A new family of heterometallic catalysts based on trimetalated macrocyclic tris(salen) ligands and rare-earth metals was prepared and structurally characterized. The LaZn system containing anionic ligands such as acetate plays a critical role in catalyzing the alternating copolymerization of cyclohexene oxide (CHO) and CO with a high proportion of carbonate linkages. Among the lanthanide metals, the CeZn system exhibits high catalytic activity with a turnover frequency (TOF) of over 370 h . NMR analysis of the complex and end-group analysis of the polymer suggest that the acetate ligands are rapidly exchanged, not only among coordinated acetates, but also between coordinated acetates and added carboxylate anions. These unique properties make this the first example of telomerization for the copolymerization of CHO and CO .
Hydrogenation of the neutral bis(allyl) complexes of the early lanthanides [Ln(Me3TACD)(η3‐C3H5)2] [(Me3TACD)H = 1,4,7‐trimethyl‐1,4,7,10‐tetraazacyclododecane, Me3[12]aneN4] with phenylsilane gave the tetranuclear octahydrido complexes [Ln(Me3TACD)(μ‐H)2]4 [Ln = Ce (1‐Ce), Pr (2‐Pr)] or the dinuclear allyl/hydrido complexes [Ln(Me3TACD)(η3‐C3H5)(μ‐H)]2 [Ln = Nd (3‐Nd), Sm (4‐Sm)], which were isolated and characterized. The structures of 1‐Ce and 2‐Pr are constructed of a tetrahedral Ln4H8 core. Single‐crystal X‐ray diffraction analyses of 3‐Nd and 4‐Sm revealed a C2 symmetric planar Ln2H2 core. The experimental structures agreed with the results of DFT calculations, which predict that the nuclearity of the dihydrido complexes depend on the ionic radius of the metal. Compounds 1‐Ce, 2‐Pr, 3‐Nd and 4‐Sm were tested as catalysts in the copolymerization of cyclohexene oxide with CO2 to give highly carbonate‐linked copolymers with moderate activities.
The recently published synthesis of the presumably daltonide phase InFe3N has been re‐investigated. A two‐step ammonolysis reaction gives access to the phase‐pure berthollide InxFe4–xN (0 ≤ x ≤ 0.8), which adopts a perovskite‐like structure in space group Pm$\bar{3}$m. There is a Vegard‐type behavior of the lattice parameter over the entire compositional range, and a similar trend is found for the magnetic saturation moment, which decreases while the indium content increases. Susceptibility measurements and hysteretic loops (10 K, 290 K) evidence that In0.8Fe3.2N is a ferromagnetic nitride.
Eine neue Familie von Heterometallkatalysatoren auf Basis von dreifach metallierten makrocyclischen Tris-(salen)-Liganden und Seltenerdmetallen wurde hergestellt und strukturell charakterisiert. Das LaZn 3 -System mit seinen anionischen Liganden wie Acetat spielt eine zentrale Rolle bei der katalysierten alternierenden Copolymerisation von Cyclohexenoxid (CHO) und CO 2 und liefert ein Produkt mit einem hohen Gehalt an Carbonatverknüpfungen. Bei den Lanthanoiden zeigt das CeZn 3 -System eine hohe katalytische Aktivität mit einer Wechselzahl (TOF) von über 370 h À1 .D ie NMRspektroskopische Analyse des Komplexes und die Bestimmung der Endgruppen im Polymer weisen auf einen schnellen Austausch der Acetatliganden hin. Die koordinierten Acetate werden nicht nur untereinander,sondern auchgegen zugesetzte Carboxylat-Anionen ausgetauscht. Mit solch einzigartigen Eigenschaften ist dieses System das erste Beispiel füre ine als Telomerisierung ablaufende Copolymerisation von CHO und CO 2 .
Polyurethanes (PUs)
are widely used in many applications due to
their versatile chemical and physical properties. To meet the increasing
demands on PU with respect to intrinsic mechanical and thermal properties,
they can be modified with thermally stable aromatic imide structures
to form poly(urethane imide) (PUI). However, the preparation of PUI
materials has been limited by the need for strong polar solvents,
which hinder their industrial scale development. In this work, we
prepared imide-containing isocyanate-terminated prepolymers via the
reaction of polymeric aromatic or aliphatic isocyanates and pyromellitic
dianhydride in completely solvent-free conditions. The subsequent
PUI elastomers made from these prepolymers exhibited enhanced char
formation and stiffness in comparison to the reference elastomers
without imide structures, among which the aromatic PUI elastomer shows
improved flame retardancy according to the initial cone calorimetry
measurement. This work demonstrates the potential use of imide prepolymers
in other PU applications where high thermal stability and flame retardancy
are required. The solvent-free synthesis also paves a way for the
large-scale production of PUI materials.
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