Abstract:Iron complexes of the types [Fe(HL)2Cl2] (Fe1: HL1 = pyridine-2-aldoxime; Fe2: HL2 = 6-methylpyridine-2-aldoxime; Fe3: HL3 = phenyl-2-pyridylketoxime; Fe4: HL4 = picolinaldehyde O-methyl oxime) were prepared and characterized by elemental analysis and IR spectroscopy. The crystal structure of Fe2, determined by single-crystal X-ray diffraction, featured a distorted octahedral coordination of the iron center binding with two ligands of HL2. The X-ray structure and infrared spectral data indicated that pyridine-… Show more
“…Moreover, the N oxime atoms of each ligand have a stronger coordination than N pyridine at the cobalt center according to the bond lengths [Co-N1 = 2.188 (17), Co-N2 = 2.098 (16), Co-N3 = 2.219 (16), Co-N4 = 2.132 (16)]. Consistent with the previous work of pyridine-oxime iron complex [65], the oxime proton is unionized. (15).…”
Section: Synthesis and Characterization Of Co(ii) Complexessupporting
confidence: 86%
“…2). However, it needs to be emphasized that the pyridine-oxime ligated iron complex bearing one 6-methyl substituent at pyridine ring showed lower activity because of steric hindrance in the previous work [65]. Zhang's group also reported that the substituent at the 6-position of the pyridine ring significantly influenced the catalytic performances of the iminopyridine ligated Co complexes.…”
Section: Polymerization Of Isoprene Catalyzed By Co(ii) Complexesmentioning
confidence: 94%
“…Ligands L1 and L3 were purchased and used directly without treatment. The ligands L2 and L4 were synthesized and characterized according to the previous report [65]. A typical procedure for the synthesis of ligand was carried out as follows.…”
Section: Co(ii) Complexes Preparationmentioning
confidence: 99%
“…Due to our ongoing burning desire to develop polymerization catalysts with high performance, we are interested in transition metal catalysts coordinating with N,N-bidentate ligands for diene polymerization [58][59][60][61][62][63][64]. In a recent piece of work, we reported that the pyridine-oxime ligand exhibited high performance in iron catalyzed isoprene polymerization with very low amount of methylaluminoxane [65]. Confirming the fundamental role played by the nature of the pyridine-oxime ligand and the type of cobalt catalyst in determining the catalytic activity and selectivity [66,67], herein we describe a series of pyridine-oxime ligated cobalt catalysts and study their catalytic properties for isoprene polymerization.…”
Several cobalt(II) complexes Co1–Co3 bearing pyridine–oxime ligands (L1 = pyridine-2-aldoxime for Co1; L2 = 6-methylpyridine-2-aldoxime for Co2; L3 = phenyl-2-pyridylketoxime for Co3) and picolinaldehyde O-methyl oxime (L4)-supported Co4 were synthesized and well characterized by FT-IR, mass spectrum and elemental analysis. The single-crystal X-ray diffraction of complex Co2 reveals that the cobalt center of CoCl2 is coordinated with two 6-methylpyridine-2-aldoxime ligands binding with Npyridine and Noxime atoms, which feature a distorted octahedral structure. These Co complexes Co1–Co4 displayed extremely high activity toward isoprene polymerization upon activation with small amount of AlClEt2 in toluene, giving polyisoprene with high activity up to 16.3 × 105 (mol of Co)−1(h)−1. And, the generated polyisoprene displayed high molecular weights and narrow molecular distribution with a cis-1,4-enriched selectivity. The type of cobalt complexes, cocatalyst and reaction temperature all have effects on the polymerization activity but not on the microstructure of polymer.
“…Moreover, the N oxime atoms of each ligand have a stronger coordination than N pyridine at the cobalt center according to the bond lengths [Co-N1 = 2.188 (17), Co-N2 = 2.098 (16), Co-N3 = 2.219 (16), Co-N4 = 2.132 (16)]. Consistent with the previous work of pyridine-oxime iron complex [65], the oxime proton is unionized. (15).…”
Section: Synthesis and Characterization Of Co(ii) Complexessupporting
confidence: 86%
“…2). However, it needs to be emphasized that the pyridine-oxime ligated iron complex bearing one 6-methyl substituent at pyridine ring showed lower activity because of steric hindrance in the previous work [65]. Zhang's group also reported that the substituent at the 6-position of the pyridine ring significantly influenced the catalytic performances of the iminopyridine ligated Co complexes.…”
Section: Polymerization Of Isoprene Catalyzed By Co(ii) Complexesmentioning
confidence: 94%
“…Ligands L1 and L3 were purchased and used directly without treatment. The ligands L2 and L4 were synthesized and characterized according to the previous report [65]. A typical procedure for the synthesis of ligand was carried out as follows.…”
Section: Co(ii) Complexes Preparationmentioning
confidence: 99%
“…Due to our ongoing burning desire to develop polymerization catalysts with high performance, we are interested in transition metal catalysts coordinating with N,N-bidentate ligands for diene polymerization [58][59][60][61][62][63][64]. In a recent piece of work, we reported that the pyridine-oxime ligand exhibited high performance in iron catalyzed isoprene polymerization with very low amount of methylaluminoxane [65]. Confirming the fundamental role played by the nature of the pyridine-oxime ligand and the type of cobalt catalyst in determining the catalytic activity and selectivity [66,67], herein we describe a series of pyridine-oxime ligated cobalt catalysts and study their catalytic properties for isoprene polymerization.…”
Several cobalt(II) complexes Co1–Co3 bearing pyridine–oxime ligands (L1 = pyridine-2-aldoxime for Co1; L2 = 6-methylpyridine-2-aldoxime for Co2; L3 = phenyl-2-pyridylketoxime for Co3) and picolinaldehyde O-methyl oxime (L4)-supported Co4 were synthesized and well characterized by FT-IR, mass spectrum and elemental analysis. The single-crystal X-ray diffraction of complex Co2 reveals that the cobalt center of CoCl2 is coordinated with two 6-methylpyridine-2-aldoxime ligands binding with Npyridine and Noxime atoms, which feature a distorted octahedral structure. These Co complexes Co1–Co4 displayed extremely high activity toward isoprene polymerization upon activation with small amount of AlClEt2 in toluene, giving polyisoprene with high activity up to 16.3 × 105 (mol of Co)−1(h)−1. And, the generated polyisoprene displayed high molecular weights and narrow molecular distribution with a cis-1,4-enriched selectivity. The type of cobalt complexes, cocatalyst and reaction temperature all have effects on the polymerization activity but not on the microstructure of polymer.
“…In 2018, Gong’s group demonstrated that cis -1,4- alt -3,4 polyisoprene can be achieved with aminophosphine(ory)-fused bipyridine-based cobalt complexes in combination with MMAO [ 3 ]. Subsequently, Wang and coworkers investigated the effect of fluorine substituents on isoprene polymerization catalyzed by iminopyridine-supported cobalt catalysts activated by AlEt 2 Cl or MAO/[Ph 3 C][B(C 6 F 5 ) 4 ] [ 32 , 33 , 34 ]. The binary system exhibited high catalytic activity and cis -1,4 selectivity, and also obtained high-molecular-weight polyisoprene.…”
A family of pyridine–oxazoline-ligated cobalt complexes L2CoCl2 3a–h were synthesized and characterized. Determined via single-crystal X-ray diffraction, complexes 3a and 3d, ligated by two ligands, displayed a distorted tetrahedral coordination of a cobalt center. The X-ray structure indicated the pyridine–oxazoline ligands acted as unusual mono-dentate ligands by coordinating only to Noxazoline. Upon activation with AlEt2Cl (diethylaluminum chloride), these cobalt complexes all exhibited high catalytic activity (up to 2.5 × 106 g·molCo−1·h−1), affording cis-1,4-co-3,4-polyisoprene with molecular weights of 4.4–176 kg mol−1 and a narrow Ð of 1.79–3.42, suggesting a single-site nature of the active sites. The structure of cobalt catalysts and reaction parameters, especially co-catalysts and the reaction temperature, all have significant influence on the polymerization activity but not on the microstructure of polyisoprene.
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