Inside Back Cover: Dinuclear Zinc–N‐Heterocyclic Carbene Complexes for Either the Controlled Ring‐Opening Polymerization of Lactide or the Controlled Degradation of Polylactide Under Mild Conditions (ChemCatChem 5/2014)

Abstract

Multipurpose zinc carbene catalystThe cover picture features a dinuclear zinc-N-heterocyclic carbene (NHC) catalyst. In their Full Paper on p. 1357 ff., S. Dagorne, T. AvilØs, M. J. Calhorda et al. report that such zinc-NHC alkoxide species polymerize lactide to produce well-defined polylactic acid and, remarkably, also mediate the controlled degradation (depolymerization) of polylactic acid under mild conditions to produce methyl lactate as the major reaction product. DFT studies of the polymerization reaction highlight the beneficial effect of two zinc centers in close proximity. The work shows that biocompatible zinc(II) complexes can mediate the polymerization of lactide and the controlled degradation of polylactic acid under mild conditions (room temperature).

Coordination Ring-Opening Polymerization of Cyclic Esters: A Critical Overview of DFT Modeling and Visualization of the Reaction Mechanisms

“…A similar pattern (reaction mechanism without the formation of highly stable chelates) was detected by Dagorne et al who studied l- LA ROP, catalyzed by dimeric NHC zinc complex 64 (Figure 32) [147]. DFT calculations were performed at the PBE0 [142] level of theory using Stuttgart effective core potentials and their associated basis set [107] for zinc and the 6-31G** basis [144,145,146] for other atoms.…”

“…As demonstrated in a number of publications, heteroleptic metal alkoxides form stable binuclear complexes [69,94,97,99,140,147,148,149] that are able to catalyze ROP of cyclic esters by both binuclear and mononuclear mechanisms. DFT modeling has been shown to be an effective instrument of choice of the preferable reaction pathway.…”

Selective Degradation of End‐of‐Life Poly(lactide) via Alkali‐Metal‐Halide Catalysis

“…Noteworthy, cultivable acreage required for PLA‐plastics can be minimized. A number of investigations have been reported including the hydrolysis, alcoholysis, and (catalytic) pyrolysis or thermal degradation of PLA. For instance, the alcoholysis of PLA, especially the methanolysis, represents an interesting approach toward chemical recycling (Scheme ).…”

DFT Visualization and Experimental Evidence of BHT-Mg-Catalyzed Copolymerization of Lactides, Lactones and Ethylene Phosphates

“…Metal alkoxy complexes are effective catalysts of ring-opening polymerization (ROP); the mechanistic paradigm for ROP initiated by metal alkoxides bases on “coordination-insertion” concept [13,14,15,16,17,18,19,20] (Scheme 1b). The density functional theory (DFT) modeling was successfully applied in the mechanistic study of coordination homopolymerization of lactones [21,22,23,24,25,26,27,28,29,30,31,32,33], lactides [31,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48], cyclic carbonates [30,42,49,50] and phosphates [51].…”

“…Recently, we studied heteroleptic 2,6-di- tert -butyl-4-methylphenoxy magnesium (BHT-Mg) complexes as catalysts for the synthesis of homopolymers and block copolymers of cyclic esters and phosphates [30,31,43,51,77,78,79,80,81]. In ε -CL and LA ROP, these dimeric complexes catalyze polymerization by binuclear mechanism were closely related to the mechanism theoretically studied for di-Zn complexes [39]. The prospects of BHT-Mg complexes in the synthesis of random copolymers remain unclear.…”