Isoselective Ring‐Opening Polymerization of rac‐Lactide Catalyzed by Sodium/potassium Tetradentate Aminobisphenolate Ion‐paired Complexes

Abstract

Twos odium/potassium tetradentate aminobisphenolate ion-paired complexes were synthesized and structurally characterized. These ion-paired complexesa re efficient catalysts for the ring-opening polymerization of rac-lactide (rac-LA) in the presence of 5equivalents BnOH as an initiator and the side reactiono fe pimerization can be suppressed well at low temperatures. The polymerizations are controllable, affording polylactidesw ith desirable molecular weights and narrow molecular weightd istributions;t he highest mo-lecular weight can reach5 0.1 kg mol À1 in this system, anda best isoselectivityo fP m = 0.82 was achieved. Such polymerizations have rarely been reported for isoselective sodium/ potassium complexes without crown ether as an auxiliary ligand.T he solid structures suggest that BnOH can be activated by an interaction with the anion of sodium/potassium complex via ah ydrogen bond and that the monomer is activated by coordinationt os odium/potassium ion.[a] X.

A One‐Pot Synthesis of “K(hfa) glyme” Adducts: Effect of the Polyether Length on the Ion Coordination Sphere

“…[14] Among alkali metals, potassium compounds are actively studied for various applications such as precursors for the metalorganic chemical vapor deposition (CVD) processes of the ferroelectric (K,Na)NbO 3, [15] the atomic layer deposition (ALD) of potassium oxide, [16] sol-gel processes to produce hybrid organic-inorganic materials [17] and in catalytic processes such as the ring-opening polymerization. [18][19][20] Potassium ion has a large ionic radius (r 6-coord = 1.51 Å), [13] which is responsible for interesting coordination moieties giving rise, in function of the coordinating ligands to extended oligomeric or polymeric network. [21][22][23] Former studies have shown that glymes play a crucial role in stabilizing complexes of alkaline-earth, [24][25][26][27][28] transition [29,30] and rare-earth metals [31,32] through oxygen-ion complexation.…”

Isoselective Polymerization of rac‐Lactide by Highly Active Sequential {ONNN} Magnesium Complexes

“…Improved polymerization rates were obtained with catalysts based on indium, [35,36] yttrium, [37,38] group 4m etals, [39,40] zinc, [41][42][43][44][45] and alkali metals. [46,47] Some of these catalysts were even found to exhibit isoselectivities that approacht hose reported for the aluminumc omplexes. The development of highly active catalysts that are also highly isoselective is still as ignificant challenge in the field of ROP catalysis.…”

“…Yet, these complexes also suffer from low polymerization rates and low turnover numbers, which prevent the production of high‐molecular‐weight PLA. Improved polymerization rates were obtained with catalysts based on indium, [35, 36] yttrium, [37, 38] group 4 metals, [39, 40] zinc, [41–45] and alkali metals [46, 47] . Some of these catalysts were even found to exhibit isoselectivities that approach those reported for the aluminum complexes.…”

Heteroleptic β-Ketoiminate Magnesium Catalysts for the Ring-Opening Polymerization of Lactide

“…Therefore, low or nontoxic metal catalyst for the ROP of cyclic esters are strongly needed . Group 1 − and 2 metals − as well as zinc − are promising candidates due to their low cost, remarkably high activity, and minimal toxicity, and among these metals, magnesium complexes are of particular interest for technical applications due to their high activity toward the ROP of cyclic esters. − The last two decades have witnessed the development of highly active mononuclear magnesium catalysts containing a large variety of monodentate, bidentate, − tridentate, − and tetradentate , ligands. In addition, dinuclear complexes containing bridging ligands − as well as multinuclear complexes have been shown to be active catalysts for the ROP of cyclic esters.…”