Toolbox of Nonmetallocene Lanthanides: Multifunctional Catalysts in Group-Transfer Polymerization

Herein, we present a fundamental study of isostructural 2-methoxyethylamino-bis(phenolate)-lanthanide complexes [(ONOO)^RM(X)(THF)] (M = Lu, Y; R = ^tBu, CMe₂Ph, X = CH₂TMS, collidine; THF = tetrahydrofuran; TMS = trimethylsilyl) for rare-earth metal-mediated group-transfer polymerization (GTP). This analysis includes the differentiation of electron-donating and nondonating vinyl monomers and two metal centers with regard to the ionic radius (yttrium and lutetium). In addition, highly nucleophilic alkyl initiators are compared with electron-donating heteroaromatic initiators. Our examinations include the impact of these parameters on the activity, initiator efficiency, and tacticity of the obtained polymers. Density functional theory calculations and proposed catalyst structure determinations via X-ray analysis support these investigations. This facilitates the selection of the best metal and initiator combination to address efficient and stereospecific polymerization of a broad range of Michael monomers. [(ONOO)^tBuLu(X)(THF)] shows the highest activity of 2220 h^-1 (normalized turnover frequency) for the polymerization of 2-vinylpyridine due to the higher Lewis-acidity of lutetium. Through C(sp³)-H bond activation, catalysts with higher initiator efficiency in N,N′-dimethylacrylamide (DMAA) and diethylvinylphosphonate polymerization were synthesized. Remarkably, [(ONOO)^tBuY(collidine)(THF)] was capable of stereospecifically polymerizing DMAA to highly isotactic poly(DMAA) (P_m = 0.94). Overall, the kinetics studies reveal a living-type GTP mechanism for all of the tested catalysts, enabling precise molecular-weight predeterminations with narrow molecular weight distributions (Dł ≤ 1.06).