Search

Stoichiometric reactions of YCl3(THF)3withpotassium 2-((arylimino)methyl)quinolin-8-olates or 2-(1-(arylimino)ethyl)quinolin-8-olatesin THF solution gave the mononuclear LYCl2(DMSO)2complexes 1–5in the presence ofDMSO and a representative dinuclear complex 6in theabsence of DMSO. All yttrium complexes were fully characterized byNMR measurements and elemental analysis, and the crystal structuresof complexes 1and 4–6were determined by single-crystal X-ray diffraction. The structuresindicate coordination number seven around the yttrium center and pentagonalbipyramidal geometries. The complexes all feature diapical YCl2moieties and one tridentate organic ligand in the equatorialplane. Upon reaction of the yttrium precatalysts 1–6with LiCH2Si(CH3)3aloneor with LiCH2Si(CH3)3together withBnOH, the ring-opening polymerization (ROP) of ε-caprolactone(ε-CL) occurred with high efficiency. Depending on conditions,the ROP of ε-CL produced polycaprolactone with narrow moleculardistribution and in a living manner. Theoretical studies of the chlorine/CH2SiMe3and Me3SiCH2/BnO ligandexchange reactions suggest that the replacement of the apical ligandscan proceed without significantly affecting the equatorial ligands.These results suggest that one of the apical Y–CH2SiMe3bonds within the LY(CH2SiMe3)2intermediate catalyzes the polymerization in the BnOH-freeprocess. Most polymers generated by BnOH-assisted catalysis possess Mnvalues that are similar to Mn,calvalues based on Y–OBn, suggesting that oneapical Y–OBn bond of the diapical LY(OBn)(CH2SiMe3) intermediate catalyzes most or all of the ring polymerizationof ε-CL. [ABSTRACT FROM AUTHOR]

To gain a deeper knowledge of the nature of the species formed in situ by reaction of a catalyst precursor complex and typical cocatalysts used for ethylene oligomerization or polymerization, the Cr(III) complex fac-[Cr(NPN)Cl3] (1; NPN = bis(2-picolyl)phenylphosphine) was reacted with MAO and partial methylation to give the mononuclear complex fac-[Cr(NPN)Cl2.23Me0.77] (2) was observed, whereas reaction with AlMe3in toluene led to partial halide abstraction and produced the dinuclear, chloride-bridged dicationic complex [{fac-Cr(NPN)Me(μ-Cl)}2][AlMexCl4–x]2(3·[AlMexCl4–x]2), in which the metal centers are bridged by two chloride ligands. The complex fac-[Cr(NPN)Cl2Et] (4) was isolated in high yield from the reaction of 1with AlEt3and contains a rare example of CrIII–Et function. Upon treatment of 1with EtAlCl2, the dinuclear Cr(III) complex [{fac-Cr(NPN)}2(μ-Cl)3][AlCl4]3(5·[AlCl4]3) was obtained, which contains three bridging chlorides. Thus, under the conditions investigated, MAO and AlEt3behaved as alkylation agents, whereas AlMe3and EtAlCl2reacted as cationization agents. On activation with MAO and under comparable conditions, 1–5exhibited similar catalytic properties, with activities between 2700 and 2800 g of C2H4/((g of Cr) h), but the major oligomer produced using the 4/MAO system was 1-decene. The neutral alkyl complexes 2and 4and the cationic complexes 3and 5did not exhibit catalytic activity for ethylene oligomerization in the absence of MAO. The structures of the complexes 2, 3·[AlMexCl4–x]2, 4, and 5·[AlCl4]3have been determined by single-crystal X-ray diffraction. [ABSTRACT FROM AUTHOR]

A correction is presented to the article "Synthesis, Characterization, and Heterobimetallic Cooperation in a Titanium−Chromium Catalyst for Highly Branched Polyethylenes," by Shaofeng Liu, Alessandro Motta, Massimiliano Delferro, and Tobin J. Marks from volume 135, 2013.