The Direct Oxidative Addition of O₂ to a Mononuclear Cr(I) Complex Is Spin Forbidden

Mononuclear chromium­(I) alkyne complex (<i>i</i>-Pr₂Ph)₂nacnacCr­(η²-C₂(SiMe₃)₂) (<b>1</b>) reacts rapidly with dioxygen to yield chromium­(V) dioxo species (<i>i</i>-Pr₂Ph)₂nacnacCr­(O)₂ (<b>2</b>). The mechanism of this oxygen cleavage has been studied experimentally and computationally. Isotope labeling studies rule out a direct four-electron oxidative addition of O₂ to one chromium atom, which involves a spin-forbidden transformation. Instead, the reaction likely proceeds via an unsymmetric binuclear chromium bis­(μ-oxo) complex. The latter has been independently prepared and structurally characterized. Its reactivity with O₂ is consistent with the proposed mechanism