Simple magnesium alkoxides: synthesis, molecular structure, and catalytic behaviour in the ring-opening polymerization of lactide and macrolactones and in the copolymerization of maleic anhydride and propylene oxide.

The synthesis of two chiral bulky alkoxide pro-ligands, 1-adamantyl- tert -butylphenylmethanol HOCAd t BuPh and 1-adamantylmethylphenylmethanol HOCAdMePh, is reported and their coordination chemistry with magnesium(II) is described and compared with the coordination chemistry of the previously reported achiral bulky alkoxide pro-ligand HOC t Bu 2 Ph. Treatment of n -butyl- sec -butylmagnesium with two equivalents of the racemic mixture of HOCAd t BuPh led selectively to the formation of the mononuclear bis(alkoxide) complex Mg(OCAd t BuPh) 2 (THF) 2 . 1 H NMR spectroscopy and X-ray crystallography suggested the selective formation of the C 2 -symmetric homochiral diastereomer Mg(OC R Ad t BuPh) 2 (THF) 2 /Mg(OC S Ad t BuPh) 2 (THF) 2 . In contrast, the less sterically encumbered HOCAdMePh led to the formation of dinuclear products indicating only partial alkyl group substitution. The mononuclear Mg(OCAd t BuPh) 2 (THF) 2 complex was tested as a catalyst in different reactions for the synthesis of polyesters. In the ROP of lactide, Mg(OCAd t BuPh) 2 (THF) 2 demonstrated very high activity, higher than that shown by Mg(OC t Bu 2 Ph) 2 (THF) 2 , although with moderate control degrees. Both Mg(OCAd t BuPh) 2 (THF) 2 and Mg(OC t Bu 2 Ph) 2 (THF) 2 were found to be very effective in the polymerization of macrolactones such as ω-pentadecalactone (PDL) and ω-6-hexadecenlactone (HDL) also under mild reaction conditions that are generally prohibitive for these substrates. The same catalysts demonstrated efficient ring-opening copolymerization (ROCOP) of propylene oxide (PO) and maleic anhydride (MA) to produce poly(propylene maleate).