Synthesis, structures, and catalytic activity toward the ring-opening polymerization of ε-caprolactone of zinc complexes supported by β-diketiminate ligands with a large aryl group

Seven zinc complexes based on a series of beta-diketiminate ligands are reported. Reactions of ZnEt2 with HL1-HL5 (HL1 = N-(4-((4-chlorophenyl)imino)pent-2-en-2-yl)-2,4,6-tricyclopentylaniline, HL 2 = 2,4,6-tricyclopentyl-N-(4-((2-methoxyphenyl)imino)pent-2-en-2-yl)aniline, HL 3 = 2,4,6-tricyclopentyl-N-(4-((4nitrophenyl)imino)pent-2-en-2-yl)aniline, HL4 = 2,4,6-tricyclopentyl-N-(4-(mesitylimino)pent-2-en-2yl)aniline, HL5 = 2,4,6-tricyclopentyl-N-(4-(pyridin-2-ylimino)pent-2-en-2-yl)aniline) afforded compounds [Zn(L-1 )Et] (1 ), [Zn(L-2 )Et] (2 ), [Zn(L-3 )Et] (3 ), [Zn(L-4)Et] (4)and [Zn(L-5)Et]2 (5)in high yields. Complexes [Zn(L-1)I(THF)] (6)and [Zn(L-2)I(THF)] (7)were obtained by the reactions of 1 and 2 , respectively, with one equivalent of I-2. The structures of 1-7 were determined by single crystal X-ray diffraction analysis. The catalytic behavior of 1-7 for the ring-opening polymerization (ROP) of epsilon-caprolactone (epsilon-CL) was explored. Compounds 1-4 were all active for the ROP reactions. The polymers obtained by using complex 2 as an initiator showed a large molecular weight and narrow molecular weight distribution. The structures of the obtained polymers were characterized by MALDI-TOF-MS, IR and H-1 NMR spectroscopy. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

In this study, seven zinc complexes based on beta-diketiminate ligands were reported, and their catalytic behavior in the ring-opening polymerization of epsilon-caprolactone was investigated. Some of the complexes exhibited high activity and resulted in polymers with high molecular weight and narrow molecular weight distribution.