A Nucleophilic Chromium(V) Dioxo Radical Anion

Treatment of Cr(NRAr)3 (R = C(CD3)2CH3 or tert-butyl, Ar = 2,5-C6H3FMe) with oxygen gives the purple
chromium(VI) complex O2Cr(NRAr)2 in 83% purified yield. Upon one-electron reduction with cobaltocene, the
d1 dioxo cobaltocenium salt [CoCp2][O2Cr(NRAr)2] was isolated in 89% yield. The dioxo anion displays solid-state magnetic behavior consistent with a Curie−Weiss paramagnet with one unpaired electron. The chromium(V) dioxo [CoCp2][O2Cr(NRAr)2] acts as a nucleophile toward ClSiPh3, ClC(O)Ph, and MeOTf to afford the
monooxo complexes OCr(OSiPh3)(NRAr)2 (86% yield), OCr[OC(O)Ph](NRAr)2 (34% yield), and OCr(OMe)(NRAr)2 (76% yield), respectively. Two of these rare examples of monooxo chromium(V) derivatives, OCr(OSiPh3)(NRAr)2 and OCr[OC(O)Ph](NRAr)2, were structurally characterized and display Cr−Ooxo distances of
1.611(6) and 1.588(3) Å, respectively. The benzoate complex features an η1-carboxylate ligand. All of the monooxo
complexes show three peaks in their 2H NMR spectra consistent with isomers arising from restricted rotation
about the Cr−N bonds. Two of the complexes, O2Cr(NRAr)2 and OCr(OSiPh3)(NRAr)2, were examined by cyclic
voltammetry.