A Pair of Cobalt(III/IV) Terminal Imido Complexes.

2021 
Reaction of the cobalt(I) complex [(TIMMN mes )Co I ](BPh 4 ) ( 2 ) (TIMMN mes = t ris -[2-(3-mesityl- im idazolin-2-ylidene)- m ethyl]-ami n e) with 1-adamantyl azide yields the cobalt(III) imido complex [(TIMMN mes )Co III (NAd)](BPh 4 ) ( 3 ) with concomitant release of dinitro-gen. The N -anchor in diamagnetic 3 features an unusual, planar tertiary amine, which results from repulsive electro-static interaction with the cobalt ion's filled d ( z 2 ) orbital and negative hyperconjugation with the neighboring methylene groups. One-electron oxidation of 3 with [FeCp 2 ][OTf] provides access to the rare, high valent cobalt(IV) imido complex [(TIMMN mes )Co IV -(NAd)](OTf) 2 ( 4 ). Both complexes 3 and 4 were fully characterized. Despite a half-life of less than one hour at room temperature, 4 could be isolated at low temperatures in analytically pure form. Single-crystal X-ray diffractometry (SC-XRD) and EPR spectroscopy corroborate the compound's molecular structure and its d 5 low-spin, S = ½, electron configuration. A compu-tational analysis of 4 suggests high covalency within the Co IV =NAd bond with non-negligible spin density located at the imido moiety, which translates into substantial triplet nitrene character.
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