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*)] (Cp* = η-C(CH)). 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.