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International audience; The synthesis and characterization of cobalt(II) (3, 4) and acetato cobalt(III) (5) complexes with two tripodal tetradentate diamino-bis(phenolate) ligands (L1 and L2) are reported. The solid-state structures of proligand H2L1 and complexes 4 and 5 were determined by X-ray crystallography. Complex 4 crystallizes as a dimer via the formation of a Co2O2 core. Complex 5 is monomeric with a six-coordinated cobalt(III) center bearing a chelating acetate ligand. In both structures, the diamino-bis(phenolate) ligand (L1 or L2) is acting as a tetradentate dianionic κ4-(O2,N2) chelating ligand. The diamagnetic nature of complex 5 allowed its characterization by multinuclear NMR spectroscopic techniques. Complex 5 is not a competent unimolecular initiator for the radical polymerization of methyl acrylate or methyl methacrylate. Its cobalt(II) analog (3) did not act as an efficient OMRP moderator for the radical polymerization of activated (styrene, tert-butyl acrylate) and non-activated (vinyl acetate) monomers.

International audience; The addition of benzoyl peroxide to [CoII(acac)2] in a 1:2 ratio selectively produces [CoIII(acac)2(O2CPh)], a diamagnetic (NMR) mononuclear CoIII complex with an octahedral (X-ray diffraction) coordination geometry. It is the first reported mononuclear CoIII derivative with a chelated monocarboxylate ligand and an entirely O-based coordination sphere. The compound degrades in solution quite slowly by homolytic CoIII-O2CPh bond cleavage upon warming above 40°C to produce benzoate radicals and can serve as a unimolecular thermal initiator for the well-controlled radical polymerisation of vinyl acetate. Addition of ligands (L = py, NEt3) induces benzoate chelate ring opening and formation of both cis and trans isomers of [CoIII(acac)2(O2CPh)(L)] for L = py under kinetic control, then converting quantitatively to the cis isomer, whereas the reaction is less selective and equilibrated for L = NEt3. The py addition strengthens the CoIII-O2CPh bond and lowers the initiator efficiency in radical polymerisation, whereas the NEt3 addition results in benzoate radical quenching by a redox process. In addition to clarifying the mechanism of the radical polymerisation redox initiation by peroxides and rationalizing the quite low efficiency factor for the previously reported [CoIIacac)2]/peroxide-initiated organometallic-mediated radical polymerisation (OMRP) of vinyl acetate, this investigation provides relevant information on the CoIII-O homolytic bond cleavage process.

Magnetic biopolymer hybrid nanoparticles have gained a lot of attention in the field of biomedical applications. Here we present the synthesis of hyaluronic acid (HA)-coated magnetic clusters of superparamagnetic nanoparticles. Firstly, the superparamagnetic magnetite nanoparticles coated with oleic acid were synthesized and characterized in terms of size, composition and magnetic properties. Secondly, magnetic nanoclusters were prepared and wrapped with HA grafted with an ethylene glycol-based copolymer. The resulting nanostructures and nanobeads were characterized using electron microscopy, dynamic light scattering, thermogravimetric analysis and magnetic measurements. The clustering of magnetite nanoparticles facilitates magnetic purification, separation, rapid attraction and controlled positioning by high field gradient micro-magnet arrays. In addition, clusters could be formed in the presence of a fluorescent drug model, which demonstrates the possibility of dual functionalization of our hybrid nanosystems: magnetic responsiveness and drug encapsulation.