Synthesis of cobalt(II)-α-diimines complexes and their activity as mediators in organometallic mediated radical polymerization of vinyl acetate

• Published in: Inorganica Chimica Acta 2018-02, Vol.471, p.620-629
• Main Authors: Riga, Beatriz A., Neves, Marina D., Machado, Antonio E.H., Araújo, Diesley M.S., Souza, Jhonathan R., Nascimento, Otaciro R., Santana, Vinícius T., Cavalheiro, Carla C.S., Carvalho-Jr, Valdemiro P., Goi, Beatriz E.
• Format: Article
• Language: English
• Subjects: CMRP; Radical polymerization; Vinyl acetate; α-Diimine-cobalt complexes
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/j.ica.2017.11.041

The synthesis and characterization of three Co(II) complexes bearing α-diimine ligands and their application as mediating agents for vinyl acetate controlled radical polymerization. The overall results of this study suggest that steric effects in the ligand play a significant role in determining organometallic reactivity trends and catalytic properties. [Display omitted] •Cobalt(II)-α-diimine complexes were successfully synthesized and characterised.•Cobalt(II)-α-diimine complexes were applied in CMRP of vinyl acetate.•The CMRP was dependent on the [initiator]/[monomer]/[Co], and reaction time.•α-diimine as ancillary ligands can tune the reactivity of mediators in CMRP. This study describes the synthesis and characterization of three α-diimine-cobalt complexes of the type [CoCl2(R-DAB)] (R-DAB = RNCHCHNR; R = Mes, Dipp and Dipp∗) and their application as mediators for the cobalt-mediated radical polymerization (CMRP) of vinyl acetate (VAc) using 2,2′-Azobis(2-methylpropionitrile) (AIBN) as initiator. The complexes were characterised by elemental analyses, FTIR, UV–Vis, electron paramagnetic resonance spectroscopy, cyclic voltammetry, and computational methods. The systematic variation of the reaction conditions, such as [initiator]/[Co] and [monomer]/[Co] molar ratios at 65 °C, affected the polymerization rates and the molecular weights, reaching a certain level of control. The VAc polymerization was initiated by AIBN in the presence of DMSO using the α-diimine-cobalt complexes as mediators with [DMSO]/[Co] = 1 at 65 °C. The control over the polymer produced was not improved after the addition of DMSO. Kinetics studies and computational investigations support a tailorable cobalt complex reactivity mainly altered by steric factors of the α-diimine ligands.