Aminephenolates of aluminum, gallium and zinc: synthesis, characterization and polymerization activity

Complexes containing aminophenolate ligands are considered as very efficient initiators of ring-opening polymerization (ROP). Our systematic studies of the reactions of two selected aminophenols, 2-[(p-tolylamino)methyl]-4-(2,4,4-trimethylpentan-2-yl)phenol (L'H2) and 2-cyclohexylaminomethyl-4-methylphenol (L"H2), with alkyl compounds of aluminium, gallium and zinc resulted in the formation of a variety of products depending on the type of metallic centre and alkyl groups bonded to metal atoms. Vew trinuclear aluminium complexes (Me5Al3(L')2 (1) and Me5Al3(L")2 (2)), monomeric aluminium (tBuAl(L'H) (3) and tBu2Al(L"H) (5)) and gallium (tBu2Ga(L'H) (4) and tBu2Ga(L"H) (6)) compounds, and dinuclear gallium (Et2Ga(L"H).Et3Ga (7)) and zinc (tBuZn(L"H)]2 (8)) complexes were isolated and characterized. The molecular and crystal structures of 7 and 8 were determined on the basis if an X-ray diffraction study. Polymerization tests showed that only three complexes (6-8) had activity in the ROP of e-caprolactone, whereas 1-5 were inactive in ROP.