Complexes of Iron(II) and Iron(III) Containing Aryl-Substituted N-Heterocyclic Carbene Ligands

Abstract

Iron(II) and iron(III) complexes containing the 1,3-dimesitylimidazole-2-ylidene (IMes) and 1,3-bis(2,6diisopropylphenyl)imidazol-2-ylidene (IPr) ligands have been prepared and characterized. Four-coordinate iron(II) carbene species are sensitive to the steric bulk of the carbene ligand and can adopt both monomeric and halide-bridged dimeric structures with 2:1 and 1:1 carbene to iron stoichiometries, respectively. Iron(III) carbene complexes bind a single carbene ligand, which is easily exchanged in solution. The structural and solution phase characterization of all compounds is reported, and their relevance to iron-catalyzed C−C coupling reactions is discussed.

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;…”

Mono-N-heterocyclic carbene amido and alkyl complexes. Cobalt-mediated C–H activation and C–C coupling reactions involving benzyl ligands on a putative 3-coordinate intermediate

“…4,5 In particular, the involvements of iron and cobalt NHC complexes in C-C cross coupling reactions [6][7][8] are recent advancements that have fuelled interest in the isolation of well defined Fe and Co NHC alkyls and aryls and the study of their stoichiometric and catalytic reactivity. [9][10][11][12] An additional emerging area of novel reactivity of Fe and Co organometallics is intra-and inter-molecular C-H activation reactions, which could proceed by mechanisms that are different from those encountered in early or late transition metals, i.e. featuring single electron redox events and homolytic pathways.…”

“…The reaction of IMes with CoCl 2 has recently been reported to proceed also with a 2 : 1 stoichiometry leading to the tetrahedral [Co(Imes) 2 Cl 2 ] which can be further converted to the dinuclear [Co(Imes)Cl-(μ-Cl)] 2 by subsequent reaction with NO + or Ag + . 12 The reaction of CoX 2 , X = Cl, Br, I with IPr gives the respective dinuclear complexes [Co(IPr)X(μ-X)] 2 . 23,24 We observed the same behaviour with CoCl 2 and SIPr giving the dinuclear complex [Co(SIPr)Cl-(μ-Cl)] 2 the structure of which is given in the ESI.…”

Iron(III) Half‐Sandwich Complexes of the Two‐Legged Piano‐Stool [CpFe(aryl)Cl] Type from the Corresponding Aryliron(II) Precursors

“…The Fe–C12 (C ipso ) bond [1.969(4) Å] is shorter than that (2.043 Å) of the aryliron(II) derivative 4 (Scheme ), as expected from the different ionic radii of high‐spin Fe II and Fe III ions . The Fe III –C bonds in N‐heterocyclic carbene complexes are even longer, for example, the Fe–CH 3 distances are 2.060(11) Å in the 17‐valence‐electron iron(III) complex [Cp*Fe(η 3 ‐C 3 H 5 )(CH 3 )] and 2.090(2) Å in the 1,3‐diisopropylimidazol‐2‐ylidene complex of iron(III) chloride . The tert ‐butyl substituent of C‐4 is located directly above the mesityl moiety and bent out of the plane of the cyclopentadienyl ring by ca.…”

“…Palladium(II) chloride did not rearrange the mesityl ligand to form a heterodinuclear species but resulted in the oxidized aryliron complex 5. distances are 2.060(11) Å in the 17-valence-electron iron(III) complex [Cp*Fe(η 3 -C 3 H 5 )(CH 3 )] [12] and 2.090(2) Å in the 1,3-diisopropylimidazol-2-ylidene complex of iron(III) chloride. [13] The tert-butyl substituent of C-4 is located directly above the mesityl moiety and bent out of the plane of the cyclopentadienyl ring by ca. 14.4°for steric reasons.…”