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 .