34 research outputs found
Cu(II)-Mediated Sulfonylation of (Hetero)arenes with TosMIC Using Monodentate Directing Groups
Monodentate chelation-assisted direct ortho-C–H
sulfonylation of (hetero)arenes using TosMIC as the novel sulfonylating
reagent has been developed. A broad range of substrates, including
indolines, indoles, 2-phenylpyridines, and others were well tolerated
to afford the corresponding products in moderate to good yields. Mechanistic
studies revealed that the sulfonyl radical might be involved. Inspired
by the above discovery, preliminary para-C–H
sulfonylation of naphthalene substrate was also successfully realized.
The current protocol featured with cheap metal catalysis, good functional
group compatibility, and operational convenience
Chiral CNN Pincer Palladium(II) Complexes with 2‑Aryl-6-(oxazolinyl)pyridine Ligands: Synthesis, Characterization, and Application to Enantioselective Allylation of Isatins and Suzuki–Miyaura Coupling Reaction
A series
of chiral 2-aryl-6-(oxazolinyl)Âpyridine (aryl = phenyl
or 1-naphthyl) ligands <b>2a</b>–<b>f</b> were
conveniently prepared from commercially available 6-bromo-2-picolinaldehyde
in two steps. Reaction of <b>2a</b>–<b>f</b> with
PdCl<sub>2</sub> in toluene in the presence of sodium bicarbonate
afforded the corresponding CNN pincer PdÂ(II) complexes <b>3a</b>–<b>f</b> via aryl C–H bond activation of the
related ligands. All of the new compounds have been fully characterized
by elemental analysis (MS for ligands), <sup>1</sup>H and <sup>13</sup>C NMR, and IR spectra. In addition, the molecular structures of PdÂ(II)
complexes <b>3c</b>–<b>f</b> have been determined
by X-ray single-crystal diffraction. The obtained chiral pincer catalysts
were successfully used in the asymmetric allylation of isatins with
allyltributyltin, giving the corresponding 3-allyl-3-hydroxyoxindoles
in high yields with enantioselectivities of up to 86% ee. These pincers
could also catalyze the asymmetric Suzuki–Miyaura coupling
reaction to provide the axially chiral biaryl products in good yields
with good stereoselectivities (up to 68% ee)
PCN Pincer Palladium(II) Complex Catalyzed Enantioselective Hydrophosphination of Enones: Synthesis of Pyridine-Functionalized Chiral Phosphine Oxides as NC<sub>sp<sup>3</sup></sub>O Pincer Preligands
A series
of chiral PCN pincer PdÂ(II) complexes <b>VI</b>–<b>XIII</b> with aryl-based aminophosphine–imidazoline or
phosphinite–imidazoline ligands were synthesized and characterized.
They were examined as enantioselective catalysts for the hydrophosphination
of enones. Among them, complex <b>IX</b>, which features a Ph<sub>2</sub>PO donor as well as an imidazoline donor with (4<i>S</i>)-phenyl and <i>N</i>-Tol-<i>p</i> groups, was
found to be the optimal catalyst. Thus, in the presence of 2–5
mol % of complex <b>IX</b> a wide variety of enones reacted
smoothly with diarylphosphines to give the corresponding chiral phosphine
derivatives in high yields with enantioselectivities of up to 98%
ee. In particular, heteroaryl species such as 2-thienyl-, 2-furyl-,
and 2-pyridinyl-containing enones that have a strong coordination
ability to the Pd center were also appropriate substrates for the
current catalytic system. For example, hydrophosphination of 2-alkenoylpyridines
with diphenylphosphine followed by oxidation with H<sub>2</sub>O<sub>2</sub> afforded the corresponding pyridine-functionalized chiral
phosphine oxides in good yields with good to excellent enantioselectivities
(10 examples, up to 95% ee). Furthermore, it had been demonstrated
that the obtained pyridine-containing phosphine oxide acted as a tridentate
ligand in the reaction with PdCl<sub>2</sub> to form an intriguing
NC<sub>sp<sup>3</sup></sub>O pincer PdÂ(II) complex via C<sub>sp<sup>3</sup></sub>–H bond activation, which to our knowledge is
the first example of a chiral DC<sub>sp<sup>3</sup></sub>D′
Pd pincer (D ≠D′; D and D′ denote donor atoms
such as P, N, etc.)
Chiral CNN Pincer Palladium(II) Complexes with 2‑Aryl-6-(oxazolinyl)pyridine Ligands: Synthesis, Characterization, and Application to Enantioselective Allylation of Isatins and Suzuki–Miyaura Coupling Reaction
A series
of chiral 2-aryl-6-(oxazolinyl)Âpyridine (aryl = phenyl
or 1-naphthyl) ligands <b>2a</b>–<b>f</b> were
conveniently prepared from commercially available 6-bromo-2-picolinaldehyde
in two steps. Reaction of <b>2a</b>–<b>f</b> with
PdCl<sub>2</sub> in toluene in the presence of sodium bicarbonate
afforded the corresponding CNN pincer PdÂ(II) complexes <b>3a</b>–<b>f</b> via aryl C–H bond activation of the
related ligands. All of the new compounds have been fully characterized
by elemental analysis (MS for ligands), <sup>1</sup>H and <sup>13</sup>C NMR, and IR spectra. In addition, the molecular structures of PdÂ(II)
complexes <b>3c</b>–<b>f</b> have been determined
by X-ray single-crystal diffraction. The obtained chiral pincer catalysts
were successfully used in the asymmetric allylation of isatins with
allyltributyltin, giving the corresponding 3-allyl-3-hydroxyoxindoles
in high yields with enantioselectivities of up to 86% ee. These pincers
could also catalyze the asymmetric Suzuki–Miyaura coupling
reaction to provide the axially chiral biaryl products in good yields
with good stereoselectivities (up to 68% ee)
Regioselective 2,2,2-Trifluoroethylation of Imidazopyridines by Visible Light Photoredox Catalysis
A visible-light-induced
C-3 selective trifluoroethylation of imidazoheterocycles
using 1,1,1-trifluoro-2-iodoethane as trifluoroethyl radical sources
was developed. The methodology enables the introduction of a trifluoroethyl
group in a fast and efficient reaction under mild conditions with
excellent regioselectivities and high functional group tolerance
Enantiomeric Separations of Chiral Sulfonic and Phosphoric Acids with Barium-Doped Cyclofructan Selectors via an Ion Interaction Mechanism
New
cyclofructan-6 (CF6)-based chiral stationary phases (CSPs)
bind barium cations. As a result, the barium-complexed CSPs exhibit
enantioselectivity toward 16 chiral phosphoric and sulfonic acids
in the polar organic mode (e.g., methanol or ethanol mobile phase
containing a barium salt additive). Retention is predominantly governed
by a strong ionic interaction between the analyte and the complexed
barium cation as well as hydrogen bonding with the cyclofructan macrocycle.
The log <i>k</i> versus log [X], where [X] = the concentration
of the barium counteranion, plots for LARIHC–CF6-P were linear
with negative slopes demonstrating typical anion exchange behavior.
The nature of the barium counteranion also was investigated (acetate,
methanesulfonate, trifluoroacetate, and perchlorate), and the apparent
elution strength was found to be acetate > methanesulfonate >
trifluoroacetate
> perchlorate. A theory based upon a double layer model was proposed
wherein kosmotropic anions are selectively adsorbed to the cyclofructan
macrocycle and attenuate the effect of the barium cation. van’t
Hoff studies for two analytes were conducted on the LARIHC–CF6-P
for three of the barium salts (acetate, trifluoroacetate, and perchlorate),
and the thermodynamic parameters governing retention and enantioselectivity
are discussed. Interestingly, for the entropically driven separations,
enantiomeric selectivity can increase at higher temperatures, even
with decreasing retention
Chiral Bis(imidazolinyl)phenyl NCN Pincer Rhodium(III) Catalysts for Enantioselective Allylation of Aldehydes and Carbonyl–Ene Reaction of Trifluoropyruvates
Chiral NCN pincer
rhodiumÂ(III) complexes with bisÂ(imidazolinyl)Âphenyl
ligands were found to be effective catalysts for the allylation of
a variety of electronically and structurally diverse aldehydes with
allyltributyltin, giving the corresponding optically active homoallylic
alcohols in high yields with enantioselectivities of up to 97% <i>ee</i>. These complexes were also applied in the carbonyl–ene
reaction of ethyl or methyl trifluoropyruvate with various 2-arylpropenes.
With the aid of silver trifluoromethanesulfonate, the pincer rhodiumÂ(III)
catalysts could catalyze the reaction to provide the corresponding
chiral α-hydroxy-α-trifluoromethyl esters in good yields
with high stereoselectivities (up to 95% <i>ee</i>)
Enantioselective Hydrophosphination of Enones with Diphenylphosphine Catalyzed by Bis(imidazoline) NCN Pincer Palladium(II) Complexes
A series
of chiral NCN pincer PdÂ(II) complexes with 1,3-bisÂ(2′-imidazolinyl)Âphenyl
(Phebim) ligands were synthesized via the C–H activation or
oxidative addition method. A dinuclear macrocyclic PdÂ(II) complex
was also prepared by reaction of the Phebim-H ligand with PdCl<sub>2</sub>. All of the new compounds were fully characterized, and X-ray
single-crystal structures were obtained for two of the complexes.
The PdÂ(II) complexes were successfully applied to enantioselective
hydrophosphination of various enones with diphenylphosphine, providing
optically active phosphine derivatives in good yields with enantioselectivities
of up to 94% ee
Visual Gustation via Regulable Elastic Photonic Crystals
The unique structural sensitivity of photonic crystals
(PCs) endows
them with stretchable or elastic tunability for light propagation
and spontaneous emission modulation. Hydrogel PCs have been demonstrated
to have biocompatibility and flexibility for potential human health
detection and environmental security monitoring. However, current
elastic PCs still possess a fixed elastic modulus and uncontrollable
structural colors based on a tunable elastic modulus, posing considerable
challenges for in situ detection, particularly in wearable or portable
sensing devices. In this work, we introduced a novel chemo-mechanical
transduction mechanism embedded within a photonic crystal nanomatrix,
leading to the creation of structural colors and giving rise to a
visual gustation sensing experience. By utilizing the captivating
structural colors generated by the hydrogel PC, we employ abundant
optical information to identify various analytes. The finite element
analysis proved the electric field distribution in the PC matrix during
stretch operations. The elastic-optical behaviors with various chemical
cosolvents, including cations, anions, saccharides, or organic acids,
were investigated. The mechanism of the Hofmeister effect regulating
the elasticity of hydrogels was demonstrated with the network nanostructure
of the hydrogels. The hydrogel PC matrix demonstrates remarkable
capability in efficiently distinguishing a wide range of cations,
anions, saccharides, and organic acids across various concentrations,
mixtures, and even real food samples, such as tastes and soups. Through
comprehensive research, a precise relationship between the structural
colors and the elastic modulus of hydrogel PCs has been established,
contributing to the biomatching elastic-optics platform for wearable
devices, a dynamic environment, and clinical or health monitoring
auxiliary
New Type of 2,6-Bis(imidazo[1,2‑<i>a</i>]pyridin-2-yl)pyridine-Based Ruthenium Complexes: Active Catalysts for Transfer Hydrogenation of Ketones
Neutral
and cationic rutheniumÂ(II) complexes bearing a symmetrical 2,6-bisÂ(imidazoÂ[1,2-<i>a</i>]Âpyridin-2-yl)Âpyridine were synthesized and structurally
characterized by NMR analysis and X-ray crystallographic determinations.
These complexes have exhibited good catalytic activity in the transfer
hydrogenation of ketones. In refluxing isopropyl alcohol, the conversion
of the substrates reached up to 99%, and a TOF value of 356 400
h<sup>–1</sup> with 0.1 mol % catalyst was achieved