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

In this work, alkali metal-magnesium aryloxides [Mg2Li2(MesalO)(6)] (1), [Mg2Na2(MesalO)(6)(THF)(x)] for x = 2 or 4 (2), and [Mg2K2(MesalO)(6)(THF)(4)] (3) derived from the reaction of (MgBu2)-Bu-n and nBuLi, metallic Na or K with methyl salicylate (MesalOH) were used as molecular platforms for the synthesis of new heterometallic compounds [Mg2Li2(EtsalO)(6)] (4), [MgK(EtsalO)(3)]n (5), [Mg6Na4Al(MesalO)(13)(OH)(6)(MesalOH)(THF)(0.5)(H2O)(0.5)] (6), and [Mg4Na2(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 (MgBu2)-Bu-n stabilized with 1 wt% AlEt3 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 (MgBu2)-Bu-n 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.