A Pair of Cobalt(III/IV) Terminal Imido Complexes
Weiqing Mao, Dominik Fehn, Frank W. Heinemann, Andreas Scheurer, Dominik Munz, Karsten Meyer
Abstract
Abstract The 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‐adamantylazide yields the cobalt(III) imido complex [(TIMMN mes )Co III (NAd)](BPh 4 ) ( 3 ) with concomitant release of dinitrogen. The N‐anchor in diamagnetic 3 features an unusual, planar tertiary amine, which results from repulsive electrostatic interaction with the filled d(z 2 )‐orbital of the cobalt ion 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 ). Despite a half‐life of less than 1 h at room temperature, 4 could be isolated at low temperatures in analytically pure form. Single‐crystal X‐ray diffractometry and EPR spectroscopy corroborate the molecular structure and the d 5 low‐spin, S= , electron configuration. A computational 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.