Through a combined experimental and computational (DFT) approach, the reaction mechanism of the
addition of fluoroarenes to Mg–Mg bonds has been determined as a concerted SNAr-like pathway in
which one Mg centre acts as a nucleophile and the other an electrophile. The experimentally determined
Gibbs activation energy for the addition of C6F6 to a Mg–Mg bond of a molecular complex,
DG‡
298 K(experiment) ¼ 21.3 kcal mol1 is modelled by DFT with the uB97X functional, DG‡
298 K(DFT) ¼
25.7 kcal mol1
. The transition state for C–F activation involves a polarisation of the Mg–Mg bond and
significant negative charge localisation on the fluoroarene moiety. This transition state is augmented by
stabilising closed-shell Mg/Fortho interactions that, in combination with the known trends in C–F and
C–M bond strengths in fluoroarenes, provide an explanation for the experimentally determined
preference for C–F bond activation to occur at sites flanked by ortho-fluorine atoms. The effect of
modification of both the ligand coordination sphere and the nature and polarity of the M–M bond (M ¼
Mg, Zn, Al) on C–F activation has been investigated. A series of highly novel b-diketiminate stabilised
complexes containing Zn–Mg, Zn–Zn–Zn, Zn–Al and Mg–Al bonds has been prepared, including the
first crystallographic characterisation of a Mg–Al bond. Reactions of these new M–M containing
complexes with perfluoroarenes were conducted and modelled by DFT. C–F bond activation is dictated
by the steric accessibility, and not the polarity, of the M–M bond. The more open coordination
complexes lead to enhanced Mg/Fortho interactions which in turn lower the energy of the transition
states for C–F bond activation.