Yttrium‐Catalyzed Synthesis of Bipyridine‐Functionalized AB‐Block Copolymers: Micellar Support for Photocatalytic Active Rhenium‐Complexes

Abstract

Herein, ortho-methylated bipyridines are introduced as initiators in 2-aminoalkoxy-bis (phenolate) yttrium complexes. For this CÀH bond activation (ONOO) tBu Y(CH 2 TMS)(thf) (1) (TMS = trimethylsilyl) is reacted with the respective bipyridine to obtain complexes (ONOO) tBu Y(6-Me 2 bpy) (2) and (ONOO) tBu Y(6-Mebpy) (3). Both complexes were tested first in rare-earth metalmediated group-transfer polymerization of 2-vinylpridine (2VP). Complex 3 was further tested in block copolymerizations of 2VP and diethyl vinylphosphonate. The obtained initiator-P2VP-PDEVP-block copolymers can selectively react with Re(CO) 5 Cl at their bipyridine end-group. The obtained rhenium functionalized block copolymers are able to self-assemble to unimodal micelles in water, representing a possible carrier for hydrophobic metal containing complexes into cells. Furthermore, the Re-block copolymers sustain activity in the photocatalytic homogeneous CO 2 reduction and their performance exceed the catalytic activity of the analogue polymer-free system [Re(CO) 3 (6-Mebpy)Cl] (4). . CÀH bond activation of 1 with 6-Me 2 bpy and 6-Mebpy to obtain bipyridine-functionalized yttrium bis (phenolate) complexes 2 and 3.

C–H Bond Activation of Silyl-Substituted Pyridines with Bis(Phenolate)Yttrium Catalysts as a Facile Tool towards Hydroxyl-Terminated Michael-Type Polymers

“…For DEVP, the polymerization proceeds without an initiation delay in the expected fashion, however, the turnover frequency of 4320 h −1 is about one magnitude higher than reported in the literature for complex 3, indicating a different polymerization mechanism [19]. For 2VP, the normalized turnover frequency of 750 h −1 is in the same range as reported in the literature for complexes with the same ligand system [19,28,30], but in the time-conversion plot, an initiation delay of about 5 min was observed. This is in contradiction to the behavior of the other C-H bond activated catalysts reported in literature, which do not show initiation periods [28].…”

“…In this spectrum, a series of signals corresponding to m/z = [(MIni − H) + n × M2VP +H + H] + with n = 7-37 were observed, representing the 2VP oligomers functionalized with the protected initiator 2. This not only underlines a covalently bonded initiator to the polymer chain, but also further substantiates the assumed initiation mechanism of a nucleophilic attack of the methyl pyridine 2 to the first monomer unit [19,30]. As free initiator or unfunctionalized polymers would disturb a successful post-polymerization functionalization, diffusion ordered spectroscopy (DOSY) was applied.…”

“…Since the initiating groups were clearly visible in the ESI-MS, a nucleophilic transfer reaction of the initiator via a monomer insertion into an yttrium carbon bond during the initiation is evident, leading to the desired end-group (Scheme 1). Due to the exclusive presence of signals corresponding to nucleophilic transfer reaction, an initiation via deprotonation is excluded [15,19,30]. For P2VP, a MALDI-MS spectrum was recorded of purified 2VP oligomers from a reaction of catalyst 4 with 24 equivalents of 2VP in toluene ( Figure 5).…”

“…Further to this, the synthesis of block copolymers was facilitated due to the living character of this polymerization type by simple sequential addition of different monomers with respect to their coordination strength to the metal center [7,25,26]. Additionally, C-H bond activation gave access to post-polymerization functionalization and facilitated the synthesis of new block copolymer structures and polymer architectures [7,18,[27][28][29][30][31][32][33][34].…”

“…The accessibility to phosphorus-and nitrogen-containing polymers in REM-GTP, especially, poly(diethyl vinyl phosphonate) (PDEVP) with its thermoresponsive behavior and poly(2-vinylpyridine) (P2VP) with its pH-dependent solubility, highlights the potential of this polymerization type to generate smart polymers. After developing capable catalysts using C-H bond activation or catalyst immobilization, differently constituted polymers from vinyl phosphonates and/or 2VP, e.g., block copolymers as drug carriers [29,33], polymer-metal complex conjugates [30], polymer-biomolecule conjugates [31,32,41] or responsive polymer surfaces were synthesized as smart polymers so far [7,42].…”