Abstract
The fluoronitrenoid metal complexes FNCoF2 and FNRhF2 as well as the first ternary RhVI and IrVI 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 CoVI complex is predicted to be endothermic and was not observed.
Highlights
Fluoronitrenoid metal complexes are underexplored compounds as only two examples have been reported so far, FNReF5 and FNCuF2.[2]
The imido ligands in late 3d transition metal complexes are often so electrophilic that these complexes can be better described as metal-nitrene complexes (Scheme 1)
Complementary argon spectra for the experiments using rhodium and iridium have been recorded and shown in the supporting information, Figures S1–S3. These spectra are dominated by strong bands of the NF3 precursor (Figure S4, Table S2 and Ref. [17]) and its plasma radiation induced decomposition products NF and NF2.[18] the assignment of IR bands associated with the targeted nitrene and nitrido complexes is facilitated by a characteristic 14/15N isotope shift exhibited by all modes in which the nitrogen atom is significantly involved
Summary
Fluoronitrenoid metal complexes are underexplored compounds as only two examples have been reported so far, FNReF5 and FNCuF2.[2]. Such high-valent group 9 metals are still unknown They would be of particular interest for cobalt, since the highest oxidation state reported for any molecular complex of cobalt is V, for example, the well-known [Co(1-norbornyl)4]+ or in the tricoordinated cationic bis(nitrene) cobalt complex [(IMes)Co(NDipp)2]+.[6,14] The latter low-coordinated cationic complex is supported by the strongly electron-donating and sterically demanding N-heterocyclic carbene ligand IMes, and has been obtained by oxidation of the corresponding neutral bis(nitrene) CoIV complex. Theoretical calculations indicated that the frontier molecular orbitals of these bis(nitrene) complexes have near-equal contributions from both the cobalt center and the nitrene ligand orbitals, indicating that the spectroscopic oxidation states for these cobalt centers are likely to be lower than IV and V, respectively Apart from these bis(nitrene) complexes, the majority of the known cobalt nitrenoid complexes have low spin CoIII centers which are supported, for example, by bulky ancillary tripodal or bidentate ligands to achieve kinetic stabilization.[15] To the contrary, terminal nitrido complexes of cobalt still remain elusive.[16]
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