High‐Spin Imido Cobalt Complexes with Imidyl Radical Character**

Abstract

We report on the synthesis of a variety of trigonal imido cobalt complexes [Co(NAryl)L 2 ] À , (L= N-(Dipp)SiMe 3 ), Dipp = 2,6-diisopropylphenyl) with very long CoÀN Aryl bonds of around 1.75 . Their electronic structure was interrogated using a variety of physical and spectroscopic methods such as EPR or X-Ray absorption spectroscopy which leads to their description as highly unusual imidyl cobalt complexes. Computational analyses corroborate these findings and further reveal that the high-spin state is responsible for the imidyl character. Exchange of the Dipp substituent on the imide by the smaller mesityl function (2,4,6-trimethylphenyl) effectuates the unexpected Me 3 Si shift from the ancillary ligand set to the imidyl nitrogen, revealing a highly reactive, nucleophilic character of the imidyl unit.

On the Synthesis of a T‐Shaped Imido Nickel Complex and Trigonal Amido Nickel Complexes

“…This can be explained by formation of the putative phenyl imido complex [ Ni(NPh)L 2 ] − (Scheme 1) with a nucleophilic imide function that then facilitates the SiMe 3 shift. This unusual phenomenon was already observed indirectly by us in case of cobalt, whereas the respective rearranged imido complex corresponding to [ 1 ] − proved to be too reactive for identification due to intramolecular C−H bond activation [36] . The formation of [ 1 ] − thus corroborates in hindsight that the SiMe 3 shift precedes C−H activation.…”

“…This unusual phenomenon was already observed indirectly by us in case of cobalt, whereas the respective rearranged imido complex corresponding to [1] À proved to be too reactive for identification due to intramolecular CÀ H bond activation. [36] The formation of [1] À thus corroborates in hindsight that the SiMe 3 shift precedes CÀ H activation. In solid state the Ni1À N1 bond length of [1] À amounts to 1.702(2) Å with a Ni1À N1À C1 bond angle of 164.8(2)°.…”

“…Examination of the reactivity of [1] showed that it is incapable of nitrene transfer to electron rich substrates (tricyclohexyl phosphine, styrene and phenyl isocyanate), an already observed behavior of related imido cobalt silylamido complexes. [17,36] Further, only a low H atom abstraction (HAA) capability is observed as exemplified by using 1,4-cyclohexadiene (CHD) as substrate. In the presented case we tentatively attribute it to the low-spin state of the nickel imide, given the otherwise fairly accessible imide function.…”

“…[17] The related high-spin arylimido cobalt complex [Co(NDipp)L 2 ] (L=À N(Dipp)SiMe 3 , Dipp = 2,6-diisopropylphenyl) exhibited radical imidyl character of the imide ligand, whereas steric protection was needed to allow for its isolation. [36] We were thus curious if these findings would translate to the heavier neighbor nickel, where a more covalent, thus more reactive metal-imide bond might be expected. [18,19]…”

High‐Spin‐Imidocobaltkomplexe mit Imidylradikalcharakter**

“…Abbildung 2. Molekülstruktur von K{18c6}[2] (links) und K[2] (rechts) im Festkçrper [58]. Das K{18c6}-Kation, Lçsungsmittelmoleküle sowie Wasserstoffatome wurden weggelassen.…”