The proton transfer to solvent in the excited state of protonated diaminonaphthalenes, 1,5-diaminonaphthalene (1,5-DAN) and 1,8-diaminonaphthalene (1,8-DAN), in aqueous solution, has been investigated by picosecond time-resolved fluorescence measurements. The deprotonation rate constants of the dications of 1,8-DAN and 1,5-DAN in the excited state to produce the corresponding monocations are determined to be 1.3 x 10(10) and 5.6 x 10(9) s(-1), respectively, from dynamic analyses of their fluorescence time profiles. The much larger proton-dissociation rates compared with that of 1-aminonaphthalene (0.6 x 10(9) s(-1)) can be attributed to an electron-withdrawing effect due to the ammonium group at the 5- or 8-position in the naphthalene ring. The remarkably large proton-dissociation rate in 1,8-DAN can be ascribed to its larger reaction exergonicity which results from the electrostatic repulsion between the two ammonium groups in the reactant (the dication state) and the stabilization of the monocation state due to hydrogen bonding interactions between the NH3+ and NH2 moieties. The difference in their acidities in the excited state is discussed in terms of the reaction free energy and the proton affinities are evaluated from ab initio MO calculations.

We have synthesized and separated the enantiomer pair of chiral cyclotrisiloxanes for the first time. Three-blade propeller-like alignment of three phenyl groups in tri(2-butyl)triphenylcyclotrisiloxane induced a positive Cotton effect with (R)-2-butyl group, and a negative effect with (S)-2-butyl substituent.

Hexaarylcyclotrisiloxane, which is one of the most stable derivatives of diarylsilanediol, was found to undergo palladium-catalyzed cross-coupling reaction with aryl halides in good yields. The reaction is performed in an aqueous medium taking potassium hydroxide as an activator. Both of the two aryl groups attached to each silicon atom could be utilized. Some base-sensitive functionality such as acetyl and nitro groups survived the reaction.

Hexaarylcyclotrisiloxane. -Easily prepared and stable hexaarylcyclotrisiloxane is efficiently used as reagent for the Pd-catalyzed cross-coupling with aryl halides. Some base-sensitive functionalities such as acetyl and nitro groups survive the reaction. -(ENDO, M.; SAKURAI, T.; OJIMA, S.; KATAYAMA, T.; UNNO, M.; MATSUMOTO, H.; KOWASE, S.; SANO, H.; KOSUGI*, M.; FUGAMI, K.; Synlett 2007, 5, 749-752; Dep. Chem., Gunma Univ., Kiryu, Gunma 376, Japan; Eng.) -Mais 30-066