Use of heterometallic alkali metal-magnesium aryloxides in ring-opening polymerization of cyclic esters.

In this work, alkali metal-magnesium aryloxides [Mg 2 Li 2 (MesalO) 6 ] (1), [Mg 2 Na 2 (MesalO) 6 (THF) x ] for x = 2 or 4 (2), and [Mg 2 K 2 (MesalO) 6 (THF) 4 ] (3) derived from the reaction of Mg n Bu 2 and n BuLi, metallic Na or K with methyl salicylate (MesalOH) were used as molecular platforms for the synthesis of new heterometallic compounds [Mg 2 Li 2 (EtsalO) 6 ] (4), [MgK(EtsalO) 3 ] n (5), [Mg 6 Na 4 Al(MesalO) 13 (OH) 6 (MesalOH)(THF) 0.5 (H 2 O) 0.5 ] (6), and [Mg 4 Na 2 (MesalO) 6 (SalO) 2 (THF) 4 ] (7) (EtsalOH = ethyl salicylate and SalOH 2 = salicylic acid) by the reaction with EtOH, exposure to atmospheric moisture or addition of stoichiometric quantities of water. Compounds 4 and 5 were synthesized by transesterification of 1 and 3. Cluster 6 was formed haphazardly by exposing a THF solution of 2 derived using Mg n Bu 2 stabilized with 1 wt% AlEt 3 to atmospheric moisture. Compound 7 was synthesized by partial hydrolysis of 2. Homometallic magnesium aryloxide [Mg 4 (MesalO) 4 (OMe) 4 (HOMe) 4 ] (8) was obtained by reaction of Mg n Bu 2 and MesalOH in a methanol solution. The catalytic activity of 1-3 and 6-8 was investigated in the ring-opening polymerization (ROP) of L-lactide (L-LA) or benzaldehyde Tishchenko reaction.