Abstract The reactivities of the silicon-allyl bonds in two kinds of pentacoordinated silicon species CH 2 CHCH 2 Si (oO 2 C 6 H 4) 2− NMe 4+(1) and CH 2 CHCH 2-Si (OCH 2 CH 2) 3 N (2) has been compared. In the allyl transfer to carbonyl compounds under nucleophilic conditions (NaOMe, KF or Bu 4 NF) and electrophilic conditions (TiCl 4, AlCl 3, BF 3) these two species show quite different behaviour. Complex 1 is activated by ...