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 bis­(trimethyl)­silylamide 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 5f¹‑4f^<i>n</i> Complexes

The heterobimetallic complexes [{UO₂Ln­(py)₂(L)}₂], 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 [UO₂(py)­(H₂L)] by the rare-earth complexes Ln^III(A)₃ (A = N­(SiMe₃)₂, OC₆H₃Bu^t₂-2,6) 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)₃LiOUO­(μ-X)­Ln­(py)­(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 U₂O₂ diamond core with shorter uranyl UO distances than in the monomeric complexes. The synthesis by Ln^III–A homolysis allows [5f¹-4f^<i>n</i>]₂ and Li­[5f¹-4f^<i>n</i>] complexes with oxo-bridged metal cations to be made for all possible 4f^<i>n</i> 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^VSm^III monomer, whereas the dimeric U^VDy^III 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 5f¹‑4f^<i>n</i> Complexes

The heterobimetallic complexes [{UO₂Ln­(py)₂(L)}₂], 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 [UO₂(py)­(H₂L)] by the rare-earth complexes Ln^III(A)₃ (A = N­(SiMe₃)₂, OC₆H₃Bu^t₂-2,6) 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)₃LiOUO­(μ-X)­Ln­(py)­(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 U₂O₂ diamond core with shorter uranyl UO distances than in the monomeric complexes. The synthesis by Ln^III–A homolysis allows [5f¹-4f^<i>n</i>]₂ and Li­[5f¹-4f^<i>n</i>] complexes with oxo-bridged metal cations to be made for all possible 4f^<i>n</i> 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^VSm^III monomer, whereas the dimeric U^VDy^III complex was found to show magnetic bistability at 3 K, a property required for the development of single-molecule magnets