A bulky bis N-heterocyclic carbene complex of iron with coordination number of six: [CpFe(CO)(CH2(ImtBu)2)]I (where ImtBu = 3-tert-butyl-1H-imidazol-1-yl-2(3H)-ylidene)

•A new iron bis NHC complex was made, [CpFe(CH2(ImtBu)2CO]I.•This is the only octahedral complex with a bis NHC ligand this bulky.•This complex is unreactive toward CO oxidation with ONMe3, and this complex also resists CO loss by photolysis.•Treatment with hydride reagents typically leads to decomposition.•This is an interesting new complex, but it has limited use for further synthetic manipulation.

The crystal structure of the title compound, [CpFe(CO)(CH2(ImtBu)2)]I (where ImtBu = 3-tert-butyl-1H-imidazol-1-yl-2(3H)-ylidene) (1), has been studied by X-ray diffraction. A piano-stool geometry is observed with binding of the Cp ring in three coordination sites, the chelating bis N-heterocyclic carbene (NHC) ligand in two sites, and the CO ligand. This molecule is a cation and the iodide provides a counter-anion that is not coordinated. This structure is similar to other bidentate chelating NHC complexes in the literature, but the combination of t-butyl groups in a pseudo-six-coordinate complex makes the title compound more sterically crowded than its literature analogs. This complex is remarkably stable, with attempts to displace the CO ligand proving unsuccessful and leading to no reaction or decomposition under forcing conditions.

Graphical abstractA very bulky bidentate chelating N-heterocyclic carbene (NHC) complex of Fe is reported; perhaps due to the strongly donating carbene carbons and the π accepting CO ligand, this complex resists substitution of the CO ligand.Figure optionsDownload full-size imageDownload as PowerPoint slide