Synthesis, Characterization and Catalytic Property Studies for Isoprene Polymerization of Iron Complexes Bearing Unionized Pyridine-Oxime Ligands.

Iron complexes of the types [Fe(HL) 2 Cl 2 ] ( Fe1 : HL 1 = pyridine-2-aldoxime; Fe2 : HL 2 = 6-methylpyridine-2-aldoxime; Fe3 : HL 3 = phenyl-2-pyridylketoxime; Fe4 : HL 4 = 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 HL 2 . The X-ray structure and infrared spectral data indicated that pyridine-oxime ligands act as unionized bidentate ligand by coordinating with N pyridine and N oxime . The catalytic performance for isoprene polymerization, catalyzed by these pyridine-oxime-ligated iron complexes, was examined. For a binary catalytic system combined with MAO, complexes Fe1 , Fe3 and Fe4 were found to be highly active (up to 6.5 × 10 6 g/mol·h) in cis -1,4- alt -3,4 enchained polymerization, with average molecular weights in the range of 60-653 kg/mol and narrow PDI values of 1.7-3.5, even with very low amounts of MAO (Al/Fe = 5). Upon activation with [Ph 3 C][B(C 6 F 5 ) 4 ]/AlR 3 for the ternary catalytic system, theses complexes showed extremely high activities, as well about 98% yield after 2 min, to afford cis -1,4- alt -3,4-polyisoprene with a molecular weight of 140-420 kg/mol.