The combined use of aminocarbene and divinyltetramethyldisiloxane (dvtms) as supporting ligands enables the access of unprecedented low-coordinate iron(0) alkene compounds [L(n)Fe(η(2):η(2)-dvtms)] (L=N-heterocyclic carbene (NHC) or cyclic (alkyl)(amino)carbene (CAAC), n=1 or 2) from the reactions of FeCl2 with alkali-metal reducing agents, free aminocarbene ligands, and dvtms. The iron(0) species deliver their {L(n)Fe(0)} fragments to perform redox reactions with Ph2SiH2, S8, Se, and DippN3, furnishing novel aminocarbene-supported iron(IV) silylene, all-ferrous iron-sulfur/selenium cubanes, and bis(imido)iron(IV) compounds. These conversions demonstrate the potential synthetic utility of the carbene-supported iron(0) complexes as a valuable class of low-coordinate iron(0) reagents.

High-valent iron imido species are implicated as reactive intermediates in many iron-catalyzed transformations. However, isolable complexes of this type are rare, and their reactivity is poorly understood. Herein, we report the synthesis, characterization, and reactivity studies on novel three-coordinate iron(IV) bisimido complexes with aminocarbene ligation. Using our recently reported synthetic method for [LFe(NDipp)2] (L = IMes, 1; Me2-cAAC, 2), four new iron(IV) imido complexes, [(IPr)Fe(NDipp)2] (3) and [(Me2-cAAC)Fe(NR)2] (R = Mes, 4; Ad, 5; CMe2CH2Ph, 6), were prepared from the reactions of three-coordinate iron(0) compounds with organic azides. Characterization data acquired from (1)H and (13)C NMR spectroscopy, (57)Fe Mössbauer spectroscopy, and X-ray diffraction studies suggest a low-spin singlet ground state for these iron(IV) complexes and the multiple-bond character of their Fe-N bonds. A reactivity study taking the reactions of 1 as representative revealed an intramolecular alkane dehydrogenation of 1 to produce the iron(II) complex [(IMes)Fe(NHDipp)(NHC6H3-2-Pr(i)-6-CMe═CH2)] (7), a Si-H bond activation reaction of 1 with PhSiH3 to produce the iron(II) complex [(IMes)Fe(NHDipp)(NDippSiPhH2)] (8), and a [2+2]-addition reaction of 1 with PhNCNPh and p-Pr(i)C6H4NCO to form the corresponding open-shell formal iron(IV) monoimido complexes [(IMes)Fe(NDipp)(N(Dipp)C(NPh)(═NPh))] (9) and [(IMes)Fe(NDipp)(N(Dipp)C(O)N(p-Pr(i)C6H4))] (10), as well as [NDipp]-group-transfer reactions with CO and Bu(t)NC. Density functional theory calculations suggested that the alkane chain dehydrogenation reaction starts with a hydrogen atom abstraction mechanism, whereas the Si-H activation reaction proceeds in a [2π+2σ]-addition manner. Both reactions have the pathways at the triplet potential energy surfaces being energetically preferred, and have formal iron(IV) hydride and iron(IV) silyl species as intermediates, respectively. The low-coordinate nature and low d-electron count (d(4)) of iron(IV) imido complexes are thought to be the key features endowing their unique reactivity.

The combined use of aminocarbene and divinyltetramethyldisiloxane (dvtms) as supporting ligands enables the access of unprecedented low-coordinate iron(0) alkene compounds [L n Fe(h 2 :h 2 -dvtms)] (L = N-heterocyclic carbene (NHC) or cyclic (alkyl)(amino)carbene (CAAC), n = 1 or 2) from the reactions of FeCl 2 with alkali-metal reducing agents, free aminocarbene ligands, and dvtms. The iron(0) species deliver their {L n Fe 0 } fragments to perform redox reactions with Ph 2 SiH 2 , S 8 , Se, and DippN 3 , furnishing novel aminocarbenesupported iron(IV) silylene, all-ferrous iron-sulfur/selenium cubanes, and bis(imido)iron(IV) compounds. These conversions demonstrate the potential synthetic utility of the carbenesupported iron(0) complexes as a valuable class of lowcoordinate iron(0) reagents.