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 diorganoiron framework, containing both π-acceptor (CO, aminocarbyne) and donor (Cp = η5−C5H5 ) ligands, as a suitable system to provide a comprehensive description of the iron–nitrile bond. Thus, the new nitrile (2–12)CF3SO3 and the related imine/amine complexes (8–9)CF3SO3 were synthesized in 58–83% yields from the respective tris-carbonyl precursors (1a–d)CF3SO3, 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)CF3SO3, (3)CF3SO3, (5)CF3SO3 and (11)CF3SO3 were ascertained by single crystal X-ray diffraction. Salient spectroscopic data of the nitrile complexes are coherent with the scale of electrondonor power of the R substituents; otherwise, this scale does not match the degree of Fe → N π-backdonation and the Fe–N bond energies, which were elucidated in (2–7)CF3SO3 by DFT calculations.