Polymerization of carboxylic ester functionalized norbornenes catalyzed by (η3-allyl)palladium complexes bearing N-heterocyclic carbene ligands

Vinyl-Addition Homopolymeization of Norbornenes with Bromoalkyl Groups

Vinyl-addition polynorbornenes are of great interest as versatile templates for the targeted design of polymer materials with desired properties. These polymers possess rigid and saturated backbones, which provide them with high thermal and chemical stability as well as high glass transition temperatures. Vinyl-addition polymers from norbornenes with bromoalkyl groups are widely used as precursors of anion exchange membranes; however, high-molecular-weight homopolymers from such monomers are often difficult to prepare. Herein, we report the systematic study of vinyl-addition polymerization of norbornenes with various bromoalkyl groups on Pd-catalysts bearing N-heterocyclic carbene ligands ((NHC)Pd-systems). Norbornenes with different lengths of hydrocarbon linker (one, two, and four CH2 groups) between the bicyclic norbornene moiety and the bromine atom were used as model monomers, while single- and three-component (NHC)Pd-systems were applied as catalysts. In vinyl-addition polymerization, the reactivity of the investigated monomers varied substantially. The relative reactivity of these monomers was assessed in copolymerization experiments, which showed that the closer the bromine is to the norbornene double-bond, the lower the monomer's reactivity. The most reactive monomer was the norbornene derivative with the largest substituent (with the longest linker). Tuning the catalyst's nature and the conditions of polymerization, we succeeded in synthesizing high-molecular-weight homopolymers from norbornenes with bromoalkyl groups (Mn up to 1.4 × 106). The basic physico-chemical properties of the prepared polymers were studied and considered together with the results of vinyl-addition polymerization.

Norbornene, norbornadiene and their derivatives: promising semi-products for organic synthesis and production of polymeric materials

The methods for synthesis of promising norbornene monomers from norbornadiene and quadricyclane are summarized. A strategy for their synthesis is discussed, combining theoretical and experimental approaches to the selection of catalysts and the conditions for carrying out stereoselective reactions. The mechanisms of catalytic reactions of synthesis of norbornene monomers, as well as the progress in the macromolecular design of functional polymeric materials based on them, are considered. The data on industrial processes of production of polynorbornenes and areas of their use are presented.

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Synthesis and characterization of α-diamine palladium complexes and insight into hybridization effects of nitrogen donor atoms on norbornene (co)polymerizations

Hybridization effects of nitrogen donor atoms showed that the α-diamine palladium catalyst more easily produced highly active Pd²⁺cations for norbornene (co)polymerization.

Bypassing the lack of reactivity of endo-substituted norbornenes with the catalytic rectification-insertion mechanism

The novel rectification–insertion mechanism for the polymerization of polar norbornenes: making alternating copolymers from a single monomer.

The catalytic 1,2-insertion polymerization of polar norbornenes (NBEs) leads to the formation of functional rigid macromolecules with exceptional thermal, optical and mechanical properties. However, this remarkable reaction is plagued by the low reactivity of the polar monomers, and most notably of those bearing a functional group in endo position. We have examined the polymerization mechanism of NBEs bearing one or two CO₂Me groups either in exo or endo position catalyzed by the so-called naked allyl Pd⁺ SbF₆^– catalyst (1). Although endo dimethyl ester of 5-norbornene-2,3-dicarboxylic acid (NBE(CO₂Me)₂) is polymerized by 1, two endo units are never inserted consecutively along the polymer chain. Indeed, 1 is a tandem catalyst which not only catalyzes the insertion of the monomer but also the isomerization of endo and exo isomers. Thus, the polymerization of endo monomers proceeds via a novel mechanism, coined rectification–insertion mechanism, whereby half of the endo monomers are rectified into exo ones prior insertion, leading to the formation of an alternating endo–exo copolymer using an endo only feedstock. With this mechanism, the lack of reactivity of endo norbornenes is bypassed, and the polymerization of predominantly endo polar NBEs bearing a variety of functionalities such as esters, imides, acids, aldehydes, alcohols, anhydrides, or alkyl bromides proceeds with catalyst loadings as low as 0.002 mol%.

Synthesis, structures, and norbornene polymerization behavior of C(sp³), N-chelated palladacycles bearing o-aryloxide-N-heterocyclic carbene ligands

Treatment of the o-hydroxyaryl imidazolium pro-ligands (2-OH-3,5-tBu2C6H2)(R)(C3H3N2)(+)Br(-) [R = Mes (1a), Ph (1b), iPr (1c), Me (1d)] with Ag2O afforded the corresponding silver complexes 2a-d. Subsequent metal-exchange reactions of 2a-d with [Pd(OAc)(8-Me-quin-H)]2 (3) yielded the desired C(sp(3)), N-chelated and o-aryloxide-NHC-ligated palladacycle complexes 4a-d in 60-80% yields. When the N-tert-butyl substituted o-hydroxyaryl imidazolium pro-ligand 1e reacted with 3 in the presence of K2CO3 in dioxane, the palladacycle complex 4e, in which the NHC adopted an abnormal binding (C4-bonding), was obtained in 20% yield. All these complexes were fully characterized using (1)H and (13)C NMR spectra, high-resolution mass spectrometry (HRMS), and elemental analysis. Single-crystal X-ray diffraction analysis results further confirmed the molecular structures of 4a-c and the abnormal binding of NHC in 4e. With methylaluminoxane (MAO) as the cocatalyst these palladacycles showed excellent catalytic activities of up to 10(7) g of PNB (mol of Pd)(-1) h(-1) in the addition polymerization of norbornene.

1,4-Bis(4-bromo-2,6-diisopropyl-phen-yl)-1,4-diaza-buta-1,3-diene

The molecule of the title compound, C₂₆H₃₄Br₂N₂, lies on a crystallographic inversion center and hence the two imine groups are s-trans. The dihedral angle between the central 1,4-diaza­buta-1,3-diene unit and the attached substituted phenyl ring is 88.4 (7)°. The structure features a C—H⋯N close contact. The crystal selected for this study proved to be a non-merohedral twin with a minor component of 21.8 (3)%.

Alkene oligomerisation and polymerisation with metal-NHC based catalysts

Metal complexes of N-heterocyclic carbenes (NHCs) are now ubiquitous in homogeneous catalysis, yet their use as catalysts for oligomerisation and polymerisation of alkenes is only now gaining momentum. In recent years, a range of NHC complexes from across the transition series, and from the lanthanides, have been tested as alkene polymerisation catalysts with varying results. This perspective details the research in this field since 1998, when metal-NHC complexes were first tested for alkene polymerisation.

Synthesis of Homopolymers and Copolymers Containing an Active Ester of Acrylic Acid by RAFT: Scaffolds for Controlling Polyvalent Ligand Display

We describe the synthesis of activated homopolymers and copolymers of controlled molecular weight based on the controlled radical polymerization of N-acryloyloxysuccinimide (NAS) by reversible addition fragmentation chain transfer (RAFT). We synthesized activated homopolymers in a range of molecular weights with polydispersities between 1 and 1.2. The attachment of an inhibitory peptide to the activated polymer backbone yielded a potent controlled molecular weight polyvalent inhibitor of anthrax toxin. To provide greater control over the placement of the peptides along the polymer backbone, we also used a semi-batch copolymerization method to synthesize copolymers of NAS and acrylamide (AAm). This approach enabled the synthesis of copolymers with control over the placement of peptide-reactive NAS monomers along an inert backbone; subsequent functionalization of NAS with peptide yielded well-defined polyvalent anthrax toxin inhibitors that differed in their potencies. These strategies for controlling molecular weight, ligand density, and ligand placement will be broadly applicable for designing potent polyvalent inhibitors for a variety of pathogens and toxins, and for elucidating structure-activity relationships in these systems.