Redox initiated cationic polymerization: Silane-N-aryl heteroaromatic onium salt redox couples

Cu/Fe-mediated N(sp2)-arylation/alkenylation of pyridines with aryl-/alkenylboronic acids to yield versatile cationic materials

Cu/Fe-mediated N(sp2)-arylation/alkenylation of pyridines with aryl-/alkenylboronic acids to yield length-controllable and multi-responsive pyridinium salts is disclosed.

Silicon nanosheets as co-initiators for diaryliodonium induced radical and cationic polymerization

A system of silicon nanosheets and a diaryliodonium salt was found to initiate cationic and radical polymerizations. The polymerization relies on a syngergistic interaction between the silicon nanomaterial and the diaryliodonium salt, whereby the silicon nanomaterial acts as a co-initiator, inducing the decomposition of the diaryliodonium salt. The decomposition products, in turn, are able to initiate both cationic and radical polymerizations thereby enabling a mild and straightforward reaction procedure to obtain a variety of polymer/nanomaterial composites with cationically and radically polymerizable monomers. Most importantly, this work highlights the potential of using silicon nanomaterials' unique properties not just for physical applications, but also in chemical applications.

A Convenient N-Arylation Route for Electron-Deficient Pyridines: The Case of π-Extended Electrochromic Phosphaviologens

A simple and representative procedure for the synthesis of N,N'-diarylated phosphaviologens directly from both electron-rich and electron-poor diaryliodonium salts and 2,7-diazadibenzophosphole oxide is reported. The latter are electron-deficient congeners of the widely utilized N,N'-disubstituted 4,4'-bipyridinium cations, also known as viologens, that proved to be inaccessible by the classical two-step route. The single-step preparation method for phosphaviologens described herein could be extended to genuine viologens but reached its limit when sterically demanding diaryliodonium salts were used. The studied phosphaviologens feature a significantly lowered reduction threshold as compared to all other (phospha)viologens known to date due to the combination of an extended π-system with an electron deficient phosphole core. In addition, a considerably smaller HOMO-LUMO gap was observed due to efficient π-delocalization across the phosphaviologen core, as well as the N-aryl substituents, which was corroborated by quantum chemical calculations. Detailed characterizations of the singly reduced radical species by EPR spectroscopy and DFT calculations verified delocalization of the radical over the extended π-system. Finally, to gain deeper insight into the suitability of the new compounds as electroactive and electrochromic materials, multicolored proof-of-concept electrochomic devices were manufactured.

Benzylpyrazinium Salts as Photo-Initiators in the Polymerization of Epoxide Monomers

In order to study the capability of pyrazinium salt derivatives to act as photo-initiators of epoxide monomers, benzyl pyrazinium hexafluoroantimonate (BPH), benzyl 3,5-dimethyl pyrazine hexafluoroantimonate (BDH) and benzyl quinoxalinium hexafluoroantimonate (BQH) were synthesized by the Menschutkin reaction of benzyl bromide with pyrazine, 2,6-dimethyl pyrazine, and quinoxaline, followed by exchanging with hexafluoroantimonate (SbF₆). BPH, BDH, and BQH exhibited characteristic ultraviolet (UV) absorbance as well as exothermic peaks as a function of irradiation time in a differential photo-calorimeter (DPC). In the absence of photo-irradiation, cyclohexene oxide (CHO) underwent slow polymerization at 25 °C using BPH derivatives, but quantitative conversion was achieved even after a 5-min photo-irradiation. In addition, photo-irradiation was required for the photo-polymerization of CHO and styrene oxide (STO), which was characterized by a short induction period followed by a very rapid and exothermic polymerization. While glycidyl methyl ether (GME) required long induction periods, glycidyl phenyl ether (GPE) underwent rather slow and/or no photo-polymerization. The reactivity order of the monomers was CHO > STO >> GME >>> GPE, and the reactivity order for the photo-polymerization of CHO was BPH > BQH > BDH. It was found that BPH, BDH, and BQH could serve as photo-latent initiators for CHO, STO and GME, respectively.

Direct vicinal disubstitution of diaryliodonium salts by pyridine N-oxides and N-amidates by a 1,3-radical rearrangement

Paired off: The title reaction leads to a series of o-pyridinium phenols (1) and anilines (2). The experimental and computational studies indicate that the key step involves homolytic cleavage to give a radical pair, which undergoes solvent-cage recombination to give the product.