Iron and Cobalt Metallotropism in Remote-Substituted NHC Ligands: Metalation to Abnormal NHC Complexes or NHC Ring Opening

Metallotropism of the M[N(SiMe₃)₂]₂ metal fragment in the tautomeric system IA^R⇌AC^R involving imidazolium salts/N-heterocyclic carbenes with remote aminide/amine substituents, respectively, is manifested by its C_NHC carbophilicity (R=tBu, M=Co, Fe) or NR_aminido nitrogenophilicity (R=Cy, M=Co, Fe; R=Mes, M=Fe) and has been rationalized on the basis of steric and electronic effects. The thermolysis products of the [M{N(SiMe₃)₂}₂]/ IA^R⇌AC^R system are also substituent-dependent, leading to a rearranged aminide-functionalized aNHC Co₂ complex of an unprecedented type or to ring-opened metallaketenimines; they are postulated to originate from different metalloisomers. The results are interpreted on the basis of the X-ray diffraction analysis of 11 new compounds.