Synthesis and Reactivity of a Cobalt-Supported Singlet Nitrene.

The synthesis, characterization, and reactivity of a series of cobalt terminal imido complexes supported by an N -anchored tripodal tris(carbene) chelate is described, including a Co-supported singlet nitrene. Reaction of the Co I precursor [(TIMMN mes )Co I ](PF 6 ) (TIMMN mes = t ris -[2-(3-mesityl- im idazolin-2-ylidene)- m ethyl]ami n e) with p -methoxyphenyl azide yields a Co III imide [(TIMMN mes )Co III (NAnisole)](PF 6 ) ( 1 ). Treatment of 1 with 1 equiv of [FeCp 2 ](PF 6 ) at -35 °C affords a formal Co IV imido complex [(TIMMN mes )Co(NAnisole)](PF 6 ) 2 ( 2 ), which features a bent Co-N(imido)-C(Anisole) linkage. Subsequent one-electron oxidation of 2 with 1 equiv of AgPF 6 provides access to the tricationic cobalt imido complex [(TIMMN mes )Co(NAnisole)](PF 6 ) 3 ( 3 ). All complexes were fully characterized, including single-crystal X-ray diffraction (SC-XRD) analyses, infrared (IR) vibrational, ultraviolet/visible (UV/vis) electronic absorption, multinuclear NMR, X-band electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR), and high-energy-resolution fluorescence-detected X-ray absorption spectroscopy (HERFD XAS). Quantum chemical calculations provide additional insight into the electronic structures of all compounds. The dicationic Co IV imido complex 2 exhibits a doublet ground state with considerable imidyl character as a result of covalent Co-NAnisole bonding. At room temperature, 2 readily converts to a Co II amine complex involving intramolecular C-H bond amination. Electronically, tricationic complex 3 can be understood as a singlet nitrene bound to Co III with significant Co IV imidyl radical character. Verifying the pronounced electrophilicity, nucleophiles such as H 2 O and t BuNH 2 add to 3 ─analogous to the parent free nitrene─in the para position of the aromatic substituent, thus, clearly corroborating singlet nitrene-type reactivity.