Iron(II) Complexes Featuring Bidentate N‑Heterocyclic Carbene–Silyl Ligands: Synthesis and Characterization

Two silyl donor containing N-heterocyclic carbene iron­(II) complexes, [(CSi)­Fe­(IMes′)] (CSi = bidentate silyl donor containing N-heterocyclic carbene ligand, IMes′ = cyclometalated IMes ligand, IMes = 1,3-dimesitylimidazol-2-ylidene) have been synthesized by sequential iron-mediated benzylic C–H bond activation and silylation reactions starting from [(IMes)2FeCl2]. Single-crystal X-ray diffraction studies revealed that the [(CSi)­Fe­(IMes′)] complexes have seesaw-type FeSiC3 cores. Solution magnetic susceptibility measurements, UV–vis–near-IR spectra, and bond distance data from X-ray diffraction studies corroborate an intermediate spin state, S = 1, for these unique iron­(II) complexes. DFT calculations revealed that the bidentate CSi chelates are essentially σ-donating ligands in the iron­(II) compounds.