Polysulfone main chains have been functionalized with hypersulfonated aromatic side chains where the sulfonic acid groups were highly concentrated on a local scale, with two acid groups placed on the same aromatic ring. This molecular design was implemented to promote the nanophase separation that takes place in proton-exchange membranes between the hydrophobic polymer main chain and the hydrophilic ionic groups responsible for the water uptake and conduction. Morphological investigations revealed that polysulfones functionalized with disulfonaphthoxybenzoyl or trisulfopyrenoxybenzoyl side chains contained larger and more uniform ionic clusters, as compared to conventionally sulfonated polysulfones where the acid groups are dispersed along the main chain. Membranes based on the polymers carrying hypersulfonated side chains formed efficient networks of water-filled nanopores upon hydration, which facilitated excellent levels of proton conductivity exceeding that of the commercial Nafion membrane at moderate water uptakes.

Proton-Conducting Aromatic Polymers Carrying Hypersulfonated Side Chains for Fuel Cell Applications†

Mechanically strong and flexible membranes with very high local concentrations of immobilized proton-conducting phosphonic acid have been achieved by grafting poly(vinylphosphonic acid) side chains onto polysulfones. The graft copolymers were prepared by anionic polymerization of diethyl vinylphosphonate initiated from lithiated polysulfones, followed by quantitative cleavage of the ester functions. The resulting phosphonic acid units acted like monoprotic acids to indicate a high level of intramolecular interactions, and the phase-separated nature of the copolymers was shown by dual glass transitions. Fully polymeric membranes were conveniently cast from solution and showed high proton conductivities, e.g., 5 mS/cm under nominally dry conditions at 120 °C and up to 93 mS/cm under 100% relative humidity at the same temperature. The corresponding conductivities measured for Nafion 115 under the same conditions were 0.04 and 105 mS/cm, respectively. The former membranes furthermore showed high thermal stabi...

Polysulfones grafted with poly(vinylphosphonic acid) for highly proton conducting fuel cell membranes in the hydrated and nominally dry state

A comprehensive study of the enantioselective Pd-catalyzed α-arylation of N-Boc pyrrolidine has been carried out. The protocol involves deprotonation of N-Boc pyrrolidine using s-BuLi/(−)-sparteine in TBME or Et2O at −78 °C, transmetalation with ZnCl2 and Negishi coupling using Pd(OAc)2, t-Bu3P-HBF4 and the aryl bromide. This paper reports several new features including in situ React IR spectroscopic monitoring of the process; use of (−)-sparteine and the (+)-sparteine surrogate to access products with opposite configuration; development of a catalytic asymmetric lithiation–Negishi coupling reaction; extension to a wide range of heteroaromatic bromides; total synthesis of (R)-crispine A, (S)-nicotine and (S)-SIB-1508Y via short synthetic routes; and examples of α-vinylation of N-Boc pyrrolidine using vinyl bromides exemplified by the total synthesis of naturally occurring (+)-maackiamine (thus establishing its configuration as (R)). In this way, the full scope and limitations of the methodology are deline...

Enantioselective, palladium-catalyzed α-arylation of N-Boc pyrrolidine: in situ react IR spectroscopic monitoring, scope, and synthetic applications.

Systematic studies are presented demonstrating the complementarity of directed ortho metalation (DoM) and Ir-catalyzed strategies for the provision of borylated aromatics and their subsequent Suzuki-Miyaura coupling reactions. A new concept, the use of the TMS group, readily introduced by DoM, as a latent regiodirective moiety to overcome the otherwise problematic production of isomeric borylated product mixtures is presented. Additional electrophile-induced ipso-deborylation and DoM reactions of the Bpin products are described.

Iridium-catalyzed C-H activation versus directed ortho metalation: complementary borylation of aromatics and heteroaromatics.

A set of novel phosphine-phosphorami- dite ligands possessing two elements of chirality have been prepared through a modular synthetic approach. The ligands (11bS)-N-(2-(diphenylphos- phino)phenyl)-N-((S)-1-phenylethyl)dinaphtho(2,1- d:1',2'-f)Aphepin-4-amine ((Sa,Sc)-1a) and (11bR)-N-(2-(diphenylphosphino)phenyl)-N- ((S)-1-(1-naphthyl)ethyl)dinaphtho(2,1-d:1',2'-f)- Aphepin-4-amine ((Sa,Sc)-1b) are unique in providing enantioselectivities 96% ee and 94% ee, respectively, in mechanistically dis- tinct hydrogenations of C=C, C= Na nd C=O double bonds in combination with three different transition metals (rhodium, iridium, and ruthenium, respec- tively). Particularly remarkable are the enantiomer- ic excesses up to 97% achieved in the iridium-cata- lyzed hydrogenation of 2-substituted quinolines, where (11bS)-N-(2-(diphenylphosphino)phenyl)-N-

Highly Efficient and Versatile Phosphine-Phosphoramidite Ligands for Asymmetric Hydrogenation

Titration of alkyllithiums with a simple reagent to a blue endpoint

The effect of protecting groups on tin-lithium exchange in α-alkoxyalkyltrimethylstannanes

Resolution of α-hydroxystannanes via norephedrine carbamates

MOM-protected α-hydroxytrimethylstannanes do not undergo tin-lithium exchange cleanly as their tributyl-counterparts do. Other protecting groups (e.g. N,N-diethylcarbamate) allow for clean transmetalation to occur presumably due to the formation of a more stable α-alkoxyorganolithium species.

Nathan Nielsen

Papers

Titration of alkyllithiums with a simple reagent to a blue endpoint

The effect of protecting groups on tin-lithium exchange in α-alkoxyalkyltrimethylstannanes

Resolution of α-hydroxystannanes via norephedrine carbamates

The Effect of Protecting Groups on Tin—Lithium Exchange in α-Alkoxyalkyltrimethylstannanes.