Low-valent iron mono-diazadiene compounds: electronic structure and catalytic application

A series of monodiazadiene diolefin iron compounds, [Fe(trop(2)dad)(L)] (4; L = neutral ligand), has been prepared by one-electron oxidation of the Fe-I species [NaFe-(trop(2)dad)(thf)(3)] (dad = diazadiene; trop = 5H-dibenzo[a,d]-cyclohepten-5-yl). The electronic structures of compounds 4 were investigated by NMR and Mossbauer spectroscopy, single-crystal X-ray diffraction, solid- and liquid-phase magnetic susceptibility measurements, and DFT calculations. Compounds of type 4 with labile ligands L were found to be active (pre)catalysts for the dehydrogenative coupling of (alkyl)amine-boranes. Remarkably high activities were observed, especially for the homogeneous dehydrogenative polymerization of methylamine-borane.