title: Slow reactant-water exchange and high catalytic performance of water-tolerant Lewis acids.
abstract: (31)P nuclear magnetic resonance (NMR) spectroscopic measurement with trimethylphosphine oxide (TMPO) was applied to evaluate the Lewis acid catalysis of various metal triflates in water. The original (31)P NMR chemical shift and line width of TMPO is changed by the direct interaction of TMPO molecules with the Lewis acid sites of metal triflates. [Sc(OTf)3] and [In(OTf)3] had larger changes in (31)P chemical shift and line width by formation of the Lewis acid-TMPO complex than other metal triflates. It originates from the strong interaction between the Lewis acid and TMPO, which results in higher stability of [Sc(OTf)3TMPO] and [In(OTf)3TMPO] complexes than other metal triflate-TMPO complexes. The catalytic activities of [Sc(OTf)3] and [In(OTf)3] for Lewis acid-catalyzed reactions with carbonyl compounds in water were far superior to the other metal triflates, which indicates that the high stability of metal triflate-carbonyl compound complexes cause high catalytic performance for these reactions. Density functional theory (DFT) calculation suggests that low LUMO levels of [Sc(OTf)3] and [In(OTf)3] would be responsible for the formation of stable coordination intermediate with nucleophilic reactant in water.
authors.affiliation: Materials and Structures Laboratory, Tokyo Institute of Technology, Nagatsuta, Midori-ku Yokohama 226-8503 (Japan); Research Fellow of Japan Society for the Promotion of Science (JSPS), 5-3-1 Chiyoda-ku, Tokyo 102-0083 (Japan).
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Koito
authors.forename: Kiyotaka
authors.initials: K
authors.lastname: Nakajima
authors.forename: Hisayoshi
authors.initials: H
authors.lastname: Kobayashi
authors.forename: Ryota
authors.initials: R
authors.lastname: Hasegawa
authors.forename: Masaaki
authors.initials: M
authors.lastname: Kitano
authors.forename: Michikazu
authors.initials: M
authors.lastname: Hara
keywords: Lewis acids; NMR spectroscopy; carbonyl compounds; density functional calculations; metal triflates