Controlled isoprene polymerization mediated by iminopyridine-iron (II) acetylacetonate pre-catalysts

A ligand controlled stereoselective polymerization of isoprene has been developed. A series of (aryl/alkyl)-iminopyridine iron (II) acetylacetonate complexes: (aryl = Ph Fe1; alkyl = CH2Ph Fe2, CH (Ph)(2) Fe3, CH (Me)(2) Fe4, C (Me)(3) Fe5, C (Me)(2)CH2 C(Me)(3) Fe6), has been prepared in which steric and electronic substituents systematically modified to investigate their influences for isoprene polymerization. The molecular structure of representative complex Fe2 was confirmed by single crystal X-ray diffraction and, revealed a distorted octahedral geometry at iron center. On treatment with methylaluminoxane (MAO), Fe1-Fe6 displayed low (Fe5 & Fe6) to high activities (Fe1-Fe4) with quantitative monomer conversion (>99%) for isoprene polymerization producing polyisoprene of high molecular weight (up to 2.0 x 10(5) g/mol) and unimodal molecular weight distribution (1.4-3.3). Specifically, complex Fe2 (alkyl = CH2Ph) displayed the highest activity of 7.0 x 10(6) g (mol of Fe)(-1) h(-1) with 85% conversion of monomer over run time of 10 min at 25 degrees C. While, Fe6 catalyzed polyisoprene possessed high content of trans-1,4 unit (up to 87%). Furthermore, the influence of the reaction parameters and the nature of the ligands on the catalytic activities and microstructural properties of the polymer were investigated in detail.