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

Abstract

The fluoronitrenoid metal complexes FNCoF 2 and FNRhF 2 as well as the first ternary Rh VI and Ir VI complexes NIrF 3 and NRhF 3 are described. They were obtained by the reaction of excited Group-9 metal atoms with NF 3 and their IR spectra, isolated in solid rare gases (neon and argon), were recorded. Aided by the observed 14/15 Ni sotope shifts and quantum-chemical predictions,a ll four stretching fundamentals of the novel complexes were safely assigned. The F À N stretching frequencies of the fluoronitrenoid complexes FNCoF 2 (1056.8 cm À1)a nd FNRhF 2 (872.6 cm À1)a re very different and their NÀMb onds vary greatly.I nF NCoF 2 ,t he FN ligand is singly bonded to Co and bears considerable iminyl/nitrene radical character,w hile the N À Rh bond in FNRhF 2 is astrong double bond with comparatively strong sand p-bonds.The anticipated rearrangement of FNCoF 2 to the nitrido Co VI complex is predicted to be endothermic and was not observed.

High‐Spin Imido Cobalt Complexes with Imidyl Radical Character**

“…This is increasingly employed for the catalytic amination of unfunctionalized C−H bonds or the aziridation of olefines. [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 ] Despite the resulting high demand for understanding late 3d‐transition metal imido species, comprehensive knowledge about the electronic and structural factors that contribute to their properties and bond activation reactivity is still lacking. Whereas most isolable imido metal complexes are found in a low‐spin state, those with higher spin‐states tend to be more reactive.…”

High‐Spin Iron(VI), Low‐Spin Ruthenium(VI), and Magnetically Bistable Osmium(VI) in Molecular Group 8 Nitrido Trifluorides NMF3

“…For the d 0 configurations of all group 4 and group 6 nitrido trifluorides the ideal pseudo‐tetrahedral C 3v symmetric arrangement was experimentally verified, since there are no electrons in the nonbonding e (d xy , x 2− y 2 ) orbitals that could cause distortions [25,33] . The e 3 configuration of NRhF 3 and NIrF 3 leads to Jahn−Teller distorted spin doublet ground states in C s symmetry [26] . So far, no experimental data are available for the group 10 derivatives, and for the group 11 analogues only the initial metal insertion products F 2 N−M II F were detected after matrix deposition (irradiation of F 2 NCuF led to rearrangement to metastable FN=CuF 2 ) [30c] …”

“…However, the very strong NF 3 precursor bands and comparatively weak NF and NF 2 bands in all spectra suggest that the formation of the NMF 3 title product can be attributed to the reaction of M and NF 3 . Lower nitrido fluorides NMF or NMF 2 could in principle also be formed through the cleavage of a metal‐fluorine bond or by the reaction of metal atoms with NF or NF 2 , but have so far not been identified [25,26,30c,33] . The addition of fluorine to NMF and NMF 2 to yield NMF 3 and also the formation of NMF 4 for M=Ru and Os are calculated to be exothermic (Table S2).…”

“…[c] Ne matrix (this work). [d] Ne and Ar matrices [26] . [e] Formation of N≡RhF 3 along with FN=RhF 2 .…”

“…In the series of 3d NM VI F 3 compounds, for M=Fe it seems we have reached the limit of stability. NCo VI F 3 is not a stable compound and only FNCoF 2 has been observed experimentally [26] . For the 4 d element Rh it was found that the rearrangement of the fluoro nitrene complex FNRhF 2 into N≡Rh VI F 3 is only slightly exothermic (Δ H 0 =−12 kJ mol −1 , CCSD(T)), which enables the observation of both rearrangement products [26] …”