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Abstract :
[en] Organocobalt(III) with acetylacetonate ligands is the most representative example of R-Co bearing a weak C-Co bond that can release alkyl radicals under mild experimental conditions without requiring a photoactivation. The unique isolated specimen is a short oligo(vinyl acetate) end-capped by Co(acac)2. The high lability of the C-Co bond of this R-Co combined to the unique capacity of Co(acac)2 to reversibly trap alkyl radicals make this organocobalt unique for the precision synthesis of unprecedented polymers by the so-called Cobalt-Mediated Radical Polymerization (CMRP) technique. The growth of unstabilized and highly reactive growing radicals formed by the addition of R· to unconjugated olefins (vinyl esters, vinyl amides, vinyl imidazolium, vinyl chloride, ethylene) is controlled by the reversible formation of a weak C-Co bond at the polymer chain end. The lack of alternatives to this R-Co, especially to the structure of the alkyl group, has placed limitations on further innovation in (macro)molecular design. Other functional variants that would enable attractive chain-end derivatizations are unfortunately not available.
In this communication, we will address this important challenge by describing an innovative synthetic route towards the preparation of a new functional R-Co(acac)2 that are characterized by a weak C-Co bond. We will report the conditions required for initiating and controlling the radical polymerization of various monomers from these R-Co. We will also demonstrate their utility for the production of novel telechelic polymers under mild experimental conditions, syntheses that can be carried out in water.