22 research outputs found
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Redox Control of Aluminum Ring-Opening Polymerization: A Combined Experimental and DFT Investigation
The synthesis, characterization,
and reactivity of an aluminum
alkoxide complex supported by a ferrocene-based ligand, (thiolfan*)ÂAlÂ(O<sup><i>t</i></sup>Bu) (<b>1</b><sup><b>red</b></sup>, thiolfan* = 1,1′-diÂ(2,4-di-<i>tert</i>-butyl-6-thiophenoxy)Âferrocene),
are reported. The homopolymers of l-lactide (LA), ε-caprolactone
(CL), δ-valerolactone (VL), cyclohexene oxide (CHO), trimethylene
carbonate (TMC), and their copolymers were obtained in a controlled
manner by using redox reagents. Detailed DFT calculations and experimental
studies were performed to investigate the mechanism. Mechanistic studies
show that, after the insertion of the first monomer, the coordination
effect of the carbonyl group, which has usually been ignored in previous
reports, can significantly change the energy barrier of the propagation
steps, thus playing an important role in polymerization and copolymerization
processes
Mechanistic Studies of Redox-Switchable Copolymerization of Lactide and Cyclohexene Oxide by a Zirconium Complex
Several aspects of
the copolymerization of l-lactide (LA)
and cyclohexene oxide (CHO) by a redox-switchable zirconium catalyst,
(salfan)ÂZrÂ(O<sup><i>t</i></sup>Bu)<sub>2</sub> (salfan =
1,1′-bisÂ(2-<i>tert</i>-butyl-6-<i>N</i>-methylmethylenephenoxy)Âferrocene), were examined, such as the mechanism
of cyclohexene oxide polymerization, the reactivity of [(salfan)ÂZrÂ(O<sup><i>t</i></sup>Bu)<sub>2</sub>]Â[BAr<sup>F</sup>] (BAr<sup>F</sup> = tetrakisÂ(3,5-bisÂ(trifluoromethyl)Âphenyl)Âborate) toward
lactide, and comonomer effects on polymerization rates. Experimental
methods and DFT calculations indicate that the likely mechanism of
CHO polymerization by [(salfan)ÂZrÂ(O<sup><i>t</i></sup>Bu)<sub>2</sub>]Â[BAr<sup>F</sup>] is coordination insertion and not a cationic
pathway, as employed by the majority of cationic catalysts. Furthermore,
DFT calculations showed that the polymerization of LA by [(salfan)ÂZrÂ(O<sup><i>t</i></sup>Bu)<sub>2</sub>]Â[BAr<sup>F</sup>] is not
thermodynamically favored, in agreement with experimental results.
Finally, we found that the conversion times of CHO or LA from block
to block correlate with the amount of monomer left from the previous
block rather than other factors
Redox Control of Aluminum Ring-Opening Polymerization: A Combined Experimental and DFT Investigation
The synthesis, characterization,
and reactivity of an aluminum
alkoxide complex supported by a ferrocene-based ligand, (thiolfan*)ÂAlÂ(O<sup><i>t</i></sup>Bu) (<b>1</b><sup><b>red</b></sup>, thiolfan* = 1,1′-diÂ(2,4-di-<i>tert</i>-butyl-6-thiophenoxy)Âferrocene),
are reported. The homopolymers of l-lactide (LA), ε-caprolactone
(CL), δ-valerolactone (VL), cyclohexene oxide (CHO), trimethylene
carbonate (TMC), and their copolymers were obtained in a controlled
manner by using redox reagents. Detailed DFT calculations and experimental
studies were performed to investigate the mechanism. Mechanistic studies
show that, after the insertion of the first monomer, the coordination
effect of the carbonyl group, which has usually been ignored in previous
reports, can significantly change the energy barrier of the propagation
steps, thus playing an important role in polymerization and copolymerization
processes
Isolable and Well-Defined Butadienyl Organocopper(I) Aggregates: Facile Synthesis, Structural Characterization, and Reaction Chemistry
Four
types of alkenyl organocopperÂ(I) aggregates linked by 1,3-butadienyl
and/or 1,3,5,7-octatetraenyl moieties were selectively realized in
good isolated yields. All these organocopperÂ(I) aggregates were structurally
characterized by single-crystal X-ray structural analysis. These unprecedented
aggregates, stabilized by multiple Cu–Cu interactions and the
conjugated 1,3-butadienyl or 1,3,5,7-octatetraenyl bridges, could
undergo controlled structural transformations. The 1,4-dicopper 1,3-butadienyl
aggregate <b>3</b> could be efficiently transformed to aggregate <b>2</b>, while LiI could disaggregate the 1,3-butadienyl-1,3,5,7-octatetraenyl
aggregate <b>4</b> to 1,3,5,7-octatetraenyl aggregate <b>5</b> and 1,3-butadienyl aggregate <b>2</b>. Preliminary
reaction chemistry and synthetic applications of these organocopperÂ(I)
aggregates were also investigated
Construction of Octaalkyl-Substituted and Decasubstituted <i>all</i>-<i>cis</i>-Octatetraenes via Linear Dimerization of 1,4-Dicopper-1,3-butadienes and Subsequent Cross-Coupling with Halides
Lithium iodide-assisted linear dimerization of 1,4-dicopper-1,3-butadienes and subsequent Pd-catalyzed cross-coupling reaction with halides provide an efficient way to construct octaalkyl-substituted and decasubstituted <i>all</i>-<i>cis</i> octatetraenes
Lithium Aluminate Complexes and Alumoles from 1,4-Dilithio-1,3-Butadienes and AlEt<sub>2</sub>Cl
A series
of lithium aluminate complexes and alumoles were synthesized from
1,4-dilithio-1,3-butadienes <b>1</b> and AlEt<sub>2</sub>Cl.
Their structures were characterized using single-crystal X-ray structural
analysis and NMR spectroscopy. The structure of the lithium aluminate
complex <b>2</b>-TMEDA showed that the Al atom adopted a tetra-coordinated
mode bonded with two butadienyl C<sub>sp2</sub> atoms and two ethyl
C<sub>sp3</sub> atoms. The lithium cation was located above the alumole
ring. The structure of <b>3a</b> revealed a dimeric 1-ethylalumole
in the solid state. Diffusion ordered spectroscopy NMR spectra showed
that <b>3a</b> was also a dimer in C<sub>6</sub>D<sub>6</sub> solvent. However, in tetrahydrofuran (THF) solution, the dimeric <b>3a</b> dissociated into the 1-ethylalumole–THF adduct.
The lithium aluminate complex <b>2</b> transformed into <b>3a</b>-THF when treated with 1.0 equiv of AlEt<sub>2</sub>Cl.
Preliminary reaction chemistry and synthetic applications of the lithium
aluminate complex were also investigated
Isolable and Well-Defined Butadienyl Organocopper(I) Aggregates: Facile Synthesis, Structural Characterization, and Reaction Chemistry
Four
types of alkenyl organocopperÂ(I) aggregates linked by 1,3-butadienyl
and/or 1,3,5,7-octatetraenyl moieties were selectively realized in
good isolated yields. All these organocopperÂ(I) aggregates were structurally
characterized by single-crystal X-ray structural analysis. These unprecedented
aggregates, stabilized by multiple Cu–Cu interactions and the
conjugated 1,3-butadienyl or 1,3,5,7-octatetraenyl bridges, could
undergo controlled structural transformations. The 1,4-dicopper 1,3-butadienyl
aggregate <b>3</b> could be efficiently transformed to aggregate <b>2</b>, while LiI could disaggregate the 1,3-butadienyl-1,3,5,7-octatetraenyl
aggregate <b>4</b> to 1,3,5,7-octatetraenyl aggregate <b>5</b> and 1,3-butadienyl aggregate <b>2</b>. Preliminary
reaction chemistry and synthetic applications of these organocopperÂ(I)
aggregates were also investigated
Construction of Octaalkyl-Substituted and Decasubstituted <i>all</i>-<i>cis</i>-Octatetraenes via Linear Dimerization of 1,4-Dicopper-1,3-butadienes and Subsequent Cross-Coupling with Halides
Lithium iodide-assisted linear dimerization of 1,4-dicopper-1,3-butadienes and subsequent Pd-catalyzed cross-coupling reaction with halides provide an efficient way to construct octaalkyl-substituted and decasubstituted <i>all</i>-<i>cis</i> octatetraenes
<i>N</i>‑Aryloxide-Amidinate Thorium Complexes
An N-aryloxide-amidine ligand (1),
[ONNO] ligand, integrating phenoxide (PhO–) and
amidine ligands through methylene linkers, was employed in actinide
chemistry. Upon reaction of the deprotonated ligand with ThCl4(DME)2 in ether, the corresponding dimer complex 2 was obtained. Upon treatment of 2 with KCp*
(Cp* = Cp(Me)5) in tetrahydrofuran, the corresponding {[ONNO]ThIVCp*(LiCl)}2 (4) was obtained. In
complex 2, the two ArO– arms bonded
from the same ligand to different ThIV centers. In contrast,
both ArO– arms coordinated to the same metal center
in 4. Notably, when a mixture of 2 and bipyridine
was treated with one or two equiv of KC8, the [ONNO]ThIV-bipyridyl•̅ radical dimer complex (5) and [ONNO]ThIV-bipyridyl2– dianionic
dimer species (6) were obtained, respectively
<i>N</i>‑Aryloxide-Amidinate Thorium Complexes
An N-aryloxide-amidine ligand (1),
[ONNO] ligand, integrating phenoxide (PhO–) and
amidine ligands through methylene linkers, was employed in actinide
chemistry. Upon reaction of the deprotonated ligand with ThCl4(DME)2 in ether, the corresponding dimer complex 2 was obtained. Upon treatment of 2 with KCp*
(Cp* = Cp(Me)5) in tetrahydrofuran, the corresponding {[ONNO]ThIVCp*(LiCl)}2 (4) was obtained. In
complex 2, the two ArO– arms bonded
from the same ligand to different ThIV centers. In contrast,
both ArO– arms coordinated to the same metal center
in 4. Notably, when a mixture of 2 and bipyridine
was treated with one or two equiv of KC8, the [ONNO]ThIV-bipyridyl•̅ radical dimer complex (5) and [ONNO]ThIV-bipyridyl2– dianionic
dimer species (6) were obtained, respectively