19 research outputs found
Jahn–Teller Distortion in Polyoligomeric Silsesquioxane (POSS) Cations
We investigated the symmetry breaking
mechanism in cubic octa-<i>tert</i>-butyl silsesquioxane
and octachloro silsesquioxane
monocations (Si<sub>8</sub>O<sub>12</sub>(CÂ(CH<sub>3</sub>)<sub>3</sub>)<sub>8</sub><sup>+</sup> and Si<sub>8</sub>O<sub>12</sub>Cl<sub>8</sub><sup>+</sup>) using density functional theory (DFT) and group
theory. Under <i>O</i><sub><i>h</i></sub> symmetry,
these ions possess <sup>2</sup>T<sub>2g</sub> and <sup>2</sup>E<sub>g</sub> electronic states and undergo different symmetry breaking
mechanisms. The ground states of Si<sub>8</sub>O<sub>12</sub>(CÂ(CH<sub>3</sub>)<sub>3</sub>)<sub>8</sub><sup>+</sup> and Si<sub>8</sub>O<sub>12</sub>Cl<sub>8</sub><sup>+</sup> belong to the <i>C</i><sub>3<i>v</i></sub> and <i>D</i><sub>4<i>h</i></sub> point groups and are characterized by Jahn–Teller
stabilization energies of 3959 and 1328 cm<sup>–1</sup>, respectively,
at the B3LYP/def2-SVP level of theory. The symmetry distortion mechanism
in Si<sub>8</sub>O<sub>12</sub>Cl<sub>8</sub><sup>+</sup> is Jahn–Teller
type, whereas in Si<sub>8</sub>O<sub>12</sub>(CÂ(CH<sub>3</sub>)<sub>3</sub>)<sub>8</sub><sup>+</sup> the distortion is a combination
of both Jahn–Teller and pseudo-Jahn–Teller effects.
The distortion force acting in Si<sub>8</sub>O<sub>12</sub>(CÂ(CH<sub>3</sub>)<sub>3</sub>)<sub>8</sub><sup>+</sup> is mainly localized
on one Si–(<i>tert</i>-butyl) group, while in Si<sub>8</sub>O<sub>12</sub>Cl<sub>8</sub><sup>+</sup> it is distributed
over the oxygen atoms. The main distortion forces acting on the Si<sub>8</sub>O<sub>12</sub> core arise from the coupling between the electronic
state and the vibrational modes, identified as 9t<sub>2g</sub> + 1e<sub>g</sub> + 3a<sub>2u</sub> for the Si<sub>8</sub>O<sub>12</sub>(CÂ(CH<sub>3</sub>)<sub>3</sub>)<sub>8</sub><sup>+</sup> and 1e<sub>g</sub> +
2e<sub>g</sub> for Si<sub>8</sub>O<sub>12</sub>Cl<sub>8</sub><sup>+</sup>
One-Point Binding Ligands for Asymmetric Gold Catalysis: Phosphoramidites with a TADDOL-Related but Acyclic Backbone
Readily available phosphoramidites incorporating TADDOL-related
diols with an acyclic backbone turned out to be excellent ligands
for asymmetric gold catalysis, allowing a number of mechanistically
different transformations to be performed with good to outstanding
enantioselectivities. This includes [2 + 2] and [4 + 2] cycloadditions
of ene-allenes, cycloisomerizations of enynes, hydroarylation reactions
with formation of indolines, as well as intramolecular hydroaminations
and hydroalkoxylations of allenes. Their preparative relevance is
underscored by an application to an efficient synthesis of the antidepressive
drug candidate (−)-GSK 1360707. The distinctive design element
of the new ligands is their acyclic dimethyl ether backbone in lieu
of the (isopropylidene) acetal moiety characteristic for traditional
TADDOL’s. Crystallographic data in combination with computational
studies allow the efficiency of the gold complexes endowed with such
one-point binding ligands to be rationalized
Extraction and coordination behavior of diphenyl hydrogen phosphine oxide towards actinides
<p>Extraction behavior of some selected actinides like U(VI), Th(IV), and Am(III) was investigated with three different H-phosphine oxides, <i>viz.</i> diphenyl hydrogen phosphine oxide (DPhPO), dihexyl hydrogen phosphine oxide (DHePO) and diphenyl phosphite (DPP). The H-phosphine oxides exhibited a dual nature towards the extraction of actinides where the ligand not only extracts the metals by cation exchange but also by coordination with the phosphoryl group at lower and higher acidic concentrations, respectively. Among all ligands employed, DPhPO showed highest extraction with actinides with a substituent dependent trend as follows: DPhPOÂ >Â DHePOÂ >Â DPP. This trend emphasizes the importance of substituents around the phosphine oxide towards their extraction of actinides. The coordination behavior of DPhPO was studied by investigating its corresponding complexes with Th(NO<sub>3</sub>)<sub>4</sub> and UO<sub>2</sub>(NO<sub>3</sub>)<sub>2</sub>. The metal complexes of these actinides were characterized using FT-IR, <sup>1</sup>H and <sup>31</sup>P NMR spectroscopic techniques. Density Functional Theory (DFT) calculations were also performed to understand the electronic and geometric structure of the ligand and the corresponding metal complexes.</p
One-Point Binding Ligands for Asymmetric Gold Catalysis: Phosphoramidites with a TADDOL-Related but Acyclic Backbone
Readily available phosphoramidites incorporating TADDOL-related
diols with an acyclic backbone turned out to be excellent ligands
for asymmetric gold catalysis, allowing a number of mechanistically
different transformations to be performed with good to outstanding
enantioselectivities. This includes [2 + 2] and [4 + 2] cycloadditions
of ene-allenes, cycloisomerizations of enynes, hydroarylation reactions
with formation of indolines, as well as intramolecular hydroaminations
and hydroalkoxylations of allenes. Their preparative relevance is
underscored by an application to an efficient synthesis of the antidepressive
drug candidate (−)-GSK 1360707. The distinctive design element
of the new ligands is their acyclic dimethyl ether backbone in lieu
of the (isopropylidene) acetal moiety characteristic for traditional
TADDOL’s. Crystallographic data in combination with computational
studies allow the efficiency of the gold complexes endowed with such
one-point binding ligands to be rationalized
One-Point Binding Ligands for Asymmetric Gold Catalysis: Phosphoramidites with a TADDOL-Related but Acyclic Backbone
Readily available phosphoramidites incorporating TADDOL-related
diols with an acyclic backbone turned out to be excellent ligands
for asymmetric gold catalysis, allowing a number of mechanistically
different transformations to be performed with good to outstanding
enantioselectivities. This includes [2 + 2] and [4 + 2] cycloadditions
of ene-allenes, cycloisomerizations of enynes, hydroarylation reactions
with formation of indolines, as well as intramolecular hydroaminations
and hydroalkoxylations of allenes. Their preparative relevance is
underscored by an application to an efficient synthesis of the antidepressive
drug candidate (−)-GSK 1360707. The distinctive design element
of the new ligands is their acyclic dimethyl ether backbone in lieu
of the (isopropylidene) acetal moiety characteristic for traditional
TADDOL’s. Crystallographic data in combination with computational
studies allow the efficiency of the gold complexes endowed with such
one-point binding ligands to be rationalized
One-Point Binding Ligands for Asymmetric Gold Catalysis: Phosphoramidites with a TADDOL-Related but Acyclic Backbone
Readily available phosphoramidites incorporating TADDOL-related
diols with an acyclic backbone turned out to be excellent ligands
for asymmetric gold catalysis, allowing a number of mechanistically
different transformations to be performed with good to outstanding
enantioselectivities. This includes [2 + 2] and [4 + 2] cycloadditions
of ene-allenes, cycloisomerizations of enynes, hydroarylation reactions
with formation of indolines, as well as intramolecular hydroaminations
and hydroalkoxylations of allenes. Their preparative relevance is
underscored by an application to an efficient synthesis of the antidepressive
drug candidate (−)-GSK 1360707. The distinctive design element
of the new ligands is their acyclic dimethyl ether backbone in lieu
of the (isopropylidene) acetal moiety characteristic for traditional
TADDOL’s. Crystallographic data in combination with computational
studies allow the efficiency of the gold complexes endowed with such
one-point binding ligands to be rationalized
One-Point Binding Ligands for Asymmetric Gold Catalysis: Phosphoramidites with a TADDOL-Related but Acyclic Backbone
Readily available phosphoramidites incorporating TADDOL-related
diols with an acyclic backbone turned out to be excellent ligands
for asymmetric gold catalysis, allowing a number of mechanistically
different transformations to be performed with good to outstanding
enantioselectivities. This includes [2 + 2] and [4 + 2] cycloadditions
of ene-allenes, cycloisomerizations of enynes, hydroarylation reactions
with formation of indolines, as well as intramolecular hydroaminations
and hydroalkoxylations of allenes. Their preparative relevance is
underscored by an application to an efficient synthesis of the antidepressive
drug candidate (−)-GSK 1360707. The distinctive design element
of the new ligands is their acyclic dimethyl ether backbone in lieu
of the (isopropylidene) acetal moiety characteristic for traditional
TADDOL’s. Crystallographic data in combination with computational
studies allow the efficiency of the gold complexes endowed with such
one-point binding ligands to be rationalized
One-Point Binding Ligands for Asymmetric Gold Catalysis: Phosphoramidites with a TADDOL-Related but Acyclic Backbone
Readily available phosphoramidites incorporating TADDOL-related
diols with an acyclic backbone turned out to be excellent ligands
for asymmetric gold catalysis, allowing a number of mechanistically
different transformations to be performed with good to outstanding
enantioselectivities. This includes [2 + 2] and [4 + 2] cycloadditions
of ene-allenes, cycloisomerizations of enynes, hydroarylation reactions
with formation of indolines, as well as intramolecular hydroaminations
and hydroalkoxylations of allenes. Their preparative relevance is
underscored by an application to an efficient synthesis of the antidepressive
drug candidate (−)-GSK 1360707. The distinctive design element
of the new ligands is their acyclic dimethyl ether backbone in lieu
of the (isopropylidene) acetal moiety characteristic for traditional
TADDOL’s. Crystallographic data in combination with computational
studies allow the efficiency of the gold complexes endowed with such
one-point binding ligands to be rationalized
One-Point Binding Ligands for Asymmetric Gold Catalysis: Phosphoramidites with a TADDOL-Related but Acyclic Backbone
Readily available phosphoramidites incorporating TADDOL-related
diols with an acyclic backbone turned out to be excellent ligands
for asymmetric gold catalysis, allowing a number of mechanistically
different transformations to be performed with good to outstanding
enantioselectivities. This includes [2 + 2] and [4 + 2] cycloadditions
of ene-allenes, cycloisomerizations of enynes, hydroarylation reactions
with formation of indolines, as well as intramolecular hydroaminations
and hydroalkoxylations of allenes. Their preparative relevance is
underscored by an application to an efficient synthesis of the antidepressive
drug candidate (−)-GSK 1360707. The distinctive design element
of the new ligands is their acyclic dimethyl ether backbone in lieu
of the (isopropylidene) acetal moiety characteristic for traditional
TADDOL’s. Crystallographic data in combination with computational
studies allow the efficiency of the gold complexes endowed with such
one-point binding ligands to be rationalized
One-Point Binding Ligands for Asymmetric Gold Catalysis: Phosphoramidites with a TADDOL-Related but Acyclic Backbone
Readily available phosphoramidites incorporating TADDOL-related
diols with an acyclic backbone turned out to be excellent ligands
for asymmetric gold catalysis, allowing a number of mechanistically
different transformations to be performed with good to outstanding
enantioselectivities. This includes [2 + 2] and [4 + 2] cycloadditions
of ene-allenes, cycloisomerizations of enynes, hydroarylation reactions
with formation of indolines, as well as intramolecular hydroaminations
and hydroalkoxylations of allenes. Their preparative relevance is
underscored by an application to an efficient synthesis of the antidepressive
drug candidate (−)-GSK 1360707. The distinctive design element
of the new ligands is their acyclic dimethyl ether backbone in lieu
of the (isopropylidene) acetal moiety characteristic for traditional
TADDOL’s. Crystallographic data in combination with computational
studies allow the efficiency of the gold complexes endowed with such
one-point binding ligands to be rationalized