12 research outputs found
Anion-Directed Formation and Degradation of an Interlocked Metallohelicate
Although there are many examples of catenanes, those
of more complex
mechanically interlocked molecular architectures are rare. Additionally,
little attention has been paid to the degradation of such interlocked
systems into their starting complexes, although formation and degradation
are complementary phenomena and are equally important. Interlocked
metallohelicate, [(Pd<sub>2</sub>L<sub>4</sub>)<sub>2</sub>]<sup>8+</sup> (<b>2</b><sup>8+</sup>), is a quadruply interlocked molecular
architecture consisting of two mechanically interlocked monomers,
[Pd<sub>2</sub>L<sub>4</sub>]<sup>4+</sup> (<b>1</b><sup>4+</sup>). <b>2</b><sup>8+</sup> has three internal cavities, each
of which encapsulates one NO<sub>3</sub><sup>–</sup> ion (1:3
host–guest complex, <b>2</b>⊃(NO<sub>3</sub>|NO<sub>3</sub>|NO<sub>3</sub>)<sup>5+</sup>) and is characterized by unusual
thermodynamic stability. However, both the driving force for the dimerization
and the origin of the thermodynamic stability remain unclear. To clarify
these issues, BF<sub>4</sub><sup>–</sup>, PF<sub>6</sub><sup>–</sup>, and OTf<sup>–</sup> have been used to demonstrate
that the dimerization is driven by the anion template effect. Interestingly,
the stability of <b>2</b><sup>8+</sup> strongly depends on the
encapsulated anions (<b>2</b>⊃(NO<sub>3</sub>|NO<sub>3</sub>|NO<sub>3</sub>)<sup>5+</sup> ≫ <b>2</b>⊃(BF<sub>4</sub>|BF<sub>4</sub>|BF<sub>4</sub>)<sup>5+</sup>). The origins
of this differing thermodynamic stability have been shown through
detailed investigations to be due to the differences in the stabilization
of the interlocked structure by the host–guest interaction
and the size of the anion. We have found that 2-naphthalenesulfonate
(ONs<sup>–</sup>) induces the monomerization of <b>2</b>⊃(NO<sub>3</sub>|NO<sub>3</sub>|NO<sub>3</sub>)<sup>5+</sup> via intermediate <b>2</b>⊃(ONs|NO<sub>3</sub>|ONs)<sup>5+</sup>, which is formed by anion exchange. On the basis of this
finding, and using <i>p</i>-toluenesulfonate (OTs<sup>–</sup>), the physical separation of <b>2</b>⊃(NO<sub>3</sub>|NO<sub>3</sub>|NO<sub>3</sub>)<sup>5+</sup> and <b>1</b><sup>4+</sup> as OTs<sup>–</sup> salt was accomplished
Homochiral 1D Helical Chain Based on an Achiral Cu(II) Complex
Self-assembly of an achiral [CuÂ(L)] complex produced
a homochiral
helical chain [CuÂ(L)]<sub>3</sub>·2H<sub>2</sub>O (<b>1</b>) (L = 2-dimethylaminoethylÂ(oxamato)). Interestingly, complex <b>1</b> obtained in our laboratory exhibits only a left-handed helical
chain without any chiral source. Single-crystal X-ray analysis revealed
the absolute structure and homochirality of its helical chain structure
in the space group of <i>P</i>3<sub>2</sub>. Solid-state
circular dichroism (CD) spectra confirmed the high enantio excess
of the crystals obtained in different synthesis batches. Magnetic
susceptibility measurements reveal a relatively strong intrachain
antiferromagnetic interaction between CuÂ(II) centers via an oxamato
bridge (<i>J</i> = −74.4 cm<sup>–1</sup>)
Homochiral 1D Helical Chain Based on an Achiral Cu(II) Complex
Self-assembly of an achiral [CuÂ(L)] complex produced
a homochiral
helical chain [CuÂ(L)]<sub>3</sub>·2H<sub>2</sub>O (<b>1</b>) (L = 2-dimethylaminoethylÂ(oxamato)). Interestingly, complex <b>1</b> obtained in our laboratory exhibits only a left-handed helical
chain without any chiral source. Single-crystal X-ray analysis revealed
the absolute structure and homochirality of its helical chain structure
in the space group of <i>P</i>3<sub>2</sub>. Solid-state
circular dichroism (CD) spectra confirmed the high enantio excess
of the crystals obtained in different synthesis batches. Magnetic
susceptibility measurements reveal a relatively strong intrachain
antiferromagnetic interaction between CuÂ(II) centers via an oxamato
bridge (<i>J</i> = −74.4 cm<sup>–1</sup>)
Stereospecific Synthesis of Tris-heteroleptic Tris-cyclometalated Iridium(III) Complexes via Different Heteroleptic Halogen-Bridged Iridium(III) Dimers and Their Photophysical Properties
Herein,
we report on the stereospecific synthesis of two single
isomers of tris-heteroleptic tris-cyclometalated iridiumÂ(III) (IrÂ(III))
complexes composed of three different nonsymmetric cyclometalating
ligands via heteroleptic halogen-bridged Ir dimers [IrÂ(tpy)Â(F<sub>2</sub>ppy)Â(μ-Br)]<sub>2</sub> <b>17b</b> and [IrÂ(mpiq)Â(F<sub>2</sub>ppy)Â(μ-Br)]<sub>2</sub> <b>27b</b> (tpyH:
(2-(4′-tolyl)ÂpyriÂdine) and F<sub>2</sub>ppyH: (2-(4′,6′-diÂfluoroÂphenyl)Âpyridine),
and mpiqH: (1-(4′-methylÂphenyl)ÂisoÂquinoline))
prepared by Zn<sup>2+</sup>-promoted degradation of IrÂ(tpy)<sub>2</sub>Â(F<sub>2</sub>ppy) <b>21</b> and IrÂ(mpiq)<sub>2</sub>Â(F<sub>2</sub>ppy) <b>26</b>, as reported by us.
Subsequently, <b>17b</b> and <b>27b</b> were converted
to the tris-heteroleptic tris-cyclometalated Ir complexes IrÂ(tpy)Â(F<sub>2</sub>ppy)Â(mpiq) <b>25</b> consisting of tpy, F<sub>2</sub>ppy, and mpiq, as confirmed by spectroscopic data and X-ray
crystal structure analysis. The first important point in this work
is the selective synthesis of specific isomers among eight possible
stereoisomers of Ir complexes having the same combination of three
cyclometalating ligands. Namely, two meridional forms of <b>25</b> were synthesized and isolated. The second finding is that the different
stereoisomers of <b>25</b> have different stability. Finally,
different stereoisomers exhibit different emission spectra. Namely,
one of its stereoisomers <b>25a</b> exhibits a single broad
emission from <i>ca</i>. 550 nm to <i>ca</i>.
650 nm (orange emission), while stereoisomer <b>25c</b> emits
dual emission at <i>ca</i>. 509 nm and <i>ca</i>. 600 nm (pale pink emission), as supported by time-dependent density
functional theory calculation. To the best of our knowledge, this
is the first report of the selective and efficient synthesis of different
stereoisomers of tris-heteroleptic tris-cyclometalated IrÂ(III) complexes
that have different stabilities and different photophysical properties
Facile Synthetic Route to Highly Luminescent Sila[7]helicene
A facile synthetic route to dimethylsila[7]helicene by using a Lewis acid catalyzed double-cyclization reaction for construction of the twisted two phenanthrene moieties is described. Sila[7]helicene exhibited a high fluorescence quantum yield and a realatively large <i>g</i> value (dissymmetric factor) of circularly polarized luminencence (CPL) for small molecules
Facile Synthetic Route to Highly Luminescent Sila[7]helicene
A facile synthetic route to dimethylsila[7]helicene by using a Lewis acid catalyzed double-cyclization reaction for construction of the twisted two phenanthrene moieties is described. Sila[7]helicene exhibited a high fluorescence quantum yield and a realatively large <i>g</i> value (dissymmetric factor) of circularly polarized luminencence (CPL) for small molecules
Efficient Synthesis of Tris-Heteroleptic Iridium(III) Complexes Based on the Zn<sup>2+</sup>-Promoted Degradation of Tris-Cyclometalated Iridium(III) Complexes and Their Photophysical Properties
We
report on the efficient synthesis of tris-heteroleptic iridium
(Ir) complexes based on the degradation of tris-cyclometalated Ir
complexes (IrL<sub>3</sub>, L: cyclometalating ligand) in the presence
of Brønsted and Lewis acids such as HCl (in 1,4-dioxane), AlCl<sub>3</sub>, TMSCl, and ZnX<sub>2</sub> (X = Br or Cl), which affords
the corresponding halogen-bridged Ir dimers (μ-complexes). Tris-cyclometalated
Ir complexes containing electron-withdrawing groups such as fluorine,
nitro, or CF<sub>3</sub> moieties on the ligands were less reactive.
This different reactivity was applied to the selective degradation
of heteroleptic Ir complexes such as <i>fac</i>-IrÂ(tpy)<sub>2</sub>(F<sub>2</sub>ppy) (<i><b>fac</b></i><b>-12</b>) (tpy: 2-(4′-tolyl)Âpyridine and F<sub>2</sub>ppy:
2-(4′,6′-difluorophenyl)Âpyridine), <i>mer</i>-IrÂ(tpy)<sub>2</sub>(F<sub>2</sub>ppy) (<i><b>mer</b></i><b>-12</b>), and <i>mer</i>-IrÂ(mpiq)<sub>2</sub>(F<sub>2</sub>ppy) (<i><b>mer</b></i><b>-15</b>) (mpiq:
1-(4′-methylphenyl)Âisoquinoline). For example, the reaction
of <i><b>mer</b></i><b>-12</b> with ZnBr<sub>2</sub> gave the heteroleptic μ-complex [{IrÂ(tpy)Â(F<sub>2</sub>ppy)Â(μ-Br)}<sub>2</sub>] <b>27b</b> as a major product,
resulting from the selective elimination of the tpy ligand of <i><b>mer</b></i><b>-12</b>, and treatment of <b>27b</b> with acetylacetone (acacH) afforded the corresponding
tris-heteroleptic Ir complex IrÂ(tpy)Â(F<sub>2</sub>ppy)Â(acac)<b>18</b>. In addition, another tris-heteroleptic Ir complex <b>35a</b> having 8-benzeneÂsulfonylÂamidoÂquinoline
(8BSQ) ligand was synthesized. Mechanistic studies of this degradation
reaction and the photochemical properties, especially a dual emission,
of these newly synthesized tris-heteroleptic Ir complexes are also
reported
Synthesis, Characterization, X‑ray Crystal Structure, DFT Calculations, and Catalytic Properties of a Dioxidovanadium(V) Complex Derived from Oxamohydrazide and Pyridoxal: A Model Complex of Vanadate-Dependent Bromoperoxidase
A vanadiumÂ(V) complex with the formula
[Et<sub>3</sub>NH]Â[V<sup>V</sup>O<sub>2</sub>(sox-pydx)] with a new
tridentate ligand 2-[2-[[3-hydroxy-5-(hydroxymethyl)-2-methylpyridin-4-yl]Âmethylene]Âhydrazinyl]-2-oxoacetamide
(soxH-pydxH), obtained by condensation of oxamohydrazide and pyridoxal
(one of the forms of vitamin B<sub>6</sub>), has been synthesized.
The compound was characterized by various analytical and spectroscopic
methods, and its structure was determined by single-crystal X-ray
diffraction technique. Density functional theory (DFT) and time-dependent
DFT calculations were used to understand the electronic structure
of the complex and nature of the electronic transitions observed in
UV–vis spectra. In the complex, vanadiumÂ(V) is found to be
pentacoordinated with two oxido ligands and a bianionic tridentate
ONO-donor ligand. The vanadium center has square-pyramidal geometry
with an axial oxido ligand, and the equatorial positions are occupied
by another oxido ligand and a phenolato oxygen, an imine nitrogen,
and a deprotonated amide oxygen of the hydrazone ligand. A DFT-optimized
structure of the complex shows very similar metrical parameters as
determined by X-ray crystallography. The O<sub>4</sub>N coordination
environment of vanadium and the hydrogen-bonding abilities of the
pendant amide moiety have a strong resemblance with the vanadium center
in bromoperoxidase enzyme. Bromination experiments using H<sub>2</sub>O<sub>2</sub> as the oxidizing agent, with model substrate phenol
red, and the vanadium complex as a catalyst show a remarkably high
value of <i>k</i><sub>cat</sub> equal to 26340 h<sup>–1</sup>. The vanadium compound also efficiently catalyzes bromination of
phenol and salicylaldehyde as well as oxidation of benzene to phenol
by H<sub>2</sub>O<sub>2</sub>
Novel Means of Controlling the Solid-State Circular Dichroism Property in a Supramolecular Organic Fluorophore Comprising 4-[2-(Methylphenyl)ethynyl]benzoic Acid by Varying the Position of the Methyl Substituent
The solid-state circular dichroism (CD) of a 4-[2-(methylphenyl)Âethynyl]Âbenzoic
acid/amine supramolecular organic fluorophore can be controlled by
changing the position of the methyl substituent of the methylphenylethynyl
unit on the achiral 4-[2-(methylphenyl)Âethynyl]Âbenzoic acid component
molecule, instead of changing the chirality of the chiral amine component
molecule
Odds ratio with 95% confidence interval of diabetes according to overtime work hours stratified by participant characteristics.
<p>Abbreviations: BMI, body mass index; Ref, reference.</p><p>*<i>P</i> for trend obtained from multiple logistic regression analysis by assigning 23, 62, 90, and 100 to categories of overtime work.</p>†<p>Adjusted for age (continuous), sex, company, smoking status (never, past, or current), and BMI (kg/m<sup>2</sup>, continuous) in 4 companies (n = 41,081).</p>‡<p>48 women in 1 company were excluded in this analysis due to no diabetic patients.</p>§<p>Adjusted for age (continuous), sex, company, smoking status (never, past, or current), BMI (kg/m<sup>2</sup>, continuous), alcohol use (non-drinker, drinker consuming >0 to <23 g, 23 to <46 g, or ≥46 g of ethanol per day), sleep duration (<6 hours, 6 to <7 hours, or ≥7 hours per day), physical activity (<150 min or ≥150 min per week), family history of diabetes (yes or no), shift work (yes or no), department (field work or non-field work), and job position (high or low) in 1 company (n = 33,807).</p