The development of homogeneous metal catalysts with high activity and high thermal stability is vital for the synthesis of polyolefin elastomers (POEs) in solution-phase olefin polymerization processes. In this contribution, the stoichiometric reactions of 8-(2,6-(R 1 ) 2 -4-R 2 -anilide)-5,6,7-trihydroquinoline (1−3; 1, R 1 = i

In order to examine the possibility to promote cooperative effects on catalytic activity and selectivity in ethylene dimerization through ligand design, the bisphosphino-iminato ligands syn- L and anti- L were prepared to support the dinuclear nickel complexes syn -Ni 2 and anti- Ni 2 . The Ni centers are successfully locked in relatively close proximity in syn- Ni 2 (6.433(5) Å) but are much farther apart in anti- Ni 2 because of the rigid anthracene skeleton. The mononuclear complex [NiBr2(C14H9-NCH-C6H4-2-PPh2)] (Ni 1 ) was also prepared for control experiments. In the presence of EtAlCl2, syn -Ni 2 showed a remarkably high activity for ethylene dimerization (>90%) (up to 9.10 × 106 g (mol of Ni)−1 h–1), which is approximately 1.5- and 3.3-fold higher, respectively, than those of anti- Ni 2 or of mononuclear Ni 1 . The redox properties of dinuclear complexes were studied by cyclic voltammetry (CV) and their comparison with those of the mononuclear complex indicates the possible existence of cooperativity between the two metal centers in the dinuclear structures. Although a detailed mechanism has not been elucidated, cooperative effects favor the isomerization of 1-butene, and dinuclear syn- Ni 2 and anti- Ni 2 exhibited higher selectivity for 2-butene in comparison to mononuclear Ni 1 under otherwise identical reaction conditions.

Ultrahigh molecular weight polyethylene (UHMWPE) is a class of high-performance engineering plastics, exhibiting a unique set of properties and applications. Although many advances have been achieved in recent years, the synthesis of UHMWPE is still a great challenge. In this contribution, a series of zirconium and hafnium complexes, [2,6-(R1)2-4-R2-C6H2-N-C(camphyl)=C(camphyl)-N-2,6-(R1)2-4-R2-C6H2]MMe2(THF) (1-Zr: R1 = Me, R2 = H, M = Zr; 2-Zr: R1 = Me, R2 = Me, M = Zr; 1-Hf: R1 = Me, R2 = H, M = Hf; 2-Hf: R1 = Me, R2 = Me, M = Hf), bearing bidentate NN ligands with the bulky camphyl backbone were synthesized by the stoichiometric reactions of α-diimine ligands with MMe4 (M = Hf or Zr). All Zr and Hf metal complexes were analyzed using 1H and 13C NMR spectroscopy, and the molecular structures of complexes 1-Zr and 1-Hf were determined by single-crystal X-ray diffraction, revealing that the original α-diimine ligand was selectively reduced into the ene-diamido form and generated an 1,3-diaza-2-metallocyclopentene ring in the metal complexes. Zr complexes 1-Zr and 2-Zr showed moderate activity (up to 388 kg(PE)·mol−1(M)·h−1), poor copolymerization ability, but unprecedented molecular weight capability toward ethylene/1-octene copolymerization. Therefore, copolymers with ultrahigh molecular weights (> 600 or 337 × 104 g∙mol−1) were successfully synthesized by 1-Zr or 2-Zr, respectively, with the borate cocatalyst [Ph3C][B(C6F5)4]. Surprisingly, Hf complexes 1-Hf and 2-Hf showed negligible activity under otherwise identical conditions, revealing the great influence of metal centers on catalytic performances.