No abstract

Unchelated scandium(III) trichloride complexes, 2-(ArNCH)C 6 H 4 Me 4 CpScCl 3 Li(THF) 4 (Ar = 2,6-i Pr 2 C 6 H 3 (1a), 2,6-Et 2 C 6 H 3 (1b), 2,6-Me 2 C 6 H 3 (1c)), were obtained from the reaction of ScCl 3 (THF) 3 with the lithium salt of the corresponding ligand, 2-(ArC 6 H 3 N CH)C 6 H 4 Me 4 CpLi, in THF. After heating at 120 °C under vacuum for 30 min, the attached LiCl and THF were removed from complexes 1 to give the chelated scandium(III) dichloride complexes 2-(ArNCH)C 6 H 4 Me 4 CpScCl 2 ([Ar = 2,6-i Pr 2 C 6 H 3 (2a), 2,6-Et 2 C 6 H 3 (2b), 2,6-Me 2 C 6 H 3 (2c)). Attempts to synthesize dialkyl scandium(III) complexes by the reaction of Sc(CH 2 SiMe 3 ) 3 (THF) 2 with the corresponding free ligands were not successful. The scandium(III) trialkyl complex 2-[Li(THF) 3 (2,6-i Pr 2 C 6 H 3 )NCH]C 6 H 4 Me 4 CpSc-(CH 2 SiMe 3 ) 3 (3) was synthesized by a one-pot reaction of ScCl 3 (THF) 3 with 2-(2,6-i Pr 2 C 6 H 3 NCH)C 6 H 4 Me 4 CpLi and 3 equiv of Me 3 SiCH 2 Li in THF sequentially. The scandium(III) dialkyl complex 2-(2,6-i Pr 2 C 6 H 3 NCH)C 6 H 4 Me 4 CpSc-(CH 2 SiMe 3 ) 2 ( 4) was obtained from the reaction of the dichloride complex 2a with 2 equiv of Me 3 SiCH 2 Li in hexane. Complexes 1b,c were directly converted to complexes 2b,c without purification and characterization. All other scandium(III) complexes were characterized by 1 H and 13 C NMR spectroscopy and elemental analyses. The structures of complexes 1a, 2c, 3, and 4 were determined by single-crystal X-ray crystallography, which indicates that the imine N atoms in complexes 1a and 3 do not coordinate to the central scandium atoms. Complexes 2a−c and 4 were found to exhibit moderate catalytic activity for propylene and 1-hexene polymerization upon activation with AlR 3 /Ph 3 CB(C 6 F 5 ) 4 or methylaluminoxane (MAO) and produce atactic polypropylene and isotactic poly(1-hexene). The effects of molecular structures and reaction conditions on the catalytic behavior of these complexes were examined and the possible catalytic mechanism was discussed.

The density peaks clustering (DPC) is known as an excellent approach to detect some complicated-shaped clusters with high-dimensionality. However, it is not able to detect outliers, hub nodes and boundary nodes, or form low-density clusters. Therefore, halo is adopted to improve the performance of DPC in processing low-density nodes. This paper explores the potential reasons for adopting halos instead of low-density nodes, and proposes an improved recognition method on Halo node for Density Peak Clustering algorithm (HaloDPC). The proposed HaloDPC has improved the ability to deal with varying densities, irregular shapes, the number of clusters, outlier and hub node detection. This paper presents the advantages of the HaloDPC algorithm on several test cases.

New half-metallocene chromium complexes with a coordinated secondary amine side-arm were synthesized and studied as catalysts for olefin polymerization.

A series of new half-sandwich chromium(III) complexes chelated with (2-((arylimino)methyl)phenyl)tetramethylcyclopentadienyl ligands, 2-(ArNCH)C6H4Me4CpCrCl2 (Ar = 2,6-Me2C6H3 (1), 2,6-Et2C6H3 (2), 2,6- i Pr2C6H3 (3), 4-MeC6H4 (4)), have been synthesized from the reaction of CrCl3 with the lithium salt of the corresponding ligand 2-(ArNCH)C6H4Me4CpLi (Ar = 2,6-Me2C6H3 (LiL 1), 2,6-Et2C6H3 (LiL 2), 2,6- i Pr2C6H3 (LiL 3), 4-MeC6H4 (LiL 4)). Free ligands HL 1−HL 4 were prepared by the condensation reaction of 2-(tetramethylcyclopentadienyl)benzaldehyde with 2,6-dialkylaniline. The free ligands were characterized by 1H NMR spectroscopy, while the chromium(III) complexes were characterized by elemental analyses and single-crystal X-ray crystallography. The X-ray crystallographic analysis indicates that the imine N atom in these complexes coordinates to the central chromium atom. Upon activation with AlR3 and Ph3CB(C6F5)4, these complexes exhibit high catalytic activity for ethylene polymerization and produce polyethylene with moderate to high molecular weights. These chromium(III) complexes can also be activated with AlR3 alone. In the latter case, they show slightly lower catalytic activity for ethylene polymerization in comparison to the AlR3/Ph3CB(C6F5)4 activated catalyst systems. The effects of ligand structure, polymerization temperature, AlR3, and Al/Cr molar ratio on the catalytic behavior of these complexes were examined.