>,2<i>R</i>)-DPEA guest
and Zn-bisporphyrin hosts indicates that the clockwise-twisted (steric-controlled)
conformer is more populated as compared to the anticlockwise (chirality-controlled)
one. In contrast, amplitude of the positive CD couplets is larger
with Mg-bisporphyrin hosts, suggesting almost exclusive contribution
of the clockwise-twisted conformer guided solely by sterics. DFT calculations
support the experimental observations and have displayed the possible
interconversion between clockwise and anticlockwise twisted conformers
just upon changing the bulk of the substituent irrespective of the
nature of chirality at the stereogenic center
Induction and Rationalization of Supramolecular Chirality in the Tweezer–Diamine Complexes: Insights from Experimental and DFT Studies
A series of supramolecular chiral
1:1 sandwich complexes (<b>1</b><sub>M</sub>·L and <b>2</b><sub>M</sub>·L) consisting of diphenylether/ethane bridged
metallobisporphyrin host (<b>1</b><sub>M</sub> and <b>2</b><sub>M</sub>; M: Zn/Mg) and chiral diamine guest (L) have been presented.
The host–guest complexes are compared just upon changing the
metal ion (Mg vs Zn) or the bridge (highly flexible ethane vs rigid
diphenylether) keeping other factors similar. The factors that would
influence the chirality induction process along with their contributions
toward the sign and intensity of the CD couplet of the overall complex
have been analyzed. Larger CD amplitude was observed in the host–guest
complex with the more flexible ethane bridge as compared to the rigid
diphenylether bridged one, irrespective of the metal ion used. Also,
Zn complexes have displayed larger CD amplitude because of their stronger
binding with the chiral diamines. A fairly linear dependence between
the binding constant (<i>K</i>) and CD amplitude has been
observed. Moreover, the amplitude of the CD couplet has been correlated
with the relative steric bulk of the substituent at the stereogenic
center: with increasing the bulk, CD intensity gradually increases.
However, large increase of steric hindrance, after a threshold value,
has diminished the intensity. The observation of a weak positive CD
couplet between (1<i>R</i>,2<i>R</i>)-DPEA guest
and Zn-bisporphyrin hosts indicates that the clockwise-twisted (steric-controlled)
conformer is more populated as compared to the anticlockwise (chirality-controlled)
one. In contrast, amplitude of the positive CD couplets is larger
with Mg-bisporphyrin hosts, suggesting almost exclusive contribution
of the clockwise-twisted conformer guided solely by sterics. DFT calculations
support the experimental observations and have displayed the possible
interconversion between clockwise and anticlockwise twisted conformers
just upon changing the bulk of the substituent irrespective of the
nature of chirality at the stereogenic center
Induction and Rationalization of Supramolecular Chirality in the Tweezer–Diamine Complexes: Insights from Experimental and DFT Studies
A series of supramolecular chiral
1:1 sandwich complexes (<b>1</b><sub>M</sub>·L and <b>2</b><sub>M</sub>·L) consisting of diphenylether/ethane bridged
metallobisporphyrin host (<b>1</b><sub>M</sub> and <b>2</b><sub>M</sub>; M: Zn/Mg) and chiral diamine guest (L) have been presented.
The host–guest complexes are compared just upon changing the
metal ion (Mg vs Zn) or the bridge (highly flexible ethane vs rigid
diphenylether) keeping other factors similar. The factors that would
influence the chirality induction process along with their contributions
toward the sign and intensity of the CD couplet of the overall complex
have been analyzed. Larger CD amplitude was observed in the host–guest
complex with the more flexible ethane bridge as compared to the rigid
diphenylether bridged one, irrespective of the metal ion used. Also,
Zn complexes have displayed larger CD amplitude because of their stronger
binding with the chiral diamines. A fairly linear dependence between
the binding constant (<i>K</i>) and CD amplitude has been
observed. Moreover, the amplitude of the CD couplet has been correlated
with the relative steric bulk of the substituent at the stereogenic
center: with increasing the bulk, CD intensity gradually increases.
However, large increase of steric hindrance, after a threshold value,
has diminished the intensity. The observation of a weak positive CD
couplet between (1<i>R</i>,2<i>R</i>)-DPEA guest
and Zn-bisporphyrin hosts indicates that the clockwise-twisted (steric-controlled)
conformer is more populated as compared to the anticlockwise (chirality-controlled)
one. In contrast, amplitude of the positive CD couplets is larger
with Mg-bisporphyrin hosts, suggesting almost exclusive contribution
of the clockwise-twisted conformer guided solely by sterics. DFT calculations
support the experimental observations and have displayed the possible
interconversion between clockwise and anticlockwise twisted conformers
just upon changing the bulk of the substituent irrespective of the
nature of chirality at the stereogenic center
A Nonempirical Approach for Direct Determination of the Absolute Configuration of 1,2-Diols and Amino Alcohols Using Mg(II)bisporphyrin
We
report here a simple, facile, and direct nonempirical protocol
for determining the absolute stereochemistry of a variety of chiral
1,2-diols and amino alcohols at room temperature with no chemical
derivatization using Mg(II)bisporphyrin as a host. Addition of excess
substrates resulted in the formation of a 1:2 host–guest complex
in which two substrates bind in an unusual <i>endo-endo</i> fashion because of interligand H-bonding within the bisporphyrin
cavity leading to the formation of a unidirectional screw in the bisporphyrin
moiety that allowed us an accurate absolute stereochemical determination
of the chiral substrate via exciton-coupled circular dichroism (ECCD).
The sign of the CD couplet has also been found to be inverted when
the stereogenic center is moved by one C atom simply from the bound
to an unbound functionality and thus able to discriminate between
them successfully. Strong complexation of the alcoholic oxygen with
Mg(II)bisporphyrin rigidifies the host–guest complex, which
eventually enhances its ability to stereochemically differentiate
the asymmetric center. The ECCD sign of a large number of substrates
has followed consistent and predictable trends; thus, the system is
widely applicable. Moreover, computational calculations clearly support
the experimental observations along with the absolute stereochemistry
of the chiral substrate
A Nonempirical Approach for Direct Determination of the Absolute Configuration of 1,2-Diols and Amino Alcohols Using Mg(II)bisporphyrin
We
report here a simple, facile, and direct nonempirical protocol
for determining the absolute stereochemistry of a variety of chiral
1,2-diols and amino alcohols at room temperature with no chemical
derivatization using Mg(II)bisporphyrin as a host. Addition of excess
substrates resulted in the formation of a 1:2 host–guest complex
in which two substrates bind in an unusual <i>endo-endo</i> fashion because of interligand H-bonding within the bisporphyrin
cavity leading to the formation of a unidirectional screw in the bisporphyrin
moiety that allowed us an accurate absolute stereochemical determination
of the chiral substrate via exciton-coupled circular dichroism (ECCD).
The sign of the CD couplet has also been found to be inverted when
the stereogenic center is moved by one C atom simply from the bound
to an unbound functionality and thus able to discriminate between
them successfully. Strong complexation of the alcoholic oxygen with
Mg(II)bisporphyrin rigidifies the host–guest complex, which
eventually enhances its ability to stereochemically differentiate
the asymmetric center. The ECCD sign of a large number of substrates
has followed consistent and predictable trends; thus, the system is
widely applicable. Moreover, computational calculations clearly support
the experimental observations along with the absolute stereochemistry
of the chiral substrate
A Nonempirical Approach for Direct Determination of the Absolute Configuration of 1,2-Diols and Amino Alcohols Using Mg(II)bisporphyrin
We
report here a simple, facile, and direct nonempirical protocol
for determining the absolute stereochemistry of a variety of chiral
1,2-diols and amino alcohols at room temperature with no chemical
derivatization using Mg(II)bisporphyrin as a host. Addition of excess
substrates resulted in the formation of a 1:2 host–guest complex
in which two substrates bind in an unusual <i>endo-endo</i> fashion because of interligand H-bonding within the bisporphyrin
cavity leading to the formation of a unidirectional screw in the bisporphyrin
moiety that allowed us an accurate absolute stereochemical determination
of the chiral substrate via exciton-coupled circular dichroism (ECCD).
The sign of the CD couplet has also been found to be inverted when
the stereogenic center is moved by one C atom simply from the bound
to an unbound functionality and thus able to discriminate between
them successfully. Strong complexation of the alcoholic oxygen with
Mg(II)bisporphyrin rigidifies the host–guest complex, which
eventually enhances its ability to stereochemically differentiate
the asymmetric center. The ECCD sign of a large number of substrates
has followed consistent and predictable trends; thus, the system is
widely applicable. Moreover, computational calculations clearly support
the experimental observations along with the absolute stereochemistry
of the chiral substrate
Highly Enhanced Bisignate Circular Dichroism of Ferrocene-Bridged Zn(II) Bisporphyrin <i>Tweezer</i> with Extended Chiral Substrates due to Well-Matched Host–Guest System
Four
new chiral <i>tweezer-</i>diamine complexes, consisting
of an achiral ferrocene-bridged Zn(II)bisporhyrin host (<b>1</b>) and two small diamines (1<i>R</i>,2<i>R</i>)-1,2-diphenylethylene diamine {(1<i>R</i>,2<i>R</i>)-DPEA} and (1<i>S</i>,2<i>S</i>)-1,2-cyclohexane
diamine {(1<i>S</i>,2<i>S</i>)-CHDA} and two extended
diamines (1<i>R</i>,2<i>R</i>)-<i>N</i>,<i>N</i>′-bis-(isonicotinoyl)-1,2-diphenylethylene
diamine {(1<i>R</i>,2<i>R</i>)-DPEApy} and (1<i>S</i>,2<i>S</i>)-<i>N</i>,<i>N</i>′-bis-(isonicotinoyl)-1,2-cyclohexane diamine {(1<i>S</i>,2<i>S</i>)-CHDApy} chiral guests, are reported. Additions
of (1<i>R</i>,2<i>R</i>)-DPEA and (1<i>S</i>,2<i>S</i>)-CHDA separately to <b>1</b> in dichloromethane
result in the formation of 1:1 sandwich complexes <b>1·</b>DPEA<sub>(<i>R</i>,<i>R</i>)</sub> and <b>1·</b>CHDA<sub>(<i>S</i>,<i>S</i>)</sub>, respectively, at low guest concentration and 1:2 anti complexes <b>1·</b>(DPEA<sub>(<i>R</i>,<i>R</i>)</sub>)<sub>2</sub> and <b>1·</b>(CHDA<sub>(<i>S</i>,<i>S</i>)</sub>)<sub>2</sub>, respectively, at higher
guest concentration. In contrast, separate additions of (1<i>R</i>,2<i>R</i>)-DPEApy and (1<i>S</i>,2<i>S</i>)-CHDApy to <b>1</b> produce only 1:1 sandwich complexes
of <b>1·</b>DPEApy<sub>(<i>R</i>,<i>R</i>)</sub> and <b>1·</b>CHDApy<sub>(<i>S</i>,<i>S</i>)</sub>, respectively. The binding constants at 295 K between <b>1</b> and (1<i>R</i>,2<i>R</i>)-DPEA are observed
to be (4.7 ± 0.2) × 10<sup>4</sup> M<sup>–1</sup> and (4.3 ± 0.3) × 10<sup>3</sup> M<sup>–1</sup> for 1:1 sandwich and 1:2 anti form, respectively, while the respective
values with (1<i>S</i>,2<i>S</i>)-CHDA are (1.5
± 0.2) × 10<sup>5</sup> M<sup>–1</sup> and (5.9 ±
0.3) × 10<sup>3</sup> M<sup>–1</sup>. However, much larger
values of (2.5 ± 0.3) × 10<sup>5</sup> M<sup>–1</sup> and (1.3 ± 0.3) × 10<sup>6</sup> M<sup>–1</sup> have been observed with DPEApy<sub>(<i>R</i>,<i>R</i>)</sub> and CHDApy<sub>(<i>S</i>,<i>S</i>)</sub>, respectively, to produce the corresponding 1:1 sandwich complexes. <b>1·</b>DPEApy<sub>(<i>R</i>,<i>R</i>)</sub> (<i>A</i><sub>cal</sub>, −1759 cm<sup>–1</sup> M<sup>–1</sup>) (<i>A</i><sub>cal</sub> = Δε<sub>1</sub> – Δε<sub>2</sub>, representing the total
amplitude of the calculated circular dichroism (CD) couplets) shows
∼10-fold increase in CD amplitude compared to the values observed
for <b>1·</b>DPEA<sub>(<i>R</i>,<i>R</i>)</sub> (<i>A</i><sub>cal</sub>, +187 cm<sup>–1</sup> M<sup>–1</sup>), while <b>1·</b>CHDApy<sub>(<i>S</i>,<i>S</i>)</sub> (<i>A</i><sub>cal</sub>, +1886 cm<sup>–1</sup> M<sup>–1</sup>) shows nearly
3-fold increase of the CD amplitude compared to the value observed
for <b>1·</b>CHDA<sub>(<i>S</i>,<i>S</i>)</sub> (<i>A</i><sub>cal</sub>, −785 cm<sup>–1</sup> M<sup>–1</sup>) at 295 K. The <i>A</i><sub>cal</sub> values of −1759 cm<sup>–1</sup> M<sup>–1</sup> and +1886 cm<sup>–1</sup> M<sup>–1</sup> observed
for the <b>1·</b>DPEApy<sub>(<i>R</i>,<i>R</i>)</sub> and <b>1·</b>CHDApy<sub>(<i>S</i>,<i>S</i>)</sub>, respectively, are extremely high. To
the best of our knowledge, these are some of the largest values reported
for a chirality induction process involving bisporphyrin <i>tweezer</i> receptors. The large enhancement in the CD signal intensity is due
to the well complementarity size between Zn(II)bisporphyrin host and
the extended chiral diamines guest, which results large unidirectional
twisting of two porphyrin units to accommodate the guests having preorganized
binding sites with minimum host–guest steric interactions.
It is interesting to note that <b>1·</b>DPEA<sub>(<i>R</i>,<i>R</i>)</sub> and <b>1·</b>DPEApy<sub>(<i>R</i>,<i>R</i>)</sub> show CD signal opposite
in sign to each other, which happens to be the case between <b>1·</b>CHDA<sub>(<i>S</i>,<i>S</i>)</sub> and <b>1·</b>CHDApy<sub>(<i>S</i>,<i>S</i>)</sub> also
Highly Enhanced Bisignate Circular Dichroism of Ferrocene-Bridged Zn(II) Bisporphyrin <i>Tweezer</i> with Extended Chiral Substrates due to Well-Matched Host–Guest System
Four
new chiral <i>tweezer-</i>diamine complexes, consisting
of an achiral ferrocene-bridged Zn(II)bisporhyrin host (<b>1</b>) and two small diamines (1<i>R</i>,2<i>R</i>)-1,2-diphenylethylene diamine {(1<i>R</i>,2<i>R</i>)-DPEA} and (1<i>S</i>,2<i>S</i>)-1,2-cyclohexane
diamine {(1<i>S</i>,2<i>S</i>)-CHDA} and two extended
diamines (1<i>R</i>,2<i>R</i>)-<i>N</i>,<i>N</i>′-bis-(isonicotinoyl)-1,2-diphenylethylene
diamine {(1<i>R</i>,2<i>R</i>)-DPEApy} and (1<i>S</i>,2<i>S</i>)-<i>N</i>,<i>N</i>′-bis-(isonicotinoyl)-1,2-cyclohexane diamine {(1<i>S</i>,2<i>S</i>)-CHDApy} chiral guests, are reported. Additions
of (1<i>R</i>,2<i>R</i>)-DPEA and (1<i>S</i>,2<i>S</i>)-CHDA separately to <b>1</b> in dichloromethane
result in the formation of 1:1 sandwich complexes <b>1·</b>DPEA<sub>(<i>R</i>,<i>R</i>)</sub> and <b>1·</b>CHDA<sub>(<i>S</i>,<i>S</i>)</sub>, respectively, at low guest concentration and 1:2 anti complexes <b>1·</b>(DPEA<sub>(<i>R</i>,<i>R</i>)</sub>)<sub>2</sub> and <b>1·</b>(CHDA<sub>(<i>S</i>,<i>S</i>)</sub>)<sub>2</sub>, respectively, at higher
guest concentration. In contrast, separate additions of (1<i>R</i>,2<i>R</i>)-DPEApy and (1<i>S</i>,2<i>S</i>)-CHDApy to <b>1</b> produce only 1:1 sandwich complexes
of <b>1·</b>DPEApy<sub>(<i>R</i>,<i>R</i>)</sub> and <b>1·</b>CHDApy<sub>(<i>S</i>,<i>S</i>)</sub>, respectively. The binding constants at 295 K between <b>1</b> and (1<i>R</i>,2<i>R</i>)-DPEA are observed
to be (4.7 ± 0.2) × 10<sup>4</sup> M<sup>–1</sup> and (4.3 ± 0.3) × 10<sup>3</sup> M<sup>–1</sup> for 1:1 sandwich and 1:2 anti form, respectively, while the respective
values with (1<i>S</i>,2<i>S</i>)-CHDA are (1.5
± 0.2) × 10<sup>5</sup> M<sup>–1</sup> and (5.9 ±
0.3) × 10<sup>3</sup> M<sup>–1</sup>. However, much larger
values of (2.5 ± 0.3) × 10<sup>5</sup> M<sup>–1</sup> and (1.3 ± 0.3) × 10<sup>6</sup> M<sup>–1</sup> have been observed with DPEApy<sub>(<i>R</i>,<i>R</i>)</sub> and CHDApy<sub>(<i>S</i>,<i>S</i>)</sub>, respectively, to produce the corresponding 1:1 sandwich complexes. <b>1·</b>DPEApy<sub>(<i>R</i>,<i>R</i>)</sub> (<i>A</i><sub>cal</sub>, −1759 cm<sup>–1</sup> M<sup>–1</sup>) (<i>A</i><sub>cal</sub> = Δε<sub>1</sub> – Δε<sub>2</sub>, representing the total
amplitude of the calculated circular dichroism (CD) couplets) shows
∼10-fold increase in CD amplitude compared to the values observed
for <b>1·</b>DPEA<sub>(<i>R</i>,<i>R</i>)</sub> (<i>A</i><sub>cal</sub>, +187 cm<sup>–1</sup> M<sup>–1</sup>), while <b>1·</b>CHDApy<sub>(<i>S</i>,<i>S</i>)</sub> (<i>A</i><sub>cal</sub>, +1886 cm<sup>–1</sup> M<sup>–1</sup>) shows nearly
3-fold increase of the CD amplitude compared to the value observed
for <b>1·</b>CHDA<sub>(<i>S</i>,<i>S</i>)</sub> (<i>A</i><sub>cal</sub>, −785 cm<sup>–1</sup> M<sup>–1</sup>) at 295 K. The <i>A</i><sub>cal</sub> values of −1759 cm<sup>–1</sup> M<sup>–1</sup> and +1886 cm<sup>–1</sup> M<sup>–1</sup> observed
for the <b>1·</b>DPEApy<sub>(<i>R</i>,<i>R</i>)</sub> and <b>1·</b>CHDApy<sub>(<i>S</i>,<i>S</i>)</sub>, respectively, are extremely high. To
the best of our knowledge, these are some of the largest values reported
for a chirality induction process involving bisporphyrin <i>tweezer</i> receptors. The large enhancement in the CD signal intensity is due
to the well complementarity size between Zn(II)bisporphyrin host and
the extended chiral diamines guest, which results large unidirectional
twisting of two porphyrin units to accommodate the guests having preorganized
binding sites with minimum host–guest steric interactions.
It is interesting to note that <b>1·</b>DPEA<sub>(<i>R</i>,<i>R</i>)</sub> and <b>1·</b>DPEApy<sub>(<i>R</i>,<i>R</i>)</sub> show CD signal opposite
in sign to each other, which happens to be the case between <b>1·</b>CHDA<sub>(<i>S</i>,<i>S</i>)</sub> and <b>1·</b>CHDApy<sub>(<i>S</i>,<i>S</i>)</sub> also
A Nonempirical Approach for Direct Determination of the Absolute Configuration of 1,2-Diols and Amino Alcohols Using Mg(II)bisporphyrin
We
report here a simple, facile, and direct nonempirical protocol
for determining the absolute stereochemistry of a variety of chiral
1,2-diols and amino alcohols at room temperature with no chemical
derivatization using Mg(II)bisporphyrin as a host. Addition of excess
substrates resulted in the formation of a 1:2 host–guest complex
in which two substrates bind in an unusual <i>endo-endo</i> fashion because of interligand H-bonding within the bisporphyrin
cavity leading to the formation of a unidirectional screw in the bisporphyrin
moiety that allowed us an accurate absolute stereochemical determination
of the chiral substrate via exciton-coupled circular dichroism (ECCD).
The sign of the CD couplet has also been found to be inverted when
the stereogenic center is moved by one C atom simply from the bound
to an unbound functionality and thus able to discriminate between
them successfully. Strong complexation of the alcoholic oxygen with
Mg(II)bisporphyrin rigidifies the host–guest complex, which
eventually enhances its ability to stereochemically differentiate
the asymmetric center. The ECCD sign of a large number of substrates
has followed consistent and predictable trends; thus, the system is
widely applicable. Moreover, computational calculations clearly support
the experimental observations along with the absolute stereochemistry
of the chiral substrate