# Cooperative Reactivity Induced by All-Gallium Coordination at Nickel

## TL;DR

A nickel-gallium complex enables unique reactivity through cooperative effects, activating bonds and showing a large isotope effect due to proton tunneling.

## Contribution

Discovery of a nickel-gallium complex with cooperative reactivity and a large kinetic isotope effect from proton tunneling.

## Key findings

- The nickel/gallium complex [Ni(GaCp*)4]2+ activates acetonitrile through cooperative reactivity.
- The gallium center exhibits reversed (umpolung) Lewis acidity due to nickel coordination.
- A large kinetic isotope effect of 28 is attributed to proton tunneling in the reaction.

## Abstract

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.