Synthesis, Characterization, and Alkyne Trimerization Catalysis of a Heteroleptic Two-Coordinate Fe<sup>I</sup> Complex

The synthesis of the first heteroleptic, two-coordinate Fe<sup>I</sup> complex IPr–Fe–N­(SiMe<sub>3</sub>)­DIPP (<b>1</b>) (IPr = 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene; DIPP = 2,6-<sup><i>i</i></sup>Pr<sub>2</sub>–C<sub>6</sub>H<sub>3</sub>) is reported. Protonation of the Fe<sup>II</sup> bis­(amido) complex Fe­[N­(SiMe<sub>3</sub>)­DIPP]<sub>2</sub> followed by addition of IPr and reduction by potassium graphite in a one-pot reaction results in good yields of <b>1</b>. The redox activity of <b>1</b> and comparison between <b>1</b> and its reduction product by <sup>57</sup>Fe Mössbauer spectroscopy are discussed, and the reduction was found to be metal-based rather than ligand-based. The activity of <b>1</b> toward the catalytic cyclotrimerization of terminal and internal alkynes is described.