Monomeric and dimeric magnesium mono-BHT complexes as effective ROP catalysts

• Dimeric and monomeric 1:1 BHT-magnesium complexes have been synthesized.
• The first example of fully characterized (Aryloxide)Mg(Alkoxide) is reported.
• (BHT)Mg(Alkoxide) catalyses ROP of ε-CL, ω-PDL and (dl)-lactide.
• ROP initiated by (BHT)Mg(Alkoxide) goes by coordination-insertion mechanism.
• BHT-magnesium complexes catalyse heterotactic (dl)-lactide ROP with Pr up to 87%.

Monomeric and dimeric mono-BHT magnesium complexes [BuMg(μ-BHT)]2 (2), BuMg(BHT)(THF)2 (3), and [(μ-EtO)Mg(BHT)(THF)]2 (4) were synthesized starting from 2,6-di-tert-butyl-4-methylphenol (butylated hydroxytoluene, BHT-H) and Bu2Mg. The molecular structures of compounds 2–4 were established using X-ray diffraction. Being activated by alcohol (monomeric 3) or thermally (dimeric 4), mono-BHT complexes demonstrate high catalytic activity in the ring-opening polymerization of ε-caprolactone (ε-CL), ω-pentadecalactone (ω-PDL) and (dl)-lactide. In the latter case, a heterotactic polymer with a Pr of up to 87% is formed. Analysis of the terminal groups of poly(ε-CL), which was obtained using 3/BnOH, indicated that the ROP initiator possesses an alkoxy-magnesium nature.

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