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A series of magnesium silylamido complexes supported by tetradentate aminophenolate ligands, LMgN(SiMe 3 ) 2 (L = {(2-R 1 )Ar-CH 2 N[(CH 2 ) 2 R 2 ]CH 2 -(4-R 4 -6-R 3 )C 6 H 2 O − }, R 1 = NMe 2 , R 2 = N i Pr 2 , R 3 = R 4 = Cl ( 1 ), R 3 = R 4 = cumyl ( 2 ); R 1 = NMe 2 , R 2 = NEt 2 , R 3 = R 4 = cumyl ( 3 ), R 3 = CPh 3 , R 4 = Me ( 4 ); R 1 = NEt 2 , R 2 = NEt 2 , R 3 = CPh 3 , R 4 = Me ( 5 ); R 1 = NMe 2 , R 2 = ( S )-1-butylpyrrolidine-2-yl, R 3 = R 4 = cumyl ( 6 ), R 3 = CPh 3 , R 4 = Me ( 7 )), were synthesized and fully characterized, and their catalytic behaviors for the ring-opening polymerization (ROP) of rac -lactide ( rac -LA) were explored. The monomeric nature and versatile coordination modes of these complexes in the solid state were further confirmed by X-ray diffraction studies on complexes 1 , 3 and 7 . In complex 1 , the N , N -diisopropylamino group on the alkylamino side arm does not coordinate to the metal centre, whilst the remaining three donors of the aminophenolate ligand and the silylamido group bond with the magnesium centre. By contrast, in complexes 3 and 7 , the arylamino moiety does not coordinate to the metal centre, while the alkylamino side arm coordinates. It is worth noting that the introduction of the N , N -dimethyl amino group to the pendant benzyl group realises the diastereoselective synthesis of multichiral aminophenolate magnesium complexes, which has not been achieved by the corresponding tridentate aminophenolate ligand. It was found that most of these magnesium complexes serve as highly active initiators for the ROP of rac -LA. The coordination pattern of the aminophenolate ligand exerted a considerable influence on the activity and stereoselectivity of the corresponding complex toward the polymerization of rac -LA, leading to the production of moderate to high heterotactic biased PLAs. The enantiopure complex 7 showed the highest heteroselectivity among these magnesium complexes ( P r = 0.80 in toluene, P r = 0.82 in THF). [ABSTRACT FROM AUTHOR]

Mono(ketiminate) aluminum dimethyl complexes 1a – 5a and bis(ketiminate) aluminum methyl complex 2b were synthesized via the reactions of AlMe 3 with various N -aryl substituted ketimine compounds in a 1:1 or 1:2 molar ratio, respectively. The reaction of Al(O i Pr) 3 with the ketimine compound L 2 H resulted in a bis(ketiminate) aluminum isopropoxide complex 2c . All the complexes were characterized by 1 H and 13 C{ 1 H} NMR spectroscopy, either EA or HRMS analysis. X-ray diffraction measurement of complexes 2a and 3a confirmed that in the solid state both 2a and 3a exist as a tetrahedron structure with the aluminum atom center surrounded by the oxygen and nitrogen donors of the bis-chelating ketiminate ligand as well as two methyl groups. Besides, a triligated aluminum complex 3 (Al(L 3 ) 3 ) with a six-coordinated metal core and a dinuclear aluminum isopropoxide complex 6d [(L 6 ) 2 Al(μ-O i Pr) 2 Al(O i Pr) 2 ] with C 2 -symmetry were isolated and characterized by X-ray diffraction studies. All aluminum methyl complexes behaved as active initiators in the ring-opening polymerization (ROP) of rac- lactide ( rac -LA), affording isotactic-enriched polylactides (PLAs) with high molecular weights and broad molecular weight distributions at 70 °C. The steric and electronic characters of the ancillary ligands show significant effects both on the activity and the stereoselectivity. The introduction of an electron-withdrawing group on the para -position of N -aryl ring of the ligand resulted in an increase of the catalytic activity. However, the electronic character of ancillary ligands showed a neglectable effect on the ROP of ε -CL initiated by these aluminum complexes. For both monomers, bis(ketiminate) aluminum complex 2b was found to be more active than the corresponding mono(ketiminate) complex 2a of the same ligand. Aluminum isopropoxide complex 2c exerted better control for the polymerizations of both monomers, providing polymers with narrower molecular weight distributions and smaller molecular weights which are comparable to the theoretical values [ABSTRACT FROM AUTHOR]