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Reactions of 2,6-(ArNCH)2C6H3Li with CrCl2(THF)2afford two trinuclear bis(imino)aryl NCN pincer Cr(II) complexes {[2,6-(ArNCH)2C6H3]Cr(μ-Cl)2}2Cr [Ar = 2,6-Me2C6H3(1a), 2,6-Et2C6H3(1b)], and a mononuclear bis(imino)aryl NCN pincer Cr(II) complex [2,6-(ArNCH)2C6H3]Cr(μ-Cl)2Li(THF)2[Ar = 2,6-iPr2C6H3(1c)], respectively. Similar reactions of 2,6-(ArNCH)2C6H3Li with CrCl3(THF)3produce only mononuclear bis(imino)aryl NCN pincer Cr(III) complexes [2,6-(ArNCH)2C6H3]CrCl2(THF) [Ar = 2,6-Me2C6H3(2a), 2,6-Et2C6H3(2b), 2,6-iPr2C6H3(2c)]. X-ray crystallographic analysis reveals that the terminal Cr(II) atoms in 1aand 1band the Cr(II) atom in 1cpossess a distorted trigonal bipyramidal coordination environment with the Cipsoatom of the pincer ligand and two chloride atoms in the equator and the two imine nitrogen atoms in the apical positions, while the Cr(III) complexes 2a, 2b, and 2call adopt a distorted octahedral geometry around the chromium metal. Upon activation with trialkylaluminum and [Ph3C][B(C6F5)4]−, the Cr(III) complexes show high catalytic activity for isoprene polymerization and afford polyisoprene with predominately trans-1,4 units, whereas the Cr(II) complexes are inert under the same conditions. [ABSTRACT FROM AUTHOR]

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-iPr2C6H3(3), 4-MeC6H4(4)), have been synthesized from the reaction of CrCl3with the lithium salt of the corresponding ligand 2-(ArNCH)C6H4Me4CpLi (Ar = 2,6-Me2C6H3(LiL1), 2,6-Et2C6H3(LiL2), 2,6-iPr2C6H3(LiL3), 4-MeC6H4(LiL4)). Free ligands HL1−HL4were 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 AlR3and 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 AlR3alone. In the latter case, they show slightly lower catalytic activity for ethylene polymerization in comparison to the AlR3/Ph3CB(C6F5)4activated catalyst systems. The effects of ligand structure, polymerization temperature, AlR3, and Al/Cr molar ratio on the catalytic behavior of these complexes were examined. [ABSTRACT FROM AUTHOR]

The tridentate ligand N-(2-((2,6-diisopropylphenylimino)methyl)phenyl)quinolin-8-amine ( HL) was prepared. Treatment of HLwith 1 equiv of Ln(CH 2SiMe 3) 3(THF) 2afforded the corresponding rare-earth metal bis(alkyl) complexes LLn(CH 2SiMe 3) 2(THF) n(Ln = Sc, n= 0 ( 1); Y, n= 1 ( 2); Lu, n= 0 ( 3)) in high yields. Variable-temperature 1H NMR spectral analysis showed that these complexes were fluxional at room temperature. Complexes 1and 3were THF-free, where the metal center adopted a square-pyramidal geometry, while in 2the metal center generated a distorted octahedral geometry owing to the coordination of a THF molecule. All these complexes catalyzed the ring-opening polymerization of ε-caprolactone with high activities in living fashion, among which the Lu complex was proved to be more active than its Sc and Y analogues. [ABSTRACT FROM AUTHOR]

The first aryldiimine NCN-pincer ligated rare earth metal dichiorides (2,6-(2,6-C6H3R2N=CH)2-C6H3)LnCl2(THF)2 (Ln = Y, R = Me (1), Et (2), iPr (3); R = Et, Ln = La (4), Nd (5), Gd (6), Sm (7), Eu (8), Tb (9), Dy (10), Ho (11), Yb (12), Lu (13)) were successfully synthesized via transmetalation between 2,6-(2,6-C6H3-R2N=CH)2-C6H3Li and LnCl3(THF)1~3.5. These complexes are isostructural monomers with two coordinating THF molecules, where the pincer ligand coordinates to the central metal ion in a κC:κN:κN′ tridentate mode, adopting a meridional geometry. Complexes 1-6, 9-11, and 13 combined with aluminum tris(alkyl)s and [Ph3C][B(C6F5)4] established a homogeneous Ziegler-Natta catalyst system, which exhibited high activities and excellent cis-1,4 selectivities for the polymerizations of butadiene (Tp = 25 °C, 99.9%; 0 °C, 100%) and isoprene (T~ = 25 °C, 98.8%). Remarkably, such high cis-1,4 selectivity almost remained at elevated polymerization temperatures up to 80 °C and did not vary with the type of the central lanthanide element, however, which was influenced obviously by the ortho substituent of the N-aryl ring of the ligands and the bulkiness of the aluminum alkyls. The Ln-Al bimetallic cations were considered as the active species. These results shed new light on improving the catalytic performance of the conventional Ziegler-Natta catalysts for the specific selective polymerization of dienes. [ABSTRACT FROM AUTHOR]

Lipase-catalyzed terpolymerizations were performed with the monomers trimethylolpropane (B3), 1,8-octanediol (B2), and adipic acid (A2). Polymerizations were performed in bulk, at 70 °C, for 42 h, using immobilized lipase B from Candida antartica(Novozyme-435) as a catalyst. To determine the substitution pattern of trimethylolpropane (TMP) in copolymers, model compounds with variable degrees of acetylation were synthesized. Inverse-gated 13C NMR spectra were recorded to first determine the chemical shift positions for mono-, di-, and trisubstituted TMP units and, subsequently, to determine substitution of TMP units along chains. Variation of TMP in the monomer feed gave copolymers with degrees of branching (DB) from 20% to 67%. In one example, a hyperbranched copolyester with 53 mol % TMP adipate units was formed in 80% yield, with Mw14 100 (relative to polystyrene standards), Mw/Mn5.3, and DB 36%. Thermal and crystalline properties of the copolyesters were studied by thermogravimetric analysis and differential scanning calorimetry. [ABSTRACT FROM AUTHOR]

The article presents a research about the development of a highly active half-metallocene chromium(III) catalyst system for ethylene polymerization. The new catalyst system, which is activated by trialkylaluminum, represents a remarkable addition to the limited list of half-metallocene type chromium ethylene polymerization catalysts.

A series of new rare-earth metal bis(alkyl) complexes [L1−3Ln(CH2SiMe3)2(THF)n] (L1= MeC4H2SCH2NC6H4(Ph)2PNC6H2Me3-2,4,6: Ln = Sc, n= 1 (1a); Ln = Lu, n= 1 (1b); L2= MeC4H2SCH2NC6H4(Ph)2PNC6H3Et2-2,6: Ln = Sc, n= 1 (2a); Ln = Lu, n= 1 (2b); Ln = Y, n= 1 (2c); L3= MeC4H2SCH2NC6H4(Ph)2PNC6H3iPr2-2,6: Ln = Sc, n= 0 (3a)) and L4Sc(CH2SiMe3)2(THF) (4a) (L4= C6H5CH2NC6H4(Ph)2PNC6H3Et2-2,6) have been prepared by reaction of rare-earth metal tris(alkyl)s with the corresponding HL1−4ligands via alkane elimination. Complexes 1a, 1b, 2a−2c, and 4aare monomeric with a coordinating THF molecule. Each metal ion is coordinated by a NPN ligand, two trans-located alkyl groups, and a THF molecule, forming a distorted trigonal-bipyramidal geometry. Complex 3ais THF-free, adopting a distorted tetrahedron geometry. In combination with AlR3and borate, these complexes have shown medium activity and good trans-1,4 selectivity for the polymerization of butadiene. The resultant polymer has moderate molecular weight (Mn= 10 000−18 000) with narrow molecular weight distribution (Mw/Mn< 1.6) and trans-1,4 regularity varying from 49.2% up to 91.3%. The catalyst performances are strongly dependent on the orthosubstituent of the N-aryl ring and the presence of the thiophene moiety of the ligands and the type of aluminum alkyls and the lanthanide metal used. The scandium complex 2adisplays the highest trans-1,4 selectivity. [ABSTRACT FROM AUTHOR]