From Ylides to Doubly Yldiide-Bridged Iron(II) High Spin Dimers via Self-Protolysis.

A synthetic strategy for the preparation of novel doubly yldiide bridged iron(II) high spin dimers ([(μ-C)FeL], L = N(SiMe), Mesityl) has been developed. This includes the synthesis of ylide-iron(II) monomers [(Ylide)FeL] via adduct formation. Subsequent self-protolysis at elevated temperatures by deprotonation of the ylide ligands results in a dimerization reaction forming the desired bridging μ-C yldiide ligands in [(μ-C)FeL]. The comprehensive structural and electronic analysis of dimers [(μ-C)FeL], including NMR, Mössbauer, and X-ray spectroscopy, as well as X-ray crystallography, SQUID, and DFT calculations, confirm their high-spin Fe configurations. Interestingly, the FeC cores display very acute Fe-C-Fe angles (averaged: 78.6(2)°) resulting in short Fe···Fe distances (averaged: 2.588(2) Å). A remarkably strong antiferromagnetic coupling between the Fe centers has been identified. Strongly polarized Fe-C bonds are observed where the negative charge is mostly centered at the μ-C yldiide ligands.