Cationic Heterobimetallic Mg(Zn)/Al(Ga) Combinations for Cooperative C-F Bond Cleavage.

Low-valent ( BDI)Al and ( BDI)Ga and highly Lewis acidic cations in [( BDI)M ⋅C H ][(B(C F ) ] (M=Mg or Zn, BDI=HC[C(Me)N-DIPP] , BDI=HC[C(tBu)N-DIPP] , DIPP=2,6-diisopropylphenyl) react to heterobimetallic cations [( BDI)Mg-Al( BDI) ], [( BDI)Mg-Ga( BDI) ] and [( BDI)Zn-Ga( BDI) ]. These cations feature long Mg-Al (or Ga) bonds while the Zn-Ga bond is short. The [( BDI)Zn-Al( BDI) ] cation was not formed. Combined AIM and charge calculations suggest that the metal-metal bonds to Zn are considerably more covalent, whereas those to Mg should be described as weak Al (or Ga )→Mg donor bonds. Failure to isolate the Zn-Al combination originates from cleavage of the C-F bond in the solvent fluorobenzene to give ( BDI)ZnPh and ( BDI)AlF which is extremely Lewis acidic and was not observed, but ( BDI)Al(F)-(μ-F)-(F)Al( BDI) was verified by X-ray diffraction. DFT calculations show that the remarkably facile C-F bond cleavage follows a dearomatization/rearomatization route.