Dinuclear Iron(0) Complexes of N-Heterocyclic Carbenes

Abstract

The synthesis, structures, and reactivity of dinuclear Fe 0 complexes of N-heterocyclic carbenes (NHCs, denoted as L) are reported. The NHC adducts of ferric chloride (L)FeCl 3 were prepared from the reactions of FeCl 3 with L in toluene. The reduction of (L)FeCl 3 with KC 8 resulted in the formation of the dinuclear Fe 0 complexes Fe 2 {μ-η 1 (C):η 6 (arene)-L} 2 (2a, L = 1,3-bis(2,4,6trimethylphenyl)imidazol-2-ylidene (IMes); 2b, L = 1,3bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr)), in which NHC ligands bridge two iron atoms using one of the arene rings as an η 6 ligand. Their magnetic properties are different: 2a is paramagnetic and 2b is diamagnetic. The dinuclear complexes 2a,b serve as precursors for monomeric (NHC)Fe 0 species, and treatment of 2a,b with 1 atm of CO led to the formation of (L)Fe(CO) 4 . Complex 2a was found to react with 1-azidoadamantane, giving rise to the dinuclear tetrazene complex (IMes)Fe(μ-NAd) 2 Fe(AdNNNNAd) (4).

(Aminocarbene)(Divinyltetramethyldisiloxane)Iron(0) Compounds: A Class of Low‐Coordinate Iron(0) Reagents

“…The majority of iron(0) species feature strong π‐accepting ligands and/or higher coordination numbers as exemplified by the classical tricarbonyliron(0) alkene compounds,3a the cot complexes [(BAC)Fe(η 4 ‐cot) 2 ] and [(BAC) 2 Fe(η 4 ‐cot)] (BAC: bis(diisopropylamino)cyclopropenylidene),3g and the π‐arene complexes [Fe{( Dipp C) 2 CH 2 }(η 6 ‐(C 6 H 5 R)]11c and [(μ‐η 1 (C):η 6 (arene)‐NHC)Fe] 2 (NHC=IMes, IPr) 12. On the other hand, iron(0) species with relatively weaker ligand fields or low‐coordination number, such as [Fe(PMe 3 ) 4 ],13 [Fe{( Dipp C) 2 CH 2 }(PMe 3 ) 2 ],11c [Fe(IMes) 2 ],14 and [(PEt 3 ) 2 Fe{η 2 ‐(CH 2 CH 2 )} 2 ]15 are prone to intramolecular cyclometallation or decomposition.…”

Iron-catalysed substrate-directed Suzuki biaryl cross-coupling

“…We have undertaken a variety of mechanistic studies, the first of which was to establish the lowest thermodynamically viable oxidation state that can be accessed by iron under the reaction conditions, since Fe(0), [33][34][35] , Fe(I) 36,37 and Fe(II) [38][39][40] complexes can all be supported by NHC ligands. 41 The boronate nucleophile acts as a reducing reagent for the iron;…”

Taming the Antiferromagnetic Beast: Computational Design of Ultrashort Mn−Mn Bonds Stabilized by N‐Heterocyclic Carbenes

“…In parallel with the extraordinary development of the coordination chemistry of NHCs with main group and mononuclear transition metal species, these ligands have also been used to prepare stable derivatives of low‐valent metal compounds featuring metal‐metal bonds. Indeed, complexes of dinuclear Fe 0 stabilized by IMes and IDipp were synthesized, with Fe‐Fe distances of 2.621 and 2.583 Å [44] . Stable low‐valent, dinuclear metal‐metal systems were also obtained by coordination with cyclic (alkyl)(amino) carbenes (CAAC), [45] particularly for homonuclear Au [46] and Co [47] motifs.…”