Preparation of a chiral ferrocenyl derivative containing a biphenyl unit via nickel-mediated homocoupling

Ferrocenyl derivative 2, which possesses a biphenyl unit, was prepared by nickel(0)-mediated homocoupling of a chiral ferrocenyloxazoline. Compound 2 exists as an equilibrium mixture of two diastereomers, in a ratio dependent on temperature and solvent, due to the partially hindered rotation around biaryl bond. Upon complexation with Cu(I) or Zn(II), complete fixation of the stereogenic axis was obtained and a single stable atropoisomer was formed, whose absolute configuration was assigned on the basis of its NOESY spectrum. The 2-Cu(I) complex was used as catalyst in the cyclopropanation of styrene.