A Comprehensive Analysis of the Metal-Nitrile Bonding in an Organo-Diiron System.

Nitriles (N≡CR) are ubiquitous in coordination chemistry, yet literature studies on metal-nitrile bonding based on a multi-technique approach are rare. We selected an easily-available di-organoiron framework, containing both π-acceptor (CO, aminocarbyne) and donor (Cp = η5 -C5 H5 ) ligands, as a suitable system to provide a comprehensive description of the iron-nitrile bond. Thus, the new nitrile (2-12)CF3 SO3 and the related imine/amine complexes (8-9)CF3 SO3 were synthesized in 58-83% yields from the respective tris-carbonyl precursors (1a-d)CF3 SO3 , using the TMNO strategy (TMNO = trimethylamine-N-oxide). The products were fully characterized by elemental analysis, IR (solution and solid state) and multinuclear NMR spectroscopy. In addition, the structures of (2)CF3 SO3 , (3)CF3 SO3 , (5)CF3 SO3 and (11)CF3 SO3 were ascertained by single crystal X-ray diffraction. Salient spectroscopic data of the nitrile complexes are coherent with the scale of electron-donor power of the R substituents; otherwise, this scale does not match the degree of Fe → N π-back-donation and the Fe-N bond energies, which were elucidated in (2-7)CF3 SO3 by DFT calculations.