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 CoII diketimide complex [(Tr L)Co(NC6 F5 )]2 and its reversible C-C bond cleavage to yield a monomeric Co nitrenoid complex (Tr L)Co(NC6 F5 ). Exposure of [(Tr L)Co(NC6 F5 )]2 to an excess amount of an H-atom donor cleanly affords the CoII anilide complex (Tr L)Co(NHC6 F5 ). The half-order decay of [(Tr L)Co(NC6 F5 )]2 via H-atom abstraction (HAA) reveals saturation kinetic behavior indicating a pre-equilibrium between [(Tr L)Co(NC6 F5 )]2 and (Tr L)Co(NC6 F5 ) prior to HAA. Furthermore, (Tr L)Co(NC6 F5 ) undergoes reductive coupling with another equivalent of azide to furnish the four-coordinate tetrazido complex (Tr L)Co(κ2 -N4 (C6 F5 )2 ), expulsion of a fluorine atom to afford (Tr L)CoF, and N-group transfer reactivity to PPh3 .