Solvent Effect on Bond Heterolytic Energy of Nickel Phenolate Complexes in Acetonitrile and Dimethyl Sulfoxide

Solvents can profoundly influence reaction outcomes and mechanisms through the solvation of the reaction components. Here, we determined the Ni–O bond heterolytic energy [Δ G het (Ni–O)] of nickel phenolates using dimethyl sulfoxide (DMSO) and acetonitrile (MeCN) as solvents. The results showed that Δ G het (Ni–O) in DMSO is larger than that in MeCN. This counterintuitive thermodynamics suggests that low-polarity MeCN can stabilize ionic species, generated from Ni–O bond heterolysis, more effectively than high-polarity DMSO, challenging the conventional notion of solvent polarity effects. Further experimental and theoretical studies elucidated the origin of this unique solvent effect, which cannot be observed in Pd–O systems. This work underscores the crucial role of solvents in modulating the stability of transition metal species, which can even reverse reaction thermodynamics.