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 CoI precursor [(TIMMNmes)­CoI]­(PF6) (TIMMNmes = tris-[2-(3-mesityl-imidazolin-2-ylidene)-methyl]­amine) with p-methoxyphenyl azide yields a CoIII imide [(TIMMNmes)­CoIII(NAnisole)]­(PF6) (1). Treatment of 1 with 1 equiv of [FeCp2]­(PF6) at −35 °C affords a formal CoIV imido complex [(TIMMNmes)­Co­(NAnisole)]­(PF6)2 (2), which features a bent Co–N­(imido)–C­(Anisole) linkage. Subsequent one-electron oxidation of 2 with 1 equiv of AgPF6 provides access to the tricationic cobalt imido complex [(TIMMNmes)­Co­(NAnisole)]­(PF6)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 CoIV 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 CoII amine complex involving intramolecular C–H bond amination. Electronically, tricationic complex 3 can be understood as a singlet nitrene bound to CoIII with significant CoIV imidyl radical character. Verifying the pronounced electrophilicity, nucleophiles such as H2O and t BuNH2 add to 3analogous to the parent free nitrenein the para position of the aromatic substituent, thus, clearly corroborating singlet nitrene-type reactivity.