Aminophenolates of aluminium, gallium and zinc: Synthesis, characterization and polymerization activity

Abstract

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. New trinuclear aluminium complexes (Me5Al3(L′)2 (1) and Me5Al3(L″)2 (2)), monomeric aluminium (tBu2Al(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 of an X‐ray diffraction study. Polymerization tests showed that only three complexes (6–8) had activity in the ROP of ε‐caprolactone, whereas 1–5 were inactive in ROP.

Gallium (III) Complexes Based on Aminobisphenolate Ligands: Extremely High Active ROP-Initiators from Well-Known and Easily Accessible Compounds

“…Aminobisphenolate complexes of main group elements (for example, Al [ 14 , 15 , 16 , 17 , 18 , 19 ], alkali metals [ 20 , 21 , 22 ], Ca [ 21 ], Mg [ 23 ]), transition metals (for example, Ti [ 19 ]) and lanthanides [ 24 , 25 ] have been reported to catalyze ROP reactions, but by now there is absolutely no information not only about catalysis but also about the synthesis of such gallium complexes in general. At the same time, gallium is a non-toxic metal if one may consider the concentrations of metal compounds that remain in the polymer during its synthesis [ 26 ], in addition, there are examples of the use of some gallium complexes in medicine [ 27 ], and gallium complexes of various structures (for example, diamido-ether dianionic ligands, (aminomethyl)phenolate monoanionic ligands, 8-quinolinolato monoanionic ligands, salan dianionic ligands, salen dianionic ligands, bis(imino)phenoxide monoanionic ligands) are active in ROP as initiators, [ 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 ] thus aminobisphenolate gallium derivatives should be considered as potentially promising ROP initiators and interesting targets for their synthesis and investigation of their behavior in ROP.…”

Highly active tridentate amino-phenol zinc complexes for the catalytic ring-opening polymerization of ε-caprolactone

“…Numerous metal complexes have been used to initiate the ROP of cyclic esters [4,5], mostly containing e.g. alkali metals [6e10], alkaline earth metals [11e15], Group IVB metals [16e21], rare earth metals [22e27], aluminum [28e34], copper [35,36], gallium [37,38]. However, traces of residual metal in the polymers formed are very hard to be completely removed, which is harmful to the environment or humans and consequently limits their applications of polymers.…”