Complexes of Mg, Ca and Zn as homogeneous catalysts for lactide polymerization

Abstract

Interest in the utility of polylactide as a commodity polymer has increased significantly in recent years due to numerous environmental advantages over conventional petrochemically derived plastics. As such, the development of novel catalyst systems for the ring opening polymerization of lactide has seen tremendous progress in the past decade. In particular, divalent metals (i.e. Mg, Ca and Zn) supported by monoanionic ancillary scaffolds are appealing because of their low toxicity and cost. A much less common approach involves the use of neutral ligands in combination with the aforementioned divalent metal centres. The additional valence thus renders it possible, upon reaction with traditional Lewis or Brønsted acid activators, to generate sterically and electronically unsaturated species, akin to the most widely employed olefin polymerization catalysts. This Perspective is not intended as a comprehensive review, but rather a systematic highlight of key contributions, which have served to extend the forefront of this exciting field.

Computational Studies on the Selective Polymerization of Lactide Catalyzed by Bifunctional Yttrium NHC Catalyst

“…Many different lithium complexes have been identified as excellent catalysts for the ROP of lactides in alcohol [17]. Particularly, divalent metal catalysts bearing a monoanionic auxiliary skeleton are advantageous due to their low cost, and group 3 metal complexes are also exquisite initiators in the synthesis of PLAs by the ROP of rac-lactide [18,19]. The explicit group 4 metal complexes bearing polydentate ligands have also been proved to be active initiators for the synthesis of PLA [20].…”

Lactide polymerization with iron alkoxide complexes

“…The products [precipitate] nicely from the reaction solution as yellow or white powder." 5 Also, it is worth noting that varying the R 2 substituent on the amine can allow the synthesis of a whole spectrum of bis(imino) pyridine ligands possessing varying steric properties around the imine branches of the molecule.…”

“…Many high-activity catalysts of this type have been reported, including systems based on alkaline, earth alkaline, rare-earth and early-transition metals. 1,[5][6][7][8][9][10][11] Catalysts based on group 13 elements Al, Ga, and In often display low activities, but these systems have attracted interest thanks to their often high isoselectivity. 8,[12][13][14] With regard to late-transition-metal catalysts, the seminal work of Coates and coworkers 15 has led to extensive investigation of zinc complexes.…”

“…8,[12][13][14] With regard to late-transition-metal catalysts, the seminal work of Coates and coworkers 15 has led to extensive investigation of zinc complexes. 5 Recent reports from the Schaper group have also introduced several highly active catalysts based on Cu. [16][17][18] On the other hand, far fewer reports have appeared on development of catalytic systems based on mid-first-row transition metals.…”

Synthesis and structural characterization of LiI, ZnII, CdII, and HgII complexes containing a fluorinated β-diketiminate ligand

“…In the past decade, the use of β-diketiminates as supporting ligands was extensively studied, and a wide range of main group element [7][8][9][10][11] , transition metal [12][13][14][15][16] and lanthanide complexes [17][18] containing this type of ligands have been reported. Importantly, a good number of these metal complexes have proven to serve as effective catalysts for olefin polymerization [19] , silane dehydropolymerization [20] , olefin hydrosilylation [21] , lactide polymerization [22] , Suzuki coupling [23] , hydroamination [24] , and other transformations. Much of the related work has focused on the β-diketiminate derivatives in which the nitrogen atoms being linked with bulky substituents such as 2,6-diisopropylphenyl groups [25][26][27] .…”