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

Abstract

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 ^14/15 N 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.

Keywords: N ligands; ab-initio calculations; high oxidation states; matrix isolation; transition metals.