Silylium Ion/Phosphane Lewis Pairs

The reactivity of a series of silylium ion/phosphane Lewis pairs was studied. Triarylsilylium borates 4 [B(C 6 F 5 ) 4 ] form frustrated Lewis pairs (FLPs) of moderate stability with sterically hindered phosphanes 2 . Some of these FLPs are able to cleave dihydrogen under ambient conditions. The combination of bulky trialkylphosphanes with triarylsilylium ions can be used to sequester CO 2 in the form of silylacylphosphonium ions 12 . The ability to activate molecular hydrogen by reaction of silylium ion/phosphane Lewis pairs is dominated by thermodynamic and steric factors. For a given silylium ion increasing proton affinity and increasing steric hindrance of the phosphane proved to be beneficial. Nevertheless, excessive steric hindrance leads to a breakdown of the dihydrogen-splitting activity of a silylium/phosphane Lewis pair.