Rearrangements and Stereomutations of Metallacycles Derived from Allenes and Imidozirconium Complexes

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.