Room-temperature stable diazoolefins provide access to a unique class of carbon-donor ligands: N-heterocyclic vinylidenes. ^[1] Herein, we describe Cp*M complexes with the N-heterocyclic vinylidene ligand IPrC (IPr = 1,3-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene). Cationic complexes of type [Cp*IrCl(IPrC)]X (X = SbF₆, OTf) were obtained by reaction of (Cp*IrCl₂)₂ with IPrCN₂, followed by chloride abstraction. Two-electron reduction instead of chloride abstraction gave a neutral Cp*Ir(IPrC) complex with a “pogo stick” geometry.^[2] Single-electron reduction of the cationic complexes afforded Cp*IrCl(IPrC), in which the vinylidene ligand shows radical character. Combining (Cp*RuCl₂)₂ with IPrCN₂ gave Cp*RuCl₂(IPrC), in which the vinylidene ligand also shows radical character. Hydrogen abstraction from Et₃SiH yielded the carbene complex Cp*RuCl₂(IPrCH). The diamagnetic complex Cp*RuCl(IPrC) was obtained by single-electron reduction of Cp*RuCl₂(IPrC), whereas single-electron oxidation with [TEMPO]X provided ionic [Cp*RuCl₂(IPrC)]X (X = BF₄, SbF₆) complexes. Reactions of  (Cp*OsBr₂)₂  with IPrCN₂ resulted in disproportionation and formed Cp*OsBr(IPrC) and [Cp*OsBr₂(IPrC)]Br, while single electron reduction of [Cp*OsBr₂(IPrC)]Br formed the meta-stable Cp*OsBr₂(IPrC) and the vinylidene ligand also shows radical character.^[3] The results underline the unique electronic properties of the vinylidene ligand IPrC in transition metal complexes. 

[1] B. Kooij, T. H. Wong, K. Severin.  Chemia., 2025, 79, 855-858

[2] T. H. Wong, P. Varava, F. Faraei-Tirani, R. Scopelliti, K. Severin.  J. Am. Chem. Soc., 2025, 147, 19911-19917.

[3] T. H. Wong, A. Sienkiewicz, F. Faraei-Tirani, R. Scopelliti, K. Severin. Manuscript in preparation.