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

Abstract

The reactivity of (L-Tr)Co (L-Tr=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 [(L-Tr)Co(NC6F5)](2) and its reversible C-C bond cleavage to yield a monomeric Co nitrenoid complex (L-Tr)Co(NC6F5). Exposure of [(L-Tr)Co(NC6F5)](2) to an excess amount of an H-atom donor cleanly affords the Co-II anilide complex (L-Tr)Co(NHC6F5). The half-order decay of [(L-Tr)Co(NC6F5)](2) via H-atom abstraction (HAA) reveals saturation kinetic behavior indicating a pre-equilibrium between [(L-Tr)Co(NC6F5)](2) and (L-Tr)Co(NC6F5) prior to HAA. Furthermore, (L-Tr)Co(NC6F5) undergoes reductive coupling with another equivalent of azide to furnish the four-coordinate tetrazido complex (L-Tr)Co(kappa(2)-N-4(C6F5)(2)), expulsion of a fluorine atom to afford (L-Tr)CoF, and N-group transfer reactivity to PPh3.