title: A Janus-headed Lewis superacid: simple access to, and first application of Me3Si-F-Al(OR(F))3.
abstract: Upon reaction of gaseous Me3SiF with the in situ prepared Lewis acid Al(OR(F))3, the stable ion-like silylium compound Me3 Si-F-Al(OR(F))3 1 forms. The Janus-headed 1 is a readily available smart Lewis acid that differentiates between hard and soft nucleophiles, but also polymerizes isobutene effectively. Thus, in reactions of 1 with soft nucleophiles (Nu), such as phosphanes, the silylium side interacts in an orbital-controlled manner, with formation of [Me3Si-Nu](+) and the weakly coordinating [F-Al(OR(F))3](-) or [((F)RO)3Al-F-Al(OR(F))3](-) anions. If exchanged for hard nucleophiles, such as primary alcohols, the aluminum side reacts in a charge-controlled manner, with release of FSiMe3 gas and formation of the adduct R(H)O-Al(OR(F))3. Compound 1 very effectively initiates polymerization of 8 to 21 mL of liquid C4 H8 in 50 mL of CH2 Cl2 already at temperatures between -57 and -30 °C with initiator loads as low as 10 mg in a few seconds with 100% yield but broad polydispersities.
authors.affiliation: Institut für Anorganische und Analytische Chemie, Freiburger Materialforschungszentrum (FMF) and Freiburg Institute for Advanced Studies (FRIAS), Section Soft Matter Science, Universität Freiburg, Albertstrasse 19, 79104 Freiburg (Germany).
authors.forename: Michael
authors.initials: M
authors.lastname: Rohde
authors.forename: Lutz O
authors.initials: LO
authors.lastname: Müller
authors.forename: Daniel
authors.initials: D
authors.lastname: Himmel
authors.forename: Harald
authors.initials: H
authors.lastname: Scherer
authors.forename: Ingo
authors.initials: I
authors.lastname: Krossing
keywords: Lewis acids; density functional calculations; nucleophiles; silylium; weakly coordinating anions