26 research outputs found
The synthesis, structure, and ethylene polymerization of dimeric salicylaldiminato titanium complexes
Probing Site Cooperativity of Frustrated Phosphine/Borane Lewis Pairs by a Polymerization Study
The first highly
active phosphine (P)/borane (B) Lewis pair polymerization
is promoted unexpectedly by PâB adducts. The P and B site cooperativity
is essential for achieving effective polymerization, as shown by this
study examining the reactivity of a library of P/B Lewis pairs toward
polymerization of a renewable acrylic monomer
A series of new hybrid compounds constructed from Dawson-type phosphomolybdates and metalâorganic coordination complexes
Highly Active Half-Metallocene Yttrium Catalysts for Living and Chemoselective Polymerization of Allyl Methacrylate
Highly active half-metallocene amidinate
yttrium catalysts for
chemoselective and living polymerization of allyl methacrylate are
reported. The living characteristics of allyl methacrylate polymerization
have been proved by three sets of experiments. The generated polymers
exhibit good solubility in DMF, well-controlled molecular weights,
and narrow molecular weight distributions (<i><i>Ä</i></i> < 1.10). The kinetic studies revealed that the catalyst
systems follow a living monometallic coordinationâaddition
polymerization mechanism. The present study is first example for rare
earth metal-catalyzed living coordinationâaddition polymerization
of polar divinyl monomers
Intrinsic interfacial dynamic engineering of zincophilic microbrushes via regulating Zn deposition for highly reversible aqueous zinc ion battery
Aqueous rechargeable zinc ion batteries are promising efficient energy storage systems due to remarkable safety and satisfactory capacity. However, zinc metal anode instability including dendrite growth and side reactions severely hinders widespread applications. Herein, zincophilic microbrushes have been in situ anchored on zinc plates through simple freeze-drying and mild reduction of graphene oxide, successfully overcoming these thorny issues. By introducing suitable oxygen-containing groups, the microbrushes exhibit a good affinity for zinc ions, thereby providing sufficient depositing sites, promoting zinc plating and stripping during cycling, and suppressing side reactions. The delicate zincophilic microbrushes can not only function as protective layer to guide the deposition of zinc ions, but also act as high-speed pathways to redistribute the zinc ion flux for rapid kinetics. Consequently, the microbrushes-covered zinc anode displays long lifespan and good durability, whenever in symmetric cell or full battery tests. This work paves a feasible bridge to design advanced aqueous anodes by architecting both structures and compositions of metal coverings.Ministry of Education (MOE)This work is financially supported by the National Natural Science Foundation of China (21905133, 52174284, 52172204, and 51872139) and MOE AcRF Tier 1 grant no. 2020-T1-001-031 (Singapore)
Spontaneous Resolution of EvansâShowell-Type Polyoxometalates in Constructing Chiral InorganicâOrganic Hybrid Architectures
Six new hybrid compounds based on
[Co<sub>2</sub>Mo<sub>10</sub>H<sub>4</sub>O<sub>38</sub>]<sup>6â</sup> polyoxoanion, (4-H<sub>2</sub>pya)<sub>6</sub>Co<sub>2</sub>Mo<sub>10</sub>H<sub>4</sub>O<sub>38</sub>·10H<sub>2</sub>O <b>1</b> (4-Hpya =3-(4-pyridyl)Âacrylic acid) and (4-H<sub>2</sub>pya)<sub>4</sub>[MÂ(H<sub>2</sub>O)<sub>6</sub>]Â[Co<sub>2</sub>Mo<sub>10</sub>H<sub>4</sub>O<sub>38</sub>]·5H<sub>2</sub>O (M = Co <b>2</b>, Ni <b>3</b>, Cu <b>4</b>, Zn <b>5</b>, Cd <b>6</b>), were synthesized and characterized by elemental analysis,
IR spectroscopy, TG analysis, solid diffuse reflective spectrum, powder
X-ray diffraction, and single crystal X-ray diffraction. Compound <b>1</b> crystallizes in the centrosymmetric space group <i>P</i>-1, which is built up of protonated 4-H<sub>2</sub>pya
molecules and isolated [Co<sub>2</sub>Mo<sub>10</sub>H<sub>4</sub>O<sub>38</sub>]<sup>6â</sup> polyoxoanions. Isostructural
compounds <b>2</b>â<b>6</b> crystallize in the
chiral space group <i>P</i>1 by spontaneous resolution,
as a conglomerate of two enantiomerically pure crystals, which were
obtained by adding different metal cations to the reaction system
of compound <b>1</b>. The structures of <b>2</b>â<b>6</b> comprise chiral [Co<sub>2</sub>Mo<sub>10</sub>H<sub>4</sub>O<sub>38</sub>]<sup>6â</sup> anions, cationic [MÂ(H<sub>2</sub>O)<sub>6</sub>]<sup>2+</sup> units, and protonated 4-H<sub>2</sub>pya ligands. The chiral [Co<sub>2</sub>Mo<sub>10</sub>H<sub>4</sub>O<sub>38</sub>]<sup>6â</sup> polyoxoanions can be connected
up together by directional hydrogen-bonding interactions among terminal
oxygen atoms of anions, coordinated water molecules and organic ligands
to construct a 3D supramolecular chiral framework in <b>2</b>â<b>6</b>. The absolute configuration of <b>2</b>â<b>6</b> was determined from the Flack parameter by
X-ray crystallography and solid state circular dichroism spectroscopy.
As far as we know, compounds <b>2</b>â<b>6</b> represent
the first examples of chiral inroganic-organic hybrid species based
on EvansâShowell-type polyoxometalates. Furthermore, the second
harmonic generation (SHG) activities for <b>2</b> and <b>4</b> were measured, showing an SHG efficiency of approximately
0.9 Ă KH<sub>2</sub>PO<sub>4</sub>
Remarkable Stereochemistry Control in the Polymerization of 뱉Olefins Using a Simple Scandium Catalyst System
A convenient approach to highly isotactic
polyÂ(α-olefin)Âs
(<i>mmmm</i> > 99%) was realized using a simple scandium-based
catalyst system consisting of ScCl<sub>3</sub>(THF)<sub>3</sub>, Al<sup><i>i</i></sup>Bu<sub>3</sub>, and [Ph<sub>3</sub>C]Â[BÂ(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] under mild conditions. The resultant
polymers possess ultrahigh molecular weight (<i>M</i><sub>n</sub> > 10<sup>6</sup>) and relatively narrow molecular weight
distribution. Especially, the excellent stereoselectivity still remains
even at an elevated reaction temperature of 80 °C. Aluminum alkyls
and organic borates, as well as their loadings significantly affected
both the catalyst activity and product stereochemistry. The initial
mechanistic exploration was carried out by means of NMR and ICPâAES
spectroscopy, suggesting that a kind of incompact ion pair might be
the active species. Further efforts to elucidate the real active sites
and stereochemistry control mechanism of the catalytic system are
underway
Spontaneous Resolution of EvansâShowell-Type Polyoxometalates in Constructing Chiral InorganicâOrganic Hybrid Architectures
Six new hybrid compounds based on
[Co<sub>2</sub>Mo<sub>10</sub>H<sub>4</sub>O<sub>38</sub>]<sup>6â</sup> polyoxoanion, (4-H<sub>2</sub>pya)<sub>6</sub>Co<sub>2</sub>Mo<sub>10</sub>H<sub>4</sub>O<sub>38</sub>·10H<sub>2</sub>O <b>1</b> (4-Hpya =3-(4-pyridyl)Âacrylic acid) and (4-H<sub>2</sub>pya)<sub>4</sub>[MÂ(H<sub>2</sub>O)<sub>6</sub>]Â[Co<sub>2</sub>Mo<sub>10</sub>H<sub>4</sub>O<sub>38</sub>]·5H<sub>2</sub>O (M = Co <b>2</b>, Ni <b>3</b>, Cu <b>4</b>, Zn <b>5</b>, Cd <b>6</b>), were synthesized and characterized by elemental analysis,
IR spectroscopy, TG analysis, solid diffuse reflective spectrum, powder
X-ray diffraction, and single crystal X-ray diffraction. Compound <b>1</b> crystallizes in the centrosymmetric space group <i>P</i>-1, which is built up of protonated 4-H<sub>2</sub>pya
molecules and isolated [Co<sub>2</sub>Mo<sub>10</sub>H<sub>4</sub>O<sub>38</sub>]<sup>6â</sup> polyoxoanions. Isostructural
compounds <b>2</b>â<b>6</b> crystallize in the
chiral space group <i>P</i>1 by spontaneous resolution,
as a conglomerate of two enantiomerically pure crystals, which were
obtained by adding different metal cations to the reaction system
of compound <b>1</b>. The structures of <b>2</b>â<b>6</b> comprise chiral [Co<sub>2</sub>Mo<sub>10</sub>H<sub>4</sub>O<sub>38</sub>]<sup>6â</sup> anions, cationic [MÂ(H<sub>2</sub>O)<sub>6</sub>]<sup>2+</sup> units, and protonated 4-H<sub>2</sub>pya ligands. The chiral [Co<sub>2</sub>Mo<sub>10</sub>H<sub>4</sub>O<sub>38</sub>]<sup>6â</sup> polyoxoanions can be connected
up together by directional hydrogen-bonding interactions among terminal
oxygen atoms of anions, coordinated water molecules and organic ligands
to construct a 3D supramolecular chiral framework in <b>2</b>â<b>6</b>. The absolute configuration of <b>2</b>â<b>6</b> was determined from the Flack parameter by
X-ray crystallography and solid state circular dichroism spectroscopy.
As far as we know, compounds <b>2</b>â<b>6</b> represent
the first examples of chiral inroganic-organic hybrid species based
on EvansâShowell-type polyoxometalates. Furthermore, the second
harmonic generation (SHG) activities for <b>2</b> and <b>4</b> were measured, showing an SHG efficiency of approximately
0.9 Ă KH<sub>2</sub>PO<sub>4</sub>
Bis(oxazolinyl)phenyl-Ligated Rare-Earth-Metal Complexes: Highly Regioselective Catalysts for <i>cis</i>-1,4-Polymerization of Isoprene
NCN-pincer (<i>S,S</i>)-2,6-bisÂ(4âČ-isopropyl-2âČ-oxazolinyl)Âphenyl-ligated
rare-earth-metal dichlorides [(<i>S,S</i>)-Phebox-<sup><i>i</i></sup>Pr]ÂLnCl<sub>2</sub>(THF)<sub>2</sub> (Ln = Sc (<b>1</b>); Y (<b>2</b>); Dy (<b>3</b>); Ho (<b>4</b>); Tm (<b>5</b>); Lu (<b>6</b>)) were synthesized via
transmetalation between [(<i>S,S</i>)-Phebox-<sup><i>i</i></sup>Pr]Li and LnCl<sub>3</sub> in THF solvent. Interestingly,
treatment of LaCl<sub>3</sub> by the same method generated trisÂ(ligand)
lanthanum complex [(<i>S,S</i>)-Phebox-<sup><i>i</i></sup>Pr]<sub>3</sub>La (<b>7</b>). Molecular structures of
complexes <b>1</b>, <b>2</b>, <b>3</b>, and <b>7</b> were established by single-crystal X-ray diffraction study.
Pincer ligand (<i>S,S</i>)-Phebox-<sup><i>i</i></sup>Pr adopts a ÎșC:ÎșN:ÎșNâČ tridentate coordination
mode to the central metal ion. Upon activation with [PhNHMe<sub>2</sub>]Â[BÂ(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] and Al<sup><i>i</i></sup>Bu<sub>3</sub>, complexes <b>2</b>â<b>5</b> exhibited highly catalytic activities and more than 98% <i>cis</i>-1,4-selectivity for isoprene polymerization while complexes <b>1</b> and <b>6</b> were inactive for this reaction. When
use of the catalyst system consisted of complex <b>2</b>, [PhNHMe<sub>2</sub>]Â[BÂ(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>], and Al<sup><i>i</i></sup>Bu<sub>3</sub> for isoprene polymerization, the resultant
polymer has a high <i>cis</i>-1,4-selectivity up to 99.5%.
The reaction temperature had little effect on the regioselectivity,
and high <i>cis</i>-1,4-selectivity almost remained even
at 80 °C
Remarkable Stereochemistry Control in the Polymerization of 뱉Olefins Using a Simple Scandium Catalyst System
A convenient approach to highly isotactic
polyÂ(α-olefin)Âs
(<i>mmmm</i> > 99%) was realized using a simple scandium-based
catalyst system consisting of ScCl<sub>3</sub>(THF)<sub>3</sub>, Al<sup><i>i</i></sup>Bu<sub>3</sub>, and [Ph<sub>3</sub>C]Â[BÂ(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] under mild conditions. The resultant
polymers possess ultrahigh molecular weight (<i>M</i><sub>n</sub> > 10<sup>6</sup>) and relatively narrow molecular weight
distribution. Especially, the excellent stereoselectivity still remains
even at an elevated reaction temperature of 80 °C. Aluminum alkyls
and organic borates, as well as their loadings significantly affected
both the catalyst activity and product stereochemistry. The initial
mechanistic exploration was carried out by means of NMR and ICPâAES
spectroscopy, suggesting that a kind of incompact ion pair might be
the active species. Further efforts to elucidate the real active sites
and stereochemistry control mechanism of the catalytic system are
underway