Reversible C-C Bond Cleavage of a Cobalt Diketimide into an Elusive Cobalt Aryl Nitrenoid Complex.

The reactivity of ( ^Tr L)Co ( ^Tr L=5-mesityl-1,9-(trityl)dipyrrin) toward various aryl azides was examined to elucidate the electronic structure and reactivity of dipyrrinato cobalt aryl nitrenoid complexes. Herein, we demonstrate the synthesis of a Co ^II diketimide complex [( ^Tr L)Co(NC ₆ F ₅ )] ₂ and its reversible C-C bond cleavage to yield a monomeric Co nitrenoid complex ( ^Tr L)Co(NC ₆ F ₅ ). Exposure of [( ^Tr L)Co(NC ₆ F ₅ )] ₂ to an excess amount of an H-atom donor cleanly affords the Co ^II anilide complex ( ^Tr L)Co(NHC ₆ F ₅ ). The half-order decay of [( ^Tr L)Co(NC ₆ F ₅ )] ₂ via H-atom abstraction (HAA) reveals saturation kinetic behavior indicating a pre-equilibrium between [( ^Tr L)Co(NC ₆ F ₅ )] ₂ and ( ^Tr L)Co(NC ₆ F ₅ ) prior to HAA. Furthermore, ( ^Tr L)Co(NC ₆ F ₅ ) undergoes reductive coupling with another equivalent of azide to furnish the four-coordinate tetrazido complex ( ^Tr L)Co(κ ² -N ₄ (C ₆ F ₅ ) ₂ ), expulsion of a fluorine atom to afford ( ^Tr L)CoF, and N-group transfer reactivity to PPh ₃ .
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