Iminoimidazole‐based Co(II) and Fe(II) complexes: Syntheses, characterization, and catalytic behaviors for isoprene polymerization

Abstract

A stereoselectivity switchable polymerization of isoprene has been developed, which is catalyzed by iminoimidazole‐Co(II) and ‐Fe(II) complexes. The influence of substituents ranging from electron donating to the electron withdrawing on the iminoimidazole‐Co(II) and ‐Fe(II) catalysts is investigated for isoprene polymerization. Two sets of iminoimidazole‐Co(II) and ‐Fe(II) complexes have been prepared and fully characterized. X‐ray crystallography analysis reveals that the complexes Co1 and Fe1 adopt distorted tetrahedral geometries. In the presence of AlEt2Cl as co‐catalyst, all the Co(II) complexes are active and the catalytic activity is highly dependent on the molar ratio of Al/Co. All the Co(II) complexes exhibit higher activities at low Al/Co ratio. Compared with the Co(II) complexes, the Fe(II) complexes are essentially inactive under the identical condition. However, on activation with combination of AlEtCl2 and [Ph3C][B(C6F5)4], both Co(II) and Fe(II) complexes display high activities with good conversions of isoprene (up to >99%). Additionally, low molecular weight and high trans‐1,4‐unit (>96%) selectivity are characteristics of the resultant polyisoprene. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 767–775

Highly Active Iminopyridyl Iron-Based Catalysts for the Polymerization of Isoprene

“…The performance of the catalytic systems was shown to depend on the nature of the substituent carried by the pyridine ring and the N -amine group of the aminopyridyl ligand, with the complex bearing R = CH(Ph) 2 and R 1 = H showing a very high activity of TOF > 28,000 h −1 . In parallel, it is worth mentioning that related iron-based pre-catalysts supported by iminoimidazole [29] or 2-( N -arylcarboximidoylchloride)-quinoline [30] were also assessed for the polymerization of isoprene.…”

Enhancing Thermal Stability in Aminopyridine Iron(II)-Catalyzed Polymerization of Conjugated Dienes

“…For the framework of [N, N] bidentate ligands, researchers found that not only the ligand skeleton but also the hybridization of the nitrogen atom displayed significant effects on activity and selectivity of isoprene polymerization (Chart ). For example, a seminal report by Porri’s group utilizes a symmetric bipyridine iron complex, to produce high 3,4-polyisoprene with high activities in 2002, in which the hybridized nitrogen atoms are all sp 2 . Later, Ritter, Chen, and other groups designed a novel iminopyridine iron complex, where the hybridized nitrogen atoms (sp 2 , sp 2 ) are symmetric but ligand structures are unsymmetric, producing low to moderate 3,4-polyisoprene with high molecular weights .…”

Highly active and thermo‐stable iminopyridyl vanadium oxychloride catalyzed isoprene polymerization

“…[ 33 ] Recently, iminopyridine ligands have attracted significant interest because of their easy preparation, and thus are widely used in transition metal catalyzed reactions. [ 34–41 ] In the present study, various alkyl‐ and aryl‐substituted novel iminopyridine vanadium complexes were synthesized and studied their catalytic capacity for isoprene polymerization. The effects of polymerization conditions and ligand moiety on the catalytic activity, regioselectivity, and properties of polymer were investigated in detail.…”