Fluoro Nitrenoid Complexes FN=MF2 (M=Co,Rh, Ir): Electronic Structure Dichotomy and Formation of Nitrido Fluorides N≡MF3

The fluoronitrenoid metal complexes FNCoF₂ and FNRhF₂ as well as the first ternary Rh^VI and Ir^VI complexes NIrF₃ and NRhF₃ are described. They were obtained by the reaction of excited Group-9 metal atoms with NF₃ and their IR spectra, isolated in solid rare gases (neon and argon), were recorded. Aided by the observed ^14/15N isotope shifts and quantum-chemical predictions, all four stretching fundamentals of the novel complexes were safely assigned. The F−N stretching frequencies of the fluoronitrenoid complexes FNCoF₂ (1056.8 cm⁻¹) and FNRhF₂ (872.6 cm⁻¹) are very different and their N−M bonds vary greatly. In FNCoF₂, the FN ligand is singly bonded to Co and bears considerable iminyl/nitrene radical character, while the N−Rh bond in FNRhF₂ is a strong double bond with comparatively strong σ- and π-bonds. The anticipated rearrangement of FNCoF₂ to the nitrido Co^VI complex is predicted to be endothermic and was not observed.