Toward understanding highly electron-withdrawing terminal Fe(IV) imides

Terminal iron imido complexes with highly electron-withdrawing N-substituents have remained elusive despite their proposed implication in N-group-transfer chemistry. In a recent issue of Cell Reports Physical Science, Deng and co-workers report the isolation characterization an N-trifluoromethyl-substituted Fe(IV) bis-imido species that displays triplet ground state undergoes intramolecular C‒H activation. bond amination via methods has been widely explored as means to introduce functionality into unreactive bonds without need for substrate pre-oxidation.1Park Y. Kim Chang S. Transition metal-catalyzed C–H amination: scope, mechanism, applications.Chem. Rev. 2017; 117: 9247-9301Crossref PubMed Scopus (1296) Google Scholar The array N-transfer reagents available transition-metal developed thus enabled diverse reactivity, dictated by nature interaction between metal nitrene fragment.2Gephart R.T. Warren T.H. Copper-catalyzed sp3 amination.Organometallics. 2012; 31: 7728-7752Crossref (263) this context, (M‒NR) implicated numerous functionalization processes, reactivity trends extensively studied. Factors such spin oxidation state, ligand identity, metal-imido geometry, electronic profile (e.g., alkyl versus aryl or electron poor rich) shown influence M‒NR unit.3Wilding M.J.T. Iovan D.A. Betley T.A. High-spin competent amination.J. Am. Chem. Soc. 139: 12043-12049Crossref (79) Scholar, 4Wilding Wrobel A.T. Lukens J.T. MacMillan S.N. Lancaster K.M. Direct comparison efficacy through manipulation nitrogen-valence centered redox: iminyl.J. 14757-14766Crossref (76) 5Baek Hennessy E.T. geometry: key principles enhance efficacy.J. 2019; 141: 16944-16953Crossref (28) 6Anneser M.R. Elpitiya G.R. Townsend J. Johnson E.J. Powers X.B. DeJesus J.F. Vogiatzis K.D. Jenkins D.M. Unprecedented five-coordinate iron(IV) imides generate divergent states based on imide R-groups.Angew. Int. Ed. 58: 8115-8118Crossref (24) Of note, N-tosyliminophenyliodinane, 3,5-bis-trifluoromethylphenyl azide, p-nitrophenyl azide) tend consistently display enhanced both olefin aziridination transformations various catalysts.2Gephart Scholar,7Intrieri D. Caselli A. Ragaini F. Macchi P. Casati N. Gallo E. Insights mechanism ruthenium-porphyrin-catalysed allylic olefins azides.Eur. Inorg. : 569-580Crossref (38) Scholar,8Wang L. Recent advances iron-catalyzed C-H intermediate.Chin. 2018; 36: 1222-1240Crossref (66) Within prolific research area, catalysts attracted significant interest because sustainable alternative distinct they offer second- third-row congeners. As such, prepared characterized;8Wang yet, terminal bearing eluded crystallographic characterization. Given is often promoted electrophilic metal-ligand multiple-bond moieties, electron-poor fragment most likely contributes character Fe‒NR unit. However, changes overall structure imide, example, cannot be excluded, emphasizing further studies aid elucidating structure-reactivity relationships governing processes. To end, Science first terminally bound complex decorated bis-trifluoromethyl substituents.9Liu Q. Long Ma Leng X. Xiao Chen H. Synthesis, structure, activation reaction trifluoromethyl groups.Cell Rep. Phys. Sci. 2021; 2: 100454https://doi.org/10.1016/j.xcrp.2021.100454Abstract Full Text PDF (3) A long Fe‒N bonds, bent Fe‒N‒C angle describe unique features bis-imide compared its non-fluorinated analog contribute observed hydrogen atom abstraction (HAA) reactivity. These findings provide, time, direct electronically complementary (i.e., electron-rich methyl groups) species, offering insight impact substituents authors build upon previous carbene-supported Fe(0) synthons able access Fe( IV ) using more mesityl 2,6-diisopropyl) substituents.10Wang Hu Zhang Three-coordinate bisimido aminocarbene ligation: synthesis, reactivity.J. 2015; 137: 14196-14207Crossref (64) Following similar protocol, [(IPr)Fe(dvtms)] (IPr = 1,3-bis(2′,6′-diisopropylphenyl)imidazol-2-ylidene; dvtms divinyltetramethylsiloxane) either 1,1,1,3,3,3-hexaflouro-2-phenyl-2-azidopropane 2-phenyl-2-azido-propane afforded corresponding 1-CF3 (Figure 1A) 1-CH3 1B), respectively, validated X-ray crystallography.9Liu Several differences emerged from analyzing solid-state structures these two species. displayed metrics those previously isolated 2,6-diisopropylphenyl (2-Dipp; Figure 1C)10Wang short lengths (1.63 Å average), angles (average: 156.5° 1-CH39Liu 166.5° 2-Dipp10Wang Scholar), coplanar arrangement NHC imidazole ring Nimido‒Fe‒Nimido plane. Alternatively, deviations values were noted 1-CF3, which had average 1.71 Å, 142°, rotation plane away ring, forming dihedral 81.6°.9Liu noticeable crystallographically are reflected elongated acute consistent spectroscopically detected contrasting diamagnetic 1-CH3.9Liu structural perturbations, along elongation respective Fe‒Ccarbene serve (1) lower energy 3dz2 orbital involved σ interactions carbene units (2) stabilize 3dxz result diminished π-overlap Nimido 2p orbitals bending moiety. result, population enables S 1 1A), corroborated paramagnetic 1H NMR spectrum, effective magnetic moment 3.30(3) μB, 57Fe Mӧssbauer isomer shift ‒0.13 mm/s.9Liu spectroscopic properties bis-imides led profiles. HAA one isopropyl occurred readily afford new ferrous bis-amide whereas no was even at elevated temperatures. Interestingly, heating 100°C, related 2-Dipp underwent dehydrogenated substituent group itself instead supporting 1C).10Wang takeaway points can gleaned higher relative correlates propensity line low-lying excited invoked rationalize temperatures.10Wang Further, highlight parameters closely resemble computationally found identified transition (TS) initial step. perpendicular arragngement planes— computed TS only 1-CF3—is also particularly notable. Nevertheless, acknowledge increased steric demand could orientation units.9Liu newly synthesized α,α-bis(trifluoromethyl)benzyl reported co-workers9Liu represents step forward toward comprehensive understanding catalytic Spectroscopic unveiled coordination geometry resembling HAA, oxidative potency analogs. Overall, support correlation provide experimental evidence heightened substituted groupsLiu et al.Cell ScienceJune 7, 2021In BriefIron intermediates many reactions dinitrogen reduction. Liu al. CF3 groups [(IPr)Fe(NC(CF3)2Ph)], spin-state, Fe-N(imido) Fe-N(imido)-C undergo reactions. different [(IPr)Fe(NC(CH3)2Ph)]. Full-Text Open Access