Varying Lewis Acidity, Covalency, and Halide Mobility to Govern Oxidative Addition Reactivity of Ni–Group 13 Bimetallic Complexes

We report two new Ni–group 13 pincer-type systems
(Ni–Al
and Ni–Ga) and describe the influence of Lewis acidity, covalency,
and halide mobility on the oxidative addition reactivity toward unsubstituted
aryl halides. Despite similar Lewis acidities of the Al- and Ga-based
metalloligands, the Ni–Ga pairing exhibits a significantly
reduced effective Lewis acidity toward triethylphosphine oxide, supported
by the greater Ni–Ga covalency as determined by density functional
theory. The higher effective Lewis acidity of Al in the Ni–Al
complex and halide mobility are required to construct the key three-membered
Ni–X–Al poised-metallacycle, an intermediate in the
oxidative addition of unsubstituted aryl halides. The Al center further
stabilizes the resulting Ni(II)–aryl product via a bridging
halide, thereby eschewing common decomposition pathways to Ni(I) byproducts.