No abstract

The design and functionalization of reaction space around catalytic centers may promote catalysis. [1][2][3] With their unique three-dimensional globular structures, microgel-core star polymers [4][5][6][7][8] are intriguing as scaffolds that enclose catalysts: the central core is not only compartmentalized by linear-arm polymers but is also locally heterogeneous (cross-linked network), while the molecule as a whole is completely homogeneous and soluble through its soluble surrounding arms. Given these features, core-functionalized star polymers [5][6][7][8] have been developed as a new type of macromolecularly supported catalysts with a unique reaction space. For example, we have synthesized such star polymer catalysts by metal-catalyzed living radical polymerization [9,10] (Scheme 1) by in situ direct encapsulation ("tandem catalyst interchange") of ruthenium complexes into the microgel core that carries multiple phosphine ligands.[5] These "metalbearing" star polymers efficiently catalyzed hydrogen-transfer reactions with high activity, versatility, and recyclability, in comparison to their homogeneous or polymer-supported counterparts.[3]Herein, we report living radical polymerization in microgel-core reaction vessels of metal-bearing star polymers obtained by tandem catalyst interchange (Scheme 1). These star catalysts are well soluble, but the metal complexes are caged (i.e., protected) within the microgel network and lead to high activity and stability, functionality tolerance, and catalyst recycling, among others. This work is to demonstrate that the star-catalyzed system enables a novel homogeneous compartmentalized polymerization in a catalyst-embedded core, which is to be clearly distinguished from the polymerizations with conventional polymer-supported insoluble catalysts [11] and those in heterogeneous dispersed or emulsion systems particularly in terms of catalytic activity, functionality tolerance, and recyclability, among other feartures expected. [12] To successfully apply star polymer catalysts to the polymerization, PPh 3 -star S3 was synthesized by a one-pot tandem route consisting of: 1) the synthesis of RuCl 2 -Star S1 by the ruthenium-catalyzed linking reaction of linear-arm polymers with a binfunctional linker 1 and a ligand comonomer 2; [5] 2) the in situ hydrogenation [13] of the corebound chlorine and olefin units within S1 to give hydrogenated star S2, and 3) the removal of the core-bound ruthenium complexes from S2 leading to an empty-core star S3 with nonligating phosphines. Then, new metal complexes were introduced into the core of S3, giving metal-star catalysts such as RuCp*-Star S4 to be directly employed for living polymerization. Hence, the original polymerization catalyst [RuCl 2 (PPh 3 ) 3 ] is first core-bound and then interchanged with a new complex [e.g., RuCp* or FeBr 2 ], all in situ and in one pot. Note that step (2) serves to eliminate the potentially growth-active or reactive units (halogen and olefin, respectively) from the core. The products were characterized by si...

Multifunctional microgel-core star polymers with ruthenium catalysts are designed as catalyst-bearing nanoreactors to improve activity, controllability, and functionality tolerance in living radical polymerization. Multifunctional ligands are efficiently incorporated into the core of star polymers by sequential tandem procedures: 1) ruthenium-catalyzed living radical polymerization, 2) in situ core hydrogenation, and 3) core-ruthenium removal. Typically, the star polymer ligands comprising multiple phosphines and amines within the core cooperatively enclose a ruthenium complex (>100 per core). As a result, the in-core pseudo hetero P,N-chelation of the ruthenium complexes not only showed high activity for methyl methacrylate but also high tolerance to unprotected methacrylic acid.

Sterne mit Metallkern: Vielseitige Sternpolymer‐Katalysatoren mit Mikrogelkern‐Reaktionsgefäßen wurden durch Katalysatoraustausch und Ru‐katalysierte lebende radikalische Polymerisation, In‐situ‐Hydrierung und Entfernen und Einfügen von Metallen erhalten. Dank der Einkapselung des Katalysators in dieser Umgebung zeigen die Sternkatalysatoren hohe Aktivität, Vielseitigkeit, Toleranz für funktionelle Gruppen und Rezyklierbarkeit in lebenden radikalischen Polymerisationen.