Abstract
It has been proved by NMR. measurements at low temperatures that the ligand displacement reactions of (π‐all)Pd(π‐C5H5) and Lewis bases L yielding PdL4 proceed by a π → σ rearrangement of the allylic group as the primary step. The organic reaction product is the 1‐isomer of the corresponding allylcyclopentadiene but in the reactions of (π‐1,1,2‐Me3C3H2)Pd(π‐C5H5) with L besides the isomeric allylcyclopentadienes also 2,3‐dimethylbutadiene and cyclopentadiene are formed. The reaction mechanism will be discussed.