Organometallic-mediated radical polymerization using well-defined Schiff base cobalt(II) complexes

Abstract

A series of new cobalt(II) complexes of Schiff base derived from salicylaldehyde and different cycloalkylamines (cycloalkyl = cyclopentyl-1a, cyclohexyl-1b, and cycloheptyl-1c) was synthesized: [Co(CyPen-Salicyl) 2 ] (2a), [Co(CyHex-Salicyl) 2 ] (2b), and [Co(CyHep-Salicyl) 2 ] (2c). The bis(phenoxyiminato)Co(II) complexes (2a-2c) have been fully characterized by FTIR and UV–vis spectroscopy, elemental analysis, cyclic voltammetry, computational methods, and two of the complexes were further studied by single crystal X-ray crystallography. The X-ray structure analysis of 2a-b shows that the geometry around the metal atom is a distorted tetrahedron, confirming the spectroscopic data. Electrochemical studies suggest that the redox potential of 2a-2c are sensitive to the substituent group, decreasing in order cyclopentyl > cyclohexyl > cycloheptyl. Complexes 2a-2c were used as controlling agents for the polymerization of vinyl acetate (VAc) initiated by AIBN, according to a cobalt-mediated radical polymerization (CMRP) mechanism. The VAc polymerization mediated by 2a-2c suggests that the level of control can be slightly tuned by the substitution of the cycloalkyl group on the Schiff base ligand. Complex 2b showed the smaller discrepancy between observed and calculated molecular weight, and narrower molecular weight distribution.