The use of O-atom transfer agents to generate high valent, metal-oxo species has created an interest in the mechanism of their reactions. Traditionally, the O-atom transfer agent, such as iodosylbenzene, performs a two-electron oxidation with the transfer of oxygen to a metal center. In transition metal catalyzed oxidation reactions employing iodosylbenzene, the metal-oxo species is a commonly invoked intermediate, though its formation is not always demonstrated. Recently, the isolation of transition metal adducts of O-atom transfer agents has brought into light the potential for the involvement of such adducts in oxidation reactions rather than the putative metal-oxo intermediate. Herein is presented the first example of a crystallographically characterized Co(II)-iodosylarene complex supported by the bulky, hydrotris(3-adamantyl-5-methylpyrazolyl)borate ligand (TpAd,Me). Bond metrics indicate the oxidation state of Co and the iodosylarene ligand itself appear unchanged upon formation of the adduct. The Co(II)-iodosylarene adduct is remarkably stable, decaying with an observed rate of 1.3 (±0.3) x 10-5 s-1 at room temperature in diethyl ether. The stability is proposed to be a reflection of the poor electronic donation from the ligand, preventing I-O bond scission, in addition to steric protection provided by the bulky adamantyl substituents, preventing solvent access to the bound oxygen atom. In turn, the complex displays poor O-atom transfer reactivity to substrates; reacting with phosphines to generate phosphine oxides but unreactive towards thioethers or alkenes. The suppressed reactivity is attributed to the steric protection provided by the TpAd,Me ligand. Additional physical and chemical properties of the complex will also be presented.

Synthesis and characterization of a Co(II)-iodosylarene adduct

255th National Meeting (2018)

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