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

• Published in: Journal of organometallic chemistry 2020-09, Vol.923, p.121436, Article 121436
• Main Authors: Taniguchi, Wakano, Ito, Jun-ichi, Yamashita, Makoto
• Format: Article
• Language: English
• Subjects: Alkene hydrogenation; DFT calculations; Iron; N-Heterocyclic carbene; Pincer complexes
• ISSN: 0022-328X; 1872-8561
• DOI: 10.1016/j.jorganchem.2020.121436

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)H3]2+[I−]2 (1a) 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)H3]2+[I−]2 (1b) 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. •CNC-pincer Fe complexes containing a bis(NHC)amido ligand were synthesized and characterized by X-ray diffraction study.•CNC-pincer Fe complexes were found to be active in hydrogenation of alkenes.•DFT calculations suggested the monohydride mechanism on the triplet surface.