A Nucleophilic Chromium(V) Dioxo Radical Anion

Treatment of Cr(NRAr)(3) (R = C(CD(3))(2)CH(3) or tert-butyl, Ar = 2,5-C(6)H(3)FMe) with oxygen gives the purple chromium(VI) complex O(2)Cr(NRAr)(2) in 83% purified yield. Upon one-electron reduction with cobaltocene, the d(1) dioxo cobaltocenium salt [CoCp(2)][O(2)Cr(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 [CoCp(2)][O(2)Cr(NRAr)(2)] acts as a nucleophile toward ClSiPh(3), ClC(O)Ph, and MeOTf to afford the monooxo complexes OCr(OSiPh(3))(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(OSiPh(3))(NRAr)(2) and OCr[OC(O)Ph](NRAr)(2), were structurally characterized and display Cr-O(oxo) distances of 1.611(6) and 1.588(3) Å, respectively. The benzoate complex features an eta(1)-carboxylate ligand. All of the monooxo complexes show three peaks in their (2)H NMR spectra consistent with isomers arising from restricted rotation about the Cr-N bonds. Two of the complexes, O(2)Cr(NRAr)(2) and OCr(OSiPh(3))(NRAr)(2), were examined by cyclic voltammetry.