135616-40-9Relevant articles and documents
Revised interpretation for N-cyclohexylmaleimide polymerization in the presence of an optically active cobalt(II) complex: Polymerization mediated by anionic species formed through monomer-Co(II) complex-O2 interaction
Nakano, Tamaki,Yade, Tohru,Okamoto, Yoshio
, p. 3498 - 3504 (2003)
This report revises the interpretations of the reaction mechanism in the polymerization of N-cyclohexylmaleimide (CHMI) in the presence of α,α′-azobis(isobutyronitrile) (AIBN) and (R,R)-N,N′-bis (3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminatocobalt(II) (1) [Macromolecules 2000, 33, 1489]. Although we proposed that the reaction was mediated by a radical species and that the interaction between growing polymer radical with 1 induced chirality in the main chain in the earlier report, the results in the present article indicate that the systems reported in the earlier report were most probably contaminated by a small amount of air and that the polymerization proceeds via an anionic species that was produced by the interaction of the monomer, 1, and O2. The effect of the contamination was overlooked due to the lack of a control experiment using O2 in the absence of AIBN in our earlier study. In this work, the polymerization of CHMI was performed in the presence and absence of 1, O2, αα′-azobis-(isobutyronitrile) (AIBN), and protonic additives (methanol and acetic acid). The results indicated the following: (1) the polymerization in a tetrahydrofuran-pyridine mixture occurs in the presence of 1 and a small amount of oxygen even without using AIBN; (2) the reaction does not take place in the presence of 1 alone or in the presence of 1 and AIBN under a strictly controlled N2 atmosphere; (3) a small amount of AcOH completely inhibits the polymerization with 1 and O2 while 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) does not kill the reaction; and (4) the polymer was likely to possess -OH or -OOH groups at the chain terminals (a telechelic structure). On the basis of these observations, we withdraw our earlier, wrong interpretation that the polymerization is mediated by a radical species and conclude that the polymerization and the observed stereochemistry are effected by an anionic mechanism.
Olefin polymerization promoted by a stereorigid bridged diiminobis(phenolate) zirconium complex
Cuomo, Cinzia,Strianese, Maria,Cuenca, Tomas,Sanz, Martial,Grassi, Alfonso
, p. 7469 - 7476 (2004)
Two diiminobis(phenolate) zirconium complexes [C6H 10-{N=CH-(3,5-tBu2C6H 2-2-O)-kO}2]-ZrX2 [X = CH2Ph (1), Cl (3)] have been synthesized and characterized by NMR solution spectroscopy. Complex 1 was found conformationally stable and isolated in the octahedral C2 symmetric form. When exposed to the light in hydrocarbon solution, 1 readily undergoes to 1,2 benzyl migration converting the diiminobis(phenolate) ligand in the corresponding benzylamidoiminobis(phenolate) . Complex 3 is more thermally stable and found in slow equilibrium between the cis-α and cis-β forms with the former largely prevalent (9:1 molar ratio). The rate of interconversion between the two diastereoisomers was estimated in 3.6 × 10-1 s-1 by NMR exchange spectroscopy (EXSY). 1 and 3 are active ethylene polymerization catalysts after reaction with MAO or [CPh3] [B(C6F5) 4]/Al-iBu3. The polydispersity index of polyethylene produced by 1 is about 2, suggesting the presence of a single active species and that the symmetry of the precatalyst is retained during polymerization. The catalyst is stable over 3 h, and the polymerization activity linearly increases with time. Copolymers of ethylene with propylene or 1-hexene were synthesized, and the 13C NMR analysis of their microstructure suggested the highly regioregular 1,2 insertion of the 1-olefin and the inability of the ligand environment to express stereochemical control during monomer insertion.
Diastereomerically-specific zirconium complexes of chiral salan ligands: Isospecific polymerization of 1-hexene and 4-methyl-1-pentene and cyclopolymerization of 1,5-hexadiene
Yeori, Adi,Goldberg, Israel,Shuster, Michael,Kol, Moshe
, p. 13062 - 13063 (2008/02/08)
Chiral Salan ligands were found to wrap in a highly diastereoselective manner around zirconium leading to C2-symmetric complexes of predetermined chirality at the metal. These complexes led to active polymerization of higher olefins, their activity and is
A practical one-pot synthesis of enantiopure unsymmetrical salen ligands
Holbach, Michael,Zheng, Xiaolai,Burd, Caroline,Jones, Christopher W.,Weck, Marcus
, p. 2903 - 2906 (2007/10/03)
A practical, one-pot synthesis of enantiopure unsymmetrical salen ligands is described, using a 1:1:1 molar ratio of a chiral diamine and two different salicylaldehydes. The new synthetic protocol can be readily performed in good yields (60-85%) on a mult
