Zinc bimetallics supported by a xanthene-bridged dinucleating ligand: synthesis, characterization, and lactide polymerization studies

Abstract

Di-zinc complexes of a new dinucleating xanthene-based bis(iminophenolate) ligand have been synthesized, and their coordination chemistry and lactide polymerization activity have been investigated.

Dinucleating Amino-Phenolate Platform for Zinc Catalysts: Impact on Lactide Polymerization

“…The polymerization of 600 equiv of rac-LA using imine alkoxy zinc complex 4 (Table 2, entry 8) reached 89% in 24 h, with a Đ of 1.26 exhibiting comparable activity to the xanthene-bridged dinuclear zinc catalyst reported by Groysman and coworkers. 94 The 1 H{ 1 H} NMR spectra of PLA produced from rac-LA with complexes 3 and 4 yielded a heterotactic enriched PLA with P r values of 0.61 and 0.67 (Figures S54, S55), respectively, while with complex C (Chart 1) an atactic PLA was generated.…”

Zinc Complexes Bearing Dinucleating Bis(imino‐ pyridine)binaphthol Ligands: Highly Active and Robust Catalysts for the Lactide Polymerization

“…On the other hand, tailored dinucleating ligands have been designed in order to assure the spatial proximity of two zinc centers, a fundamental requirement for their cooperativity. Among the related complexes, active catalysts in the synthesis of PLA are bis(diamino)‐ and bis(diimino)‐phenolate dinuclear zinc complexes reported by Tolman and Williams [10] and subsequently by Mehrkhodavandi, [11] various dizinc complexes bearing NNO‐scorpionate ligands explored by Otero, [12] in addition to xanthene‐bridged bis(iminophenolate), [13] calixarene, [14] bis(salalen) [15] and bis(iminopyrrolide) [16] dizinc complexes. To date, the most active catalyst for the ring‐opening polymerization of lactide in solution is a bis(imino)diphenylamido dizinc complex, reported in 2016 by Williams and Brooker, [17] which showed TOF up to 60000 h −1 and worked efficiently also under immortal conditions or at very low catalyst loading.…”

Cooperative effects of Schiff base binuclear zinc complexes on the synthesis of aliphatic and semi-aromatic polyesters

“…In addition, TBAB and DMAP gave the most selective catalytic systems; in fact, in both cases, copolymerization proceeded in an exclusive alternating fashion with an ester content linkage of >99%. Thus, we selected TBAB as the co-catalyst to compare the behavior of complexes 1-3 in this class of copolymerization reactions under the same reaction conditions (entries [22][23][24]. By comparing the conversions after 16 hours of polymerization reaction, the three complexes showed the following order of activity: 1 > 2 > 3, which is the same as that of ε-caprolactone polymerization.…”

“…Noteworthily, binuclear zinc complexes often show higher activity or peculiar catalytic behaviors compared to their monometallic counterparts, thanks to the synergistic interactions between zinc atoms. 17–19 The most relevant examples of di-zinc complexes reported in the literature are supported by phenoxy-based ancillary ligands both for the ROP of lactide 20–30 and ε-caprolactone 31–35 and for the ROCOP of epoxides and cyclic anhydrides. 35–39…”

“…Noteworthily, binuclear zinc complexes often show higher activity or peculiar catalytic behaviors compared to their monometallic counterparts, thanks to the synergistic interactions between zinc atoms. [17][18][19] The most relevant examples of dizinc complexes reported in the literature are supported by phenoxy-based ancillary ligands both for the ROP of lactide [20][21][22][23][24][25][26][27][28][29][30] and ε-caprolactone [31][32][33][34][35] and for the ROCOP of epoxides and cyclic anhydrides. [35][36][37][38][39] As part of our research interest in zinc complexes in the ROP of cyclic esters, [40][41][42][43][44] we recently reported di-nuclear zinc complexes supported by properly designed bis(imino-pyridine) binaphthol ligands.…”