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

[Image: see text] A synthetic strategy for the preparation of novel doubly yldiide bridged iron(II) high spin dimers ([(μ(2)-C)FeL](2), L = N(SiMe(3))(2), Mesityl) has been developed. This includes the synthesis of ylide-iron(II) monomers [(Ylide)FeL(2)] via adduct formation. Subsequent self-protolysis at elevated temperatures by in situ deprotonation of the ylide ligands results in a dimerization reaction forming the desired bridging μ(2)-C yldiide ligands in [(μ(2)-C)FeL](2). The comprehensive structural and electronic analysis of dimers [(μ(2)-C)FeL](2), including NMR, Mössbauer, and X-ray spectroscopy, as well as X-ray crystallography, SQUID, and DFT calculations, confirm their high-spin Fe(II) configurations. Interestingly, the Fe(2)C(2) 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(2)-C yldiide ligands.