Synthesis, Characterization, and Catalytic Studies of (Aryloxido)magnesium Complexes

The reaction of MgBu2 with 1 equiv. of four‐coordinating (R)‐ or rac‐N,N‐bis(3,5‐di‐tert‐butylbenzyl‐2‐hydroxy)tetrahydrofurfurylamine (R/rac‐bpthfa‐H2) gave dinuclear homoleptic [Mg(μ‐R/rac‐bpthfa)]2 (R/rac‐2c) as white powders in54–67 % yields. Analogous reactions of MgBu2 with 2 equiv. of two‐coordinating N‐(3,5‐di‐tert‐butylbenzyl‐2‐hydroxy)‐N‐methylcyclohexanamine (tbpca‐H; 1e‐H) and (S)‐N‐(3,5‐di‐tert‐butylbenzyl‐2‐hydroxy)‐N,α‐dimethylbenzylamine(S‐tbpmpa‐H; S‐1f‐H) gave white crystals of homoleptic mononuclear compounds of general formula [Mg(L)2] (2e and S‐2f) in 87–89 % yields. The resulting aminophenolates were characterized by spectroscopic methods and, in the case of R‐2c and S‐2f, by X‐ray crystallography. The new complexes R/rac‐2c, 2e, and S‐2f, as well as the previously described homo‐ and heteroleptic tetranuclear [Mg(ddbfo)2]4 (2a), [Mg(thffo)2]4 (2b), [Mg4(μ3‐OMe)2(μ,η2‐ddbfo)2(μ,η1‐ddbfo)2(η1‐ddbfo)2(MeOH)5]·CH3OH·thf (3a·CH3OH·thf) and [Mg4(μ3,η2‐thffo)2(μ,η2‐thffo)2(Ph3SiO)2] (4b), were tested in the polymerization of lactide to reveal good activity only in the case of mononuclear four‐coordinate species grafted with an external donor, benzyl alcohol.