Rare‐earth metal derivatives supported by aminophenoxy ligand: Synthesis, characterization and catalytic performance in lactide polymerization

Abstract

A library of rare‐earth metal derivatives supported by an aminophenoxy ligand was prepared and their catalytic performance in lactide polymerization was investigated. It was found that the synthetic strategy had a profound effect on the formation of aminophenoxy rare‐earth metal complexes. Amine elimination between Ln[N(SiMe3)2]3(μ‐Cl)Li(THF)3 (Ln = Yb, Y) and 1 equiv. of the aminophenol [HONH] ([HONH] = ο‐OCH3‐C6H4NHCH2(3,5‐tBu2‐C6H2‐2‐OH)) in toluene gave the unexpected heterobimetallic bis(aminophenoxy) rare‐earth metal complexes [ON]2LnLi(THF)2 (Ln = Yb (1), Y (2)). When the reactions were carried out in THF and TMEDA, amine elimination produced the aminophenoxy rare‐earth metal amide complexes {[ON]LnN(SiMe3)2}2 (Ln = Yb (5), Y (6)) in ca 85% isolated yields. Complexes 5 and 6 could also be obtained from salt metathesis reaction of {[ON]LnCl(THF)}2 (Ln = Yb (3), Y (4)) with NaN(SiMe3)2 in a 1:2 molar ratio. In addition, treatment of complexes 3 and 4 with NaOAr (Ar = &bond;C6H4‐4‐tBu) and (SiMe3)2NC(NPri)2Na in 1:4 and 1:2 molar ratios provided the corresponding aminophenoxy rare‐earth metal derivatives {[ON](μ‐OAr)Ln(μ‐OAr)Na(THF)2}2 (Ln = Yb (7), Y (8)) and {[ON]Ln[(iPrN)2CN(SiMe3)2]}2 (Ln = Yb (9), Y (10)), respectively. These complexes were fully characterized, and their molecular structures were determined using single‐crystal X‐ray diffraction. Polymerization experiments showed that complexes 1, 2, 5, 6, 9 and 10 were highly active for the ring‐opening polymerization of l‐lactide in toluene, and complex 1 promoted l‐lactide polymerization in a controlled fashion. The polymerization of rac‐lactide initiated by the neutral aminophenoxy rare‐earth metal complexes 5, 6, 9 and 10 in THF afforded heterotactic polymers.

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

“…The latter is very important for catalysis applications [ 13 ]. 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.…”