Reactivity of Cyclopropenylaluminates

Reactions of the potassium cyclopropenylaluminates, [{SiN^Dipp}-Al-η²-(C₂Ph₂)-K] and [{SiN^Dipp}-Al-η²-(PhCCSiMe₃)-K] with terminal alkynes provide alkynylvinylaluminate derivatives with the silyl-substituted analog providing a level of kinetic discrimination. While this latter behavior results in the regiochemical protonation at Al-C-(Ph) and retention of the more sterically congested Al-C-(SiMe₃) bond, reactions with CO₂ and phenyl-substituted ketones are complicated by a reduced level of discrimination and a likely tendency toward multiple CO insertion or loss of coordinated alkyne. This latter process results in reactivity more reminiscent of the Al-(I) compounds used to synthesize the cyclopropenylaluminate starting materials. Similar observations are provided by reactions with organic azides and trimethylsilyldiazomethane, which proceed with terminal nitrogen insertion and the generation of azacyclobutenylaluminate structures for [{SiN^Dipp}-Al-η²-(C₂Ph₂)-K], but with evidence of greater degrees of competitive alkyne elimination from [{SiN^Dipp}-Al-η²-(PhCCSiMe₃)-K].