Mn(II) and Fe(II) complexes of bidentate Schiff Base as mediators for Organometallic Mediate Radical Polymerization (OMRP) of Vinyl Acetate

In the last decades, controlled radical polymerization (CRP) has become very important, since it facilitates the synthesis of macromolecules of specific architectures with excellent control over the chemical and physical properties. Here, this study describes the synthesis and characterization of a series of novel manganese(II) and iron(II) complexes of Schiff base derived from the salicylaldehyde and different cycloalkylamines (cycloalkyl = cyclopentyl-1a, cyclohexyl-1b, cycloheptyl-1c, and cyclooctyl-1d) (Scheme 1). The MnII and FeII complexes of Schiff base were prepared in good yields from the metallation of the corresponding ligands 1a-1d with MnCl2 and FeCl2, respectively, by stirring and heating under reflux. The complexes were characterized by elemental analyses, FTIR, UV-vis, electron paramagnetic resonance spectroscopy, cyclic voltammetry, and computational methods. The MnII and FeII complexes were applied as controlling agents for the polymerization of vinyl acetate (VAc) initiated by AIBN, according to an organometallic-mediated radical polymerization (OMRP) mechanism. The influences of the Schiff base ligand structure, focusing the steric hindrance at the manganese and iron center, were assessed by modification of the cycloalkyl substituents. Different conditions of reaction time, concentrations of VAc and AIBN as initiator were investigated. The VAc polymerization mediated by theses complexes suggests that the level of control can be slightly tuned by the substitution of the cycloalkyl group on the Schiff base ligand and the metal center.