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

Abstract

Low-valent (MeBDI)Al and (MeBDI)Ga and highly Lewis acidic cations in [(tBuBDI)M+⋅C6H6][(B(C6F5)4−] (M=Mg or Zn, MeBDI=HC[C(Me)N-DIPP]2, tBuBDI=HC[C(tBu)N-DIPP]2, DIPP=2,6-diisopropylphenyl) react to heterobimetallic cations [(tBuBDI)Mg–Al(MeBDI)+], [(tBuBDI)Mg–Ga(MeBDI)+] and [(tBuBDI)Zn–Ga(MeBDI)+]. These cations feature long Mg–Al (or Ga) bonds while the Zn–Ga bond is short. The [(tBuBDI)Zn–Al(MeBDI)+] 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 AlI(or GaI)→Mg2+ donor bonds. Failure to isolate the Zn–Al combination originates from cleavage of the C−F bond in the solvent fluorobenzene to give (tBuBDI)ZnPh and (MeBDI)AlF+ which is extremely Lewis acidic and was not observed, but (MeBDI)Al(F)-(μ-F)-(F)Al(MeBDI)+ was verified by X-ray diffraction. DFT calculations show that the remarkably facile C–F bond cleavage follows a dearomatization/rearomatization route.