Flash Communication: The [BPh ₄ ] ⁻ Anion Is Stripped by Half-Sandwich Scandium Tetramethylaluminate Complexes

Protonolysis of the half-sandwich complex [Cp*Sc(AlMe4)Cl]2 (Cp* = C5Me5) with [Et3NH][BPh4] leads to deprotonation and rearrangement of the [BPh4]− anion to form the half-sandwich scandium boracycle complex Cp*Sc(η6-C24H19B). The new dianionic fragment [C24H19B]2– results from a B–C and C–C bond breaking/formation sequence where the boron atom has been inserted into a phenyl ring, and one carbon atom is now sp3 hybridized. Complex Cp*Sc(η6-C24H19B) was analyzed by SC-XRD, 1H, 13C{1H}, 11B{1H}, and 45Sc{1H} NMR, and elemental analysis. The high reactivity of transient the [Cp*Sc(Me)Cl] species is further tracked by the structural snapshot of a scandium 1,2,3-benztriyne complex, resulting from the reaction of partly methylated Cp’Sc(AlMe4)(Me/Cl) (Cp’ = C5Me4SiMe3) with [Et3NH][BPh4]. Both reactions illustrate new activations of the [BPh4]− anion by organo-rare-earth-metal complexes.