Rearrangements and Stereomutations of Metallacycles Derived from Allenes and Imidozirconium Complexes MichaelForrest E. DuncanAndrew P. SweeneyZachary K. BergmanRobert G. 2005 The mechanisms of the rearrangements and stereoinversion of azametallacyclobutenes generated via [2+2] cycloaddition of allenes and imidozirconium complexes have been studied. Metallacycles derived from allenes bearing β-hydrogen atoms racemize at room temperature by reversible β-hydride elimination, a process which is also responsible for their eventual conversion to monoazadiene complexes. Metallacycles derived from diarylallenes racemize by reversible thermal bond homolysis at 95 °C; racemization of these metallacycles is also catalyzed by mild oxidants.