The Direct
Oxidative Addition of O<sub>2</sub> to
a Mononuclear Cr(I) Complex Is Spin Forbidden
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Abstract
Mononuclear
chromium(I) alkyne complex (<i>i</i>-Pr<sub>2</sub>Ph)<sub>2</sub>nacnacCr(η<sup>2</sup>-C<sub>2</sub>(SiMe<sub>3</sub>)<sub>2</sub>) (<b>1</b>) reacts rapidly with dioxygen
to yield chromium(V) dioxo species (<i>i</i>-Pr<sub>2</sub>Ph)<sub>2</sub>nacnacCr(O)<sub>2</sub> (<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 O<sub>2</sub> 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 O<sub>2</sub> is consistent with the proposed mechanism
