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

Iron complexes of the types [Fe(HL)Cl] (: HL = pyridine-2-aldoxime; : HL = 6-methylpyridine-2-aldoxime; : HL = phenyl-2-pyridylketoxime; : HL = picolinaldehyde O-methyl oxime) were prepared and characterized by elemental analysis and IR spectroscopy. The crystal structure of , determined by single-crystal X-ray diffraction, featured a distorted octahedral coordination of the iron center binding with two ligands of HL. The X-ray structure and infrared spectral data indicated that pyridine-oxime ligands act as unionized bidentate ligand by coordinating with N and N. 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 , and were found to be highly active (up to 6.5 × 10 g/mol·h) in -1,4--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 [PhC][B(CF)]/AlR for the ternary catalytic system, theses complexes showed extremely high activities, as well about 98% yield after 2 min, to afford -1,4--3,4-polyisoprene with a molecular weight of 140-420 kg/mol.