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 [(TIMMNmes)Co-I](PF6) (TIMMNmes = tris-[2-(3-mesityl-imidazolin-2-ylidene)-methyl]amine) with p-methoxyphenyl azide yields a Co-III imide [(TIMMNmes)Co-III(NAnisole)](PF6) (1). Treatment of 1 with 1 equiv of [FeCp2](PF6) at -35 degrees 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 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 CoIII with significant Co-IV imidyl radical character. Verifying the pronounced electrophilicity, nucleophiles such as H2O and (BuNH2)-Bu-t add to 3-analogous to the parent free nitrene-in the para position of the aromatic substituent, thus, clearly corroborating singlet nitrene-type reactivity.

Automated summary

This study describes the synthesis, characterization, and reactivity of a series of cobalt terminal imido complexes supported by an N-anchored tripodal tris(carbene) chelate. The complexes were fully characterized using various spectroscopic and crystallographic techniques. Quantum chemical calculations provided insight into the electronic structures of the compounds. The findings highlight the reactivity of these cobalt imido complexes, including their ability to undergo intramolecular C-H bond amination and nucleophilic addition reactions.