22 research outputs found

    Mechanistic Studies of Redox-Switchable Copolymerization of Lactide and Cyclohexene Oxide by a Zirconium Complex

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    Several aspects of the copolymerization of l-lactide (LA) and cyclohexene oxide (CHO) by a redox-switchable zirconium catalyst, (salfan)­Zr­(O<sup><i>t</i></sup>Bu)<sub>2</sub> (salfan = 1,1′-bis­(2-<i>tert</i>-butyl-6-<i>N</i>-methylmethylenephenoxy)­ferrocene), were examined, such as the mechanism of cyclohexene oxide polymerization, the reactivity of [(salfan)­Zr­(O<sup><i>t</i></sup>Bu)<sub>2</sub>]­[BAr<sup>F</sup>] (BAr<sup>F</sup> = tetrakis­(3,5-bis­(trifluoromethyl)­phenyl)­borate) toward lactide, and comonomer effects on polymerization rates. Experimental methods and DFT calculations indicate that the likely mechanism of CHO polymerization by [(salfan)­Zr­(O<sup><i>t</i></sup>Bu)<sub>2</sub>]­[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)­Zr­(O<sup><i>t</i></sup>Bu)<sub>2</sub>]­[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

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    The synthesis, characterization, and reactivity of an aluminum alkoxide complex supported by a ferrocene-based ligand, (thiolfan*)­Al­(O<sup><i>t</i></sup>Bu) (<b>1</b><sup><b>red</b></sup>, thiolfan* = 1,1′-di­(2,4-di-<i>tert</i>-butyl-6-thiophenoxy)­ferrocene), 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

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    Four types of alkenyl organocopper­(I) aggregates linked by 1,3-butadienyl and/or 1,3,5,7-octatetraenyl moieties were selectively realized in good isolated yields. All these organocopper­(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 organocopper­(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

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    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

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    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

    No full text
    Four types of alkenyl organocopper­(I) aggregates linked by 1,3-butadienyl and/or 1,3,5,7-octatetraenyl moieties were selectively realized in good isolated yields. All these organocopper­(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 organocopper­(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

    No full text
    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

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    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

    No full text
    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
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