3 research outputs found
Effects of the Grafting of Lanthanum Complexes on a Silica Surface on the Reactivity: Influence on Ethylene, Propylene, and 1,3-Butadiene Homopolymerization
In this contribution,
we report full details of the ethylene, 1,3-butadiene,
and propylene homopolymerization processes mediated by alkylated bisÂ(trimethyl)Âsilylamide
lanthanide-grafted complexes using a density functional theory (DFT)
study of the initiation and first propagation steps. These systems
allows us (i) to examine the role of the grafting mode on the kinetics
and thermodynamics of the three processes considered, (ii) to confirm
the catalytic behavior of these grafted complexes in ethylene polymerization,
(iii) to rationalize the experimental preference for 1,4-cis polymerization
of 1,3-butadiene, and (iv) to provide unprecedented information on
the catalytic activity of the lanthanide-grafted complex as a propylene
hompolymerization catalyst
Oxo-Functionalization and Reduction of the Uranyl Ion through Lanthanide-Element Bond Homolysis: Synthetic, Structural, and Bonding Analysis of a Series of Singly Reduced Uranyl–Rare Earth 5f<sup>1</sup>‑4f<sup><i>n</i></sup> Complexes
The heterobimetallic
complexes [{UO<sub>2</sub>LnÂ(py)<sub>2</sub>(L)}<sub>2</sub>], combining
a singly reduced uranyl cation and a
rare-earth trication in a binucleating polypyrrole Schiff-base macrocycle
(Pacman) and bridged through a uranyl oxo-group, have been prepared
for Ln = Sc, Y, Ce, Sm, Eu, Gd, Dy, Er, Yb, and Lu. These compounds
are formed by the single-electron reduction of the Pacman uranyl complex
[UO<sub>2</sub>(py)Â(H<sub>2</sub>L)] by the rare-earth complexes Ln<sup>III</sup>(A)<sub>3</sub> (A = NÂ(SiMe<sub>3</sub>)<sub>2</sub>, OC<sub>6</sub>H<sub>3</sub>Bu<sup>t</sup><sub>2</sub>-2,6) via homolysis
of a Ln–A bond. The complexes are dimeric through mutual uranyl <i>exo</i>-oxo coordination but can be cleaved to form the trimetallic,
monouranyl “ate” complexes [(py)<sub>3</sub>LiOUOÂ(ÎĽ-X)ÂLnÂ(py)Â(L)]
by the addition of lithium halides. X-ray crystallographic structural
characterization of many examples reveals very similar features for
monomeric and dimeric series, the dimers containing an asymmetric
U<sub>2</sub>O<sub>2</sub> diamond core with shorter uranyl Uî—»O
distances than in the monomeric complexes. The synthesis by Ln<sup>III</sup>–A homolysis allows [5f<sup>1</sup>-4f<sup><i>n</i></sup>]<sub>2</sub> and LiÂ[5f<sup>1</sup>-4f<sup><i>n</i></sup>] complexes with oxo-bridged metal cations to be
made for all possible 4f<sup><i>n</i></sup> configurations.
Variable-temperature SQUID magnetometry and IR, NIR, and EPR spectroscopies
on the complexes are utilized to provide a basis for the better understanding
of the electronic structure of f-block complexes and their f-electron
exchange interactions. Furthermore, the structures, calculated by
restricted-core or all-electron methods, are compared along with the
proposed mechanism of formation of the complexes. A strong antiferromagnetic
coupling between the metal centers, mediated by the oxo groups, exists
in the U<sup>V</sup>Sm<sup>III</sup> monomer, whereas the dimeric
U<sup>V</sup>Dy<sup>III</sup> complex was found to show magnetic bistability
at 3 K, a property required for the development of single-molecule
magnets
Oxo-Functionalization and Reduction of the Uranyl Ion through Lanthanide-Element Bond Homolysis: Synthetic, Structural, and Bonding Analysis of a Series of Singly Reduced Uranyl–Rare Earth 5f<sup>1</sup>‑4f<sup><i>n</i></sup> Complexes
The heterobimetallic
complexes [{UO<sub>2</sub>LnÂ(py)<sub>2</sub>(L)}<sub>2</sub>], combining
a singly reduced uranyl cation and a
rare-earth trication in a binucleating polypyrrole Schiff-base macrocycle
(Pacman) and bridged through a uranyl oxo-group, have been prepared
for Ln = Sc, Y, Ce, Sm, Eu, Gd, Dy, Er, Yb, and Lu. These compounds
are formed by the single-electron reduction of the Pacman uranyl complex
[UO<sub>2</sub>(py)Â(H<sub>2</sub>L)] by the rare-earth complexes Ln<sup>III</sup>(A)<sub>3</sub> (A = NÂ(SiMe<sub>3</sub>)<sub>2</sub>, OC<sub>6</sub>H<sub>3</sub>Bu<sup>t</sup><sub>2</sub>-2,6) via homolysis
of a Ln–A bond. The complexes are dimeric through mutual uranyl <i>exo</i>-oxo coordination but can be cleaved to form the trimetallic,
monouranyl “ate” complexes [(py)<sub>3</sub>LiOUOÂ(ÎĽ-X)ÂLnÂ(py)Â(L)]
by the addition of lithium halides. X-ray crystallographic structural
characterization of many examples reveals very similar features for
monomeric and dimeric series, the dimers containing an asymmetric
U<sub>2</sub>O<sub>2</sub> diamond core with shorter uranyl Uî—»O
distances than in the monomeric complexes. The synthesis by Ln<sup>III</sup>–A homolysis allows [5f<sup>1</sup>-4f<sup><i>n</i></sup>]<sub>2</sub> and LiÂ[5f<sup>1</sup>-4f<sup><i>n</i></sup>] complexes with oxo-bridged metal cations to be
made for all possible 4f<sup><i>n</i></sup> configurations.
Variable-temperature SQUID magnetometry and IR, NIR, and EPR spectroscopies
on the complexes are utilized to provide a basis for the better understanding
of the electronic structure of f-block complexes and their f-electron
exchange interactions. Furthermore, the structures, calculated by
restricted-core or all-electron methods, are compared along with the
proposed mechanism of formation of the complexes. A strong antiferromagnetic
coupling between the metal centers, mediated by the oxo groups, exists
in the U<sup>V</sup>Sm<sup>III</sup> monomer, whereas the dimeric
U<sup>V</sup>Dy<sup>III</sup> complex was found to show magnetic bistability
at 3 K, a property required for the development of single-molecule
magnets