▪ Abstract  Anhydrous proton-conducting polymers usually consist of a more or less inert polymer matrix that is swollen with an appropriate proton solvent (in most cases, phosphoric acid). An outline of the different materials is provided, with a focus on PBI/H3PO4 blends that are currently most suitable for fuel cell applications. Also discussed are alternative concepts for fully polymeric materials, which establish proton conductivity as an intrinsic property using amphoteric heterocycles such as imidazole as a proton solvent. The development of some of the first polymers is described, and the fundamental relations between their material properties and conductivity are discussed. Closely related to this relatively new concept are mechanistic investigations focusing on intermolecular proton transfer and diffusion of (protonated) solvent molecules, the contributions of both transport processes to conductivity, and the dependence of these ratios on composition, charge carrier density, etc. Although the development of fully polymeric proton conductors is inseparably related to mechanistic considerations, relatively little attention has been paid to these concepts in the field of conventional membranes (hydrated ionomers, H3PO4-based materials). Consequently, their general relevance is emphasized, and according investigations are summarized to provide a more comprehensive picture of proton transport processes within proton exchange membranes.

High-resolution solid-state 1H NMR under fast magic angle spinning is used for the first time to study proton conductivity. The materials of interest, ethylene oxide tethered imidazole heterocycles (Imi-nEO), are characterized by variable temperature experiments, as well as 2D homonuclear double quantum (DQ) NMR and 2D exchange spectroscopy. Quantum chemical calculations provide a full assignment and understanding of the 1H chemical shifts, based on a single-crystal structure obtained for Imi-2EO. Three types of hydrogen-bonded N-1H resonances are observed by 1H MAS NMR at 30 kHz. Double quantum NMR experiments identify those hydrogen-bonded protons that are mobile on the time scale of the experiment, and thereby, those which are able to participate in charge transport. Characterized by their spin−spin relaxation ( ) behavior, the local mobility of these protons as a function of temperature is compared to the conductivity of the materials. Homonuclear 1H 2D DQ MAS spectra provide evidence for locally ordered domains within all the Imi-nEO materials. Disordered (mobile) and ordered components in Imi-2EO dramatically differ in their 1H spin−lattice relaxation times. 2D NOESY spectra show no evidence of chemical exchange processes between the ordered and disordered domains. These results indicate that the highly ordered regions of the materials do not (or only poorly) contribute to proton conductivity, which is rather taking place in the disordered regions. Molecules in the disordered domains are in a state of dynamic or fluctuating hydrogen-bonding, allowing for Grotthus mechanism proton transport, while molecules in the ordered domains do not experience exchange, and do not participate in long-range proton conductivity. At the interface between these regimes a small number of molecules undergo slow exchange. With increasing temperature, this exchange becomes fast on the NMR time scale, and the final chemical shift of 12.5 ppm in Imi-5EO implies the persistence of strongly and weakly hydrogen-bonded domains, which reorganize rapidly to support the proton transport process.

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A series of ortho-substituted chiral hypervalent iodine reagents has been synthesized utilizing a zirconium-mediated iodoacylation reaction, which was followed by a stereoselective reduction, methylation, and an oxidation/ligand-exchange sequence. The evaluation of these new compounds as stereoselective electrophilic reagents towards alkenes and ketones is reported. Enantioselectivities as high as 65% have been achieved in the dioxytosylation of styrene and of up to 40% in the oxytosylation of propiophenone. X-ray structure