Metal-ion-catalyzed σ-bond rearrangement

The metal-ion-catalyzed σ-bond rearrangement reaction occurs with highly saturated organic ring molecules treated by Ag+, Rh(I), or Pd(II) ions. Two types of the reaction were noted: [2+2] ring openings, and a conversion to another ring system:
 * [[Image:Metal-ion-catalyzed-sigma-bond-rearrangement.png|500px|Scheme 1. Metal-ion-catalyzed σ-bond rearrangement]]

A mechanism for this rearrangement reaction is not completely understood, however some explanations were suggested.