No abstract

A novel anion exchange fuel cell membrane was successfully synthesized by chemically attaching proazaphosphatranium/phosphatranium cations under microwave treatment to the sulfonic groups of Nafion-F. Solid-state nuclear magnetic resonance (NMR) techniques were employed to determine the actual structure and composition of this anion exchange membrane. 31P NMR showed two main signals with a 2:1 intensity ratio and chemical shift changes of +89 and +46 ppm, respectively, from the main peak of phosphatranium chloride. 1H−31P heteronuclear correlation (HetCor) NMR and 1H−31P recoupling experiments indicated that the proton originally bonded to phosphorus in phosphatranium chloride is replaced in the major component of the Nafion−proazaphosphatranium/phosphatranium composite. 19F NMR experiments showed that the fluorine in the −SO2F group of the Nafion-F precursor is fully replaced. 31P{19F} rotational-echo double-resonance (REDOR) experiments measured a P−F internuclear distance of ∼0.4 nm, which showed that the proazaphosphatranium is covalently attached to Nafion through a S−P bond. 13C NMR and 1H−13C HetCor spectra indicated that the proazaphosphatranium structure is maintained even after the microwave treatment at 180 °C and also showed indications of entrapped dimethylformamide solvent.

The redox chemistry of a newly synthesized small dendrimer containing six peripheral viologen units and a phosphazene core is described. The one-electron reduction of each viologen (total six electrons) leads to intermolecular dimerization of the reduced viologens borne by the same phosphorous atom, resulting in a color change from colourless to purple providing it with potential electrochromic applications.

Herein we find that proazaphosphatrane 1c is a very efficient catalyst for Mukaiyama aldol reactions of aldehydes with trimethylsilyl enolates in THF solvent. Only the activated ketone 2,2,2-trifluoroacetophenone underwent clean aldol product formation with a variety of trimethylsilyl enolates under similar conditions as the aldehydes. The reactions were carried out at room temperature using (1-methoxy-2-methyl-1-propenyloxy)trimethylsilane, whereas the temperature was -15 degrees C in the case of 1-phenyl-1-(trimethylsilyloxy)ethylene. The reaction conditions are mild and operationally simple, and a variety of aryl functional groups, such as nitro, amino, ester, chloro, trifluoromethyl, bromo, iodo, cyano, and fluoro groups, are tolerated. Product yields are generally better than or comparable to those in the literature. 1-Phenyl-1-(trimethylsilyloxy)ethylene, 1-(trimethylsilyloxy)cyclohexene, and 2-(trimethylsilyloxy)furan underwent clean conversion to beta-hydroxy carbonyl compounds under our reaction conditions. In the case of bulky (2,2-dimethyl-1-methylenepropoxy)trimethylsilane, only alpha,beta-unsaturated esters were isolated. Heterocyclic aldehydes, such as pyridine-2-carboxaldehyde, benzofuran-2-carboxaldehyde, benzothiophene-2-carboxaldehyde, and 1-methyl-2-imidazolecarboxaldehyde, gave good yields of Mukaiyama products. An optimized synthesis for the catalyst 1c is also reported herein.