New Chromium(III) Complexes with Imine−Cyclopentadienyl Ligands: Synthesis, Characterization, and Catalytic Properties for Ethylene Polymerization

Abstract

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.

Achiral Cs-Symmetric Half-Sandwich Scandium(III) Complexes with Imine–Cyclopentadienyl Ligands Catalyze Isotactic Polymerization of 1-Hexene

“…The free ligands 2-(ArNCH)C 6 H 4 Me 4 CpH (Ar = 2,6- i Pr 2 C 6 H 3 ( La H), 2,6-Et 2 C 6 H 3 ( Lb H), 2,6-Me 2 C 6 H 3 ( Lc H)) were synthesized as reported previously . They can be deprotonated by treatment with BuLi to give the corresponding lithium salts 2-(ArNCH)C 6 H 4 Me 4 CpLi (Ar = 2,6- i Pr 2 C 6 H 3 ( La Li), 2,6-Et 2 C 6 H 3 ( Lb Li), 2,6-Me 2 C 6 H 3 ( Lc Li)).…”

New Titanium(IV) Complexes with 2-Cyclopentadienylbenzylamido Ligands: Synthesis, Characterization, and Catalytic Properties for Ethylene Polymerization and Copolymerization with 1-Hexene

“…The free ligands 2-Me 4 CpHC 6 H 4 CH 2 (R)NH (R = i Pr (H 2 L1 ), Cy (H 2 L2 ), n Pr (H 2 L3 ), 4-MePh (H 2 L4 )) were synthesized in high yields (about 60–70%) by a two-step procedure: a condensation reaction of 2-(tetramethylcyclopentadienyl)benzaldehyde with the corresponding amine derivatives followed by reduction of the formed imine compounds with LiAlH 4 , as illustrated in Scheme . The imine compounds were directly reduced in aprotic solvent (Et 2 O or THF) without isolation due to their poor stability.…”

“…CH 2 Cl 2 and 1-hexene were purified by distilling over calcium hydride before use. 2-(Tetramethylcyclopentadienyl)benzaldehyde and Ph 3 CB(C 6 F 5 ) 4 were prepared according to literature procedures. Polymerization grade ethylene was further purified by passage through columns of 5 Å molecular sieves and MnO.…”

Further studies on the effects of substituents at the Cp and salicyladiminato ligands of half-sandwich chromium(III) complexes on their catalytic properties for ethylene polymerization

“…Crystals suited for X-ray analysis grew from the mixture of CH 2 Cl 2 and hexane (20 ml, CH 2 Cl 2 /Hexane ¼ 1:5) after several days at room temperature. Elemental analyses: calcd for C 20 …”