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Published in Joseph C. Salamone, Polymeric Materials Encyclopedia, 2020
The molecular weight distribution (MWD) of these polymers are narrow, nearly equal to two. This indicates a homogeneous polymerization. Catalytic activities of halfmetallocene such as cyclopentadienyltitanium trichloride (CpTiCl3), pentamethylcyclopentadienyltitanium trichloride (Cp*TiCl3) are greater than that of bent-metallocene, such as Cp2TiCl2, Cp *2TiCl2. Molecular weight of a polymer is controlled by means of not only polymerization temperature, but also Ti-ligand species. The influence of an σ-ligand on the variation of molecular weight is small in comparison with that of π-ligands. It suggests that the properties of the active sites from the reaction of a titanium compound having only an σ-ligand with MAO are similar to each other.
Structural variations in cyclopentadienyl uranium(III) iodide complexes
Published in Journal of Coordination Chemistry, 2020
Justin C. Wedal, Cory J. Windorff, Daniel N. Huh, Austin J. Ryan, Joseph W. Ziller, William J. Evans
Complex 1 (Figure 1) is the product if the ionic metathesis eliminates the KI byproduct cleanly. It is a classic monometallic uranium bent metallocene with two terminal ligands in the wedge formed by the rings. In the absence of THF that coordinates to the uranium center, KI is incorporated into the final product. Compound 2 (Figure 2) is much more complicated than 1 in that it incorporates one equivalent of KI per uranium and crystallizes as a dimer with two metallocene units connected by doubly- and triply-bridging iodide ligands. The second half of the molecule is generated by a crystallographic inversion center at the center of the two potassium atoms and the two µ3–I atoms. Complex 2 contains the “(C5Me5)2U(µ–X)2M(solvent)n” (X = halide, M = alkali metal) “ate-salt” motif that is commonly seen with THF solvating the alkali metal cation [14–16], but is also observed with Et2O [17–21]. In this case, the “(C5Me5)2U(µ–I)2K(Et2O)2” unit does not crystallize alone, but as a dimer. The 1H and 13C NMR spectra of 2 are consistent with retention of the Et2O molecules in solution.