C–H Bond Activation by σ-Bond Metathesis as a Versatile Route toward Highly Efficient Initiators for the Catalytic Precision Polymerization of Polar Monomers

Merging σ-Bond Metathesis with Polymerization Catalysis: Insights into Rare-Earth Metal Complexes, End-Group Functionalization, and Application Prospects

Polymers with well-defined structures, synthesized through metal-catalyzed processes, and having end groups exhibiting different polarity and reactivity than the backbone, are gaining considerable attention in both scientific and industrial communities. These polymers show potential applications as fundamental building blocks and additives in the creation of innovative functional materials. Investigations are directed toward identifying the most optimal and uncomplicated synthetic approach by employing a combination of living coordination polymerization mediated by rare-earth metal complexes and C-H bond activation reaction by σ-bond metathesis. This combination directly yields catalysts with diverse functional groups from a single precursor, enabling the production of terminal-functionalized polymers without the need for sequential reactions, such as termination reactions. The utilization of this innovative methodology allows for precise control over end-group functionalities, providing a versatile approach to tailor the properties and applications of the resulting polymers. This perspective discusses the principles, challenges, and potential advancements associated with this synthetic strategy, highlighting its significance in advancing the interface of metalorganic chemistry, polymer chemistry, and materials science.

A graft-to strategy of poly(vinylphosphonates) on dopazide-coated gold nanoparticles using in situ catalyst activation

A modular synthetic pathway for poly(diethyl vinylphosphonates) grafting-to gold nanoparticles is presented. Utilising an azide-dopamine derivative as nanoparticle coating agent, alkyne-azide click conditions were used to covalently tether the polymer to gold nanoparticles leading to stable and well distributed colloids for different applications.

The Role of Chemically Innocent Polyanions in Active, Chemically Fueled Complex Coacervate Droplets

Complex coacervation describes the liquid-liquid phase separation of oppositely charged polymers. Active coacervates are droplets in which one of the electrolyte's affinity is regulated by chemical reactions. These droplets are particularly interesting because they are tightly regulated by reaction kinetics. For example, they serve as a model for membraneless organelles that are also often regulated by biochemical transformations such as post-translational modifications. They are also a great protocell model or could be used to synthesize life-they spontaneously emerge in response to reagents, compete, and decay when all nutrients have been consumed. However, the role of the unreactive building blocks, e.g., the polymeric compounds, is poorly understood. Here, we show the important role of the chemically innocent, unreactive polyanion of our chemically fueled coacervation droplets. We show that the polyanion drastically influences the resulting droplets' life cycle without influencing the chemical reaction cycle-either they are very dynamic or have a delayed dissolution. Additionally, we derive a mechanistic understanding of our observations and show how additives and rational polymer design help to create the desired coacervate emulsion life cycles.

Design, Synthesis and Actual Applications of the Polymers Containing Acidic P-OH Fragments: Part 2-Sidechain Phosphorus-Containing Polyacids

Macromolecules containing acidic fragments in side-groups—polyacids—occupy a special place among synthetic polymers. Properties and applications of polyacids are directly related to the chemical structure of macromolecules: the nature of the acidic groups, polymer backbone, and spacers between the main chain and acidic groups. The chemical nature of the phosphorus results in the diversity of acidic >P(O)OH fragments in sidechain phosphorus-containing polyacids (PCPAs) that can be derivatives of phosphoric or phosphinic acids. Sidechain PCPAs have many similarities with other polyacids. However, due to the relatively high acidity of −P(O)(OH)2 fragment, bone and mineral affinity, and biocompatibility, sidechain PCPAs have immense potential for diverse applications. Synthetic approaches to sidechain PCPAs also have their own specifics. All these issues are discussed in the present review.

Poly(2-isopropenyl-2-oxazoline) as a reactive polymer for materials development

Poly(2-isopropenyl-2-oxazoline) has attracted growing interest as a reactive polymer that can be used as a starting material for the construction of more complex structures.

Synthesis, characterisation and functionalisation of BAB-type dual-responsive nanocarriers for targeted drug delivery: evolution of nanoparticles based on 2-vinylpyridine and diethyl vinylphosphonate

The emerging field of nanomedicine gives new opportunities in the treatment of cancer. Aspects such as dosage, bioavailability or the application to the patient can be drastically improved. Previously our group reported an efficient route towards cross-linked nanospheres based on ABB' block copolymers made from 2-vinylpyridine (2VP), diethyl vinylphosphonate (DEVP) and diallyl vinylphosphonate (DAlVP). Followed by thiol-ene click chemistry stable nanoparticles were formed. Herein, this promising concept was extended to copolymers with the analogous B'BABB' architecture. In this context the new yttrium complex 5 was investigated in the rare-earth metal-mediated group transfer polymerisation (REM-GTP) and used for the generation of copolymers with different monomer feeds (2VP: 100-300 equiv.; DEVP: 200-300 equiv.; DAlVP: 6-20 equiv.) to explore the influence of the copolymer compositon on the nanoparticle properties. After successful cross-linking with various cross-linking agents, all nanoparticles were characterised via DLS and TEM. These size measurements revealed defined, almost spherical particles (d DLS = 17-52 nm; d TEM = 17-43 nm) and were mainly affected by the 2VP content and the cross-linking density. Zeta potential measurements resulted in values in the range from -6 mV to -22 mV and revealed an influence of the cross-linking agent on the surface charge. Studies on the release behaviour exhibited the fastest release at pH = 4.5. Temperature-wise best results were achieved at 42 °C. Furthermore, we aimed for the conjugation of folic acid as a model compound for a potential application in active drug targeting. The consecutive couplings of cysteamine and dithiol 6 enabled the formation of an amine-modified precursor which was reacted with a folic acid derivative. Zeta potential measurements and analysis by NMR spectroscopy corroborated a successful conjugation while DLS and TEM (d DLS = 44 nm; d TEM = 38 nm) indicated defined nanoparticles.

Allyl group-containing polyvinylphosphonates as a flexible platform for the selective introduction of functional groups via polymer-analogous transformations

Polyvinylphosphonates are highly promising candidates for (bio)medical applications as they exhibit a tunable lower critical solution temperature, high biocompatibility of homo- and copolymers, and a broad foundation for post-synthetic modifications. In this work we explored polymer-analogous transformations with statistical polyvinylphosphonates comprising diethyl vinylphosphonate (DEVP) and diallyl vinylphosphonate (DAlVP). The C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C double bonds were used as a starting point for a cascade of organic transformations. Initially, the reactive moieties were successfully introduced via bromination, epoxidations with OXONE and mCPBA, or thiol–ene click chemistry with methyl thioglycolate (6). The obtained substrates were then employed in a variety of consecutive reactions depending on the introduced functional motif: (1) the brominated substrates were converted with sodium azide to enable the copper-mediated alkyne–azide coupling with phenylacetylene (1). (2) The epoxides were reacted with sodium azide for an alkyne–azide click coupling with 1 as well as small nucleophilic compounds (phenol (2), benzylamine (3), and 4-amino-2,1,3-benzothiadiazol (4)). Afterwards the non-converted allyl groups were reacted with thiochloesterol (5) to form complex polymer conjugates. (3) An acid-labile hydrazone-linked conjugate was formed in a two-step approach. The polymeric substrates were characterized by NMR, FTIR, and UV/Vis spectroscopy as well as elemental analysis and gel permeation chromatography to monitor the structural changes of the polymeric substrates and to prove the success of these modification approaches.

A rich functionalization chemistry was established starting from defined, allyl group containing polyvinylphosphonates.

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

Herein, silicon-protected, ortho-methylated hydroxy-pyridines were reported as initiators in 2-aminoalkoxy-bis(phenolate)yttrium complexes for rare earth metal-mediated group-transfer polymerization (REM-GTP) of Michael-type monomers. To introduce these initiators, C−H bond activation was performed by reacting [(ONOO)tBuY(X)(thf)] (X = CH2TMS, thf = tetrahydrofuran) with tert-butyl-dimethyl-silyl-functionalized α-methylpyridine to obtain the complex [(ONOOtBuY(X)(thf)] (X = 4-(4′-(((tert-butyldimethylsilyl)oxy)methyl)phenyl)-2,6-di-methylpyridine). These initiators served as functional end-groups in polymers produced via REM-GTP. In this contribution, homopolymers of 2-vinylpyridine (2VP) and diethyl vinyl phosphonate (DEVP) were produced. Activity studies and end-group analysis via mass spectrometry, size-exclusion chromatography (SEC) and NMR spectroscopy were performed to reveal the initiator efficiency, the catalyst activity towards both monomers as well as the initiation mechanism of this initiator in contrast to commonly used alkyl initiators. In addition, 2D NMR studies were used to further confirm the end-group integrity of the polymers. For all polymers, different deprotection routes were evaluated to obtain hydroxyl-terminated poly(2-vinylpyridine) (P2VP) and poly(diethyl vinyl phosphonate) (PDEVP). Such hydroxyl groups bear the potential to act as anchoring points for small bioactive molecules, for post-polymerization functionalization or as macroinitiators for further polymerizations.

Heteronuclear, Monomer-Selective Zn/Y Catalyst Combines Copolymerization of Epoxides and CO2 with Group-Transfer Polymerization of Michael-Type Monomers

Terpolymerizations of cyclohexene oxide (CHO), CO₂, and the Michael-type monomer 2-vinylpyridine (2VP) are presented. The combination of two distinct polymerization mechanisms was enabled by the synthesis of a heterobifunctional complex (3). Its β-diiminate zinc moiety allows the ring-opening copolymerization of CHO and CO₂, whereas the yttrium metallocene catalyzed the rare earth metal-mediated group-transfer polymerization of the polar vinyl monomer. Both units were connected via the CH-bond activation of a pyridyl-alkoxide linker. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) revealed the successful transfer of the linker to the end-group of the respective homopolymers poly(cyclohexene carbonate) (PCHC) and poly(2VP) (P2VP) being the prerequisite for copolymer formation. Aliquot gel-permeation chromatography (GPC) analysis and solubility behavior tests confirmed the P2VP-block(b)-PCHC terpolymer formation via two pathways, a sequential and a one-pot procedure. Furthermore, the versatility of the method was demonstrated by introducing 2-isopropenyl-2-oxazoline (IPOx) as the second Michael-type monomer that yielded the terpolymer poly(IPOx)-b-PCHC.

Rare earth metal-mediated ring-opening polymerisation of cyclic phosphoesters

An efficient polymerisation of cyclic phosphoesters using a rare-earth metallocene as a catalyst is described, giving biodegradable polyphosphonates and polyphosphates.

Synthesis of next generation dual-responsive cross-linked nanoparticles and their application to anti-cancer drug delivery

Rare earth metal-mediated group transfer polymerisation enables the synthesis of previously inaccessible block copolymers of 2-vinylpyridine, diethyl vinylphosphonate and the new diallyl vinylphosphonate monomer. This precision polymerisation and the selective cross-linking of allyl side groups via thiol-ene click chemistry leads to the formation of well-defined dual-responsive nanoparticles. We demonstrate that these next generation nanocarriers are pH- and temperature-responsive and are capable of efficiently delivering doxorubicin into the nucleus of cancer cells. High anti-cancer activity could be demonstrated via cytotoxicity tests on breast cancer (MCF-7) and cervical cancer (HeLa) cells. These results validate this modular synthesis route as an ideal platform for the development of sophisticated nanocarriers for future drug delivery applications.

Functional Precision Polymers via Stereo- and Regioselective Polymerization Using Group 6 Metal Alkylidene and Group 6 and 8 Metal Alkylidene N-Heterocyclic Carbene Complexes

The concepts of functional precision polymers and the latest accomplishments in their synthesis are summarized. Synthetic concepts based on chain growth polymerization are compared to iterative synthetic approaches. Here, the term "functional precision polymers" refers to polymers that are not solely hydrocarbon-based but contain functional groups and are characterized by a highly ordered primary structure. If insertion polymerization is used for their synthesis, olefin metathesis-based polymerization techniques, that is, ring-opening metathesis polymerization (ROMP), acyclic diene metathesis (ADMET) polymerization, and the regio- and stereoselective cyclopolymerization of α,ω-diynes are almost exclusively applied. Particularly with regio- and stereospecific ROMP and with cyclopolymerization, the synthesis of tactic polymers and copolymers with high regio-, stereo-, and sequence control can be accomplished; however, it requires carefully tailored transition metal catalysts. The fundamental synthetic concepts and strategies are outlined.

Studies on the Biocompatibility of Poly(diethyl vinyl-phosphonate) with a New Fluorescent Marker

Utilization of group transfer polymerization for the synthesis of poly(diethyl vinylphosphonate) (PDEVP) allows its controlled end-group functionalization. Thus, a new fluorescent chromophore/PDEVP conjugate is prepared and subjected to biocompatibility tests on two different human cell lines. In contrast to the previous studies, the tagged polymer is not absorbed by cells from the solution and has nearly no impact on cell mortality rate.

Metal-Catalyzed Group-Transfer Polymerization: A Versatile Tool for Tailor-Made Functional (Co)Polymers

Accommodating the increasing demand for tailor-made polymers is a major goal in polymer chemistry. Therefore, the investigation of polymerization techniques, which allow the precise synthesis of macromolecules is of exceptional interest. Ionic or controlled radical polymerization are capable living-type methods for the generation of uniform polymers. However, even these approaches reach their limits in certain issues. In the last decades, group-transfer polymerization (GTP) and especially metal-catalyzed GTP have proven to give access to a plethora of tailor-made homo- and copolymers based on α,β-unsaturated monomers. Thereby, GTP has established its potential in the development of functional and smart polymers. This concept article highlights the most significant progress in metal-catalyzed GTP with a focus on functional (co)polymers including different polymeric architectures and microstructures.

Versatile reactivities of rare-earth metal dialkyl complexes supported by a neutral pyrrolyl-functionalized β-diketiminato ligand

The first unprecedented examples of S-β-diketiminato species were disclosed in the reactions of rare-earth dialkyl complexes with S₈.

Precise synthesis of thermoresponsive polyvinylphosphonate-biomolecule conjugatesviathiol–ene click chemistry

Herein we present the first smart polyvinylphosphonate-bioconjugates obtainedviaan efficient modular synthetic route.

Regioselective addition of C(sp3)–H bonds of alkyl pyridines to olefins catalysed by cationic zirconium complexes

The first group 4 metal catalysts are developed to catalyse C(sp³)–H addition of alkyl pyridines to olefins. Ligand-controlled regioselectivity was observed and verified.

Multiresponsive micellar block copolymers from 2-vinylpyridine and dialkylvinylphosphonates with a tunable lower critical solution temperature

Tailor-made, multi-responsive micellar AB and ABB′ block copolymers show a pH-sensitivity and a tunable LCST within an expanded temperature range.