Cooperative Reactivity Induced by All-Gallium Coordination at Nickel

Synergistic effects in mixed-metal complexes can lead
to small-molecule
activation and intriguing reactivity patterns. Herein, we report the
dimerization of acetonitrile to a nacnac-type β-diketiminate
ligand at the nickel/gallium complex fragment [Ni(GaCp*)4]2+ (Cp* = η5-C5(CH3)5). The coordination of GaCp* to the Ni(II) center leads
to strong Lewis acidity at the initially Lewis basic Ga(I) ligand,
which resembles an “umpolung” of the Ga center. The
electrophilic Ga serves as the site of bond activation. DFT calculations
indicate that the proximity of Ni and Ga and a Ga-rich coordination
sphere around the Ni atom are essential for facilitating the reaction.
Interestingly, we discovered an abnormally large kinetic isotope effect
of 28 assigned to proton tunneling.