CNC-pincer iron complexes containing a bis(N-heterocyclic carbene) Amido ligand: Synthesis and application to catalytic hydrogenation of alkenes

This work studied preparation and catalytic application of CNC-pincer Fe complexes containing a bis(NHC)amido ligand (NHC: N-heterocyclic carbene). Deprotonation of bis(3-isopropylimidazoliumyl) amine salt [(CNCiPr)H-3](2+)[I-](2) (la) with lithium hexamethyldisilazide (LiHMDS) afforded the corresponding bis(NHC)amido-Li complex 2a. Treatment of in-situ generated 2a with FeI2(thf)(2) gave a CNC-pincer Fe(II) iodide complex Fe(CNCiPr)I (3a) and a cationic homoleptic Fe(III) complex [Fe(CNCiPr)(2)]I-+(-) (4a). Reaction of in-situ generated 2a with Fe[N(SiMe3)(2)](2) produced the corresponding amido complex Fe(CNCiPr)[N(SiMe3)(2)] (5a). Similarly, deprotonation of a less hindered methyl analogue [(CNCMe)H-3](2)(+)[I-](2) (lb) with LiHMDS followed by treatment of Fe[N(SiMe3)(2)](2) gave an amido complex Fe(CNCMe) [N(SiMe3)(2)] (5b). Molecular structures of 3a, 5a and 5b, which were confirmed by X-ray diffraction study, showed a distorted tetrahedral geometry. Complexes 3a and 5b were found to be active in hydrogenation of alkenes. Reaction mechanism was investigated by density functional theory (DFT) calculations. (C) 2020 Elsevier B.V. All rights reserved.