title: A highly Lewis acidic triarylborane bearing peripheral o-carborane cages.
abstract: A triarylborane (2) bearing three o-carborane cages at peripheral positions on the aryl groups was prepared and its crystal structure was determined from X-ray diffraction study. Treatment of 2 with KF in the presence of 18-crown-6 led to the potassium salt, [2F](-). A UV-vis titration experiment carried out in THF/H(2)O (9/1 v/v) showed that 2 binds fluoride ions with a binding constant (K) of 4.8 × 10(4) M(-1), which is an order-of-magnitude greater than K for the mono-carborane substituted triarylborane. The enhanced fluoride ion affinity of 2 indicates an apparent additive effect of multiple carborane substitutions on the Lewis acidity enhancement of the triarylborane. The highly Lewis acidic nature of 2 was further utilized in evaluating the fluoride ion affinity of tris(pentafluorophenyl)borane (B(C(6)F(5))(3)). A fluoride exchange reaction between [2F](-) and B(C(6)F(5))(3) resulted in 15 times higher fluorophilicity for B(C(6)F(5))(3) than for 2. The lower Lewis acidity of 2 compared with B(C(6)F(5))(3) was confirmed from its greater cathodic reduction potential.
authors.affiliation: Department of Chemistry, KAIST, Daejeon, Republic of Korea.
authors.forename: Kang Mun
authors.initials: KM
authors.lastname: Lee
authors.forename: Jung Oh
authors.initials: JO
authors.lastname: Huh
authors.forename: Taewon
authors.initials: T
authors.lastname: Kim
authors.forename: Youngkyu
authors.initials: Y
authors.lastname: Do
authors.forename: Min Hyung
authors.initials: MH
authors.lastname: Lee