High-spin Cyclopentadienyl Complexes, Part 7. Ambivalent Interpretation of the Bonding in Iron-Copper Complexes: Metalated Arene versus Carbocyclic Carbene

Abstract

The electron distribution within a mesityl ligand bridging a cyclopentadienyliron fragment attached to the mesityl π system and a second metal fragment connected to the ipso carbon of the mesityl ring has been probed using a copper(I) halide as a component in [CpmFe (μ,η5 :η1-C6H2Me3)CuCl] (2) and its copper bromide derivative 3. This approach minimizes steric effects and allows for DFT calculations the results of which are in very good agreement with structural data. The calculations show a significant carbene character already for the bare phenyl anion as a result of electrostatic repulsion of the lone pair pushing the π electrons away from the ipso carbon towards the para carbon atom of the aromatic ring. π Coordination of a cyclopentadienyliron(II) fragment to the phenyl anion to form a hypothetical sandwich complex does not change this situation. The iron center rather follows the unsymmetric distribution of π charge with an unsymmetrical coordination to the π system. Coordination of a copper(I) chloride moiety to the phenyl anion or to the hypothetical π complex [CpFe(C6H5)] in both cases equally lowers that carbene character by attracting the lone pair of the ipso carbon and thus decreasing its repulsive influence on the π electrons.

Reactivity studies on [Cp′FeI]2: From iron hydrides to P4-activation

“…11,12 These species can be obtained as stable compounds and react with substituted phenolates to yield monomeric and dimeric complexes depending on the steric bulk of the phenolate ligand. 12 More recently s/p-rearrangements of aryl ligands connected to the Cp 0 Fe-fragment have been reported, [13][14][15] whereas the related 5 CpFe(C 5 H 3 -2,6-(iPr) 2 ) derivative is a singlemolecule magnet. 16 The synthesis of organophosphorus compounds directly from elemental phosphorus is a challenging process for chemists and the chemical industry, and involves the hazardous chlorination of P 4 to PCl 3 .…”

Heterocycle Syntheses with Anionic N‐Heterocyclic Carbenes: Ring Transformations of Sydnone Imine Anions

“…These reactions are supposed to be trapping reactions of NHCs, and they have been described for imidazole‐2‐ylidene, pyrazol‐3‐ylidene, indazol‐3‐ylidene as well as several organolithium compounds. Thus, phenyllithium reacts with isocyanates, isothiocyanates, and carbon dioxide; similarly, the non‐complexed phenyl anion was calculated to have a significant carbene character . To study the behavior of sydnone imine anions toward heterocumulenes, we reacted freshly prepared samples of deprotonated sydnone imines with tolyl isocyanate, tolyl isothiocyanate and p ‐chlorophenyl isocyanate.…”

Iron‐Mediated Coupling of Two Ethyl Anions to Form a 2‐Butyne Ligand

“…The σ‐aryl complex 6 2 (Scheme ) rearranges with trimethylaluminum to the π‐arene complex [ 4 CpFe(μ,η 6 :η 1 ‐C 6 H 3 i Pr 2 ‐2,6)AlMe 3 ] ( 7 ), which contains an aryltrimethylaluminato ligand. Under an inert gas atmosphere, complex 7 decomposes slowly upon heating at temperatures as low as 65 °C.…”

“…High‐spin iron(II) aryl complexes1 of the [CpFe–R] type (Cp = cyclopentadienyl derivative, R = σ‐aryl ligand) with bulky alkylcyclopentadienyl ligands are readily available from the corresponding cyclopentadienyliron(II) halides and aryl Grignard compounds and show a σ/π rearrangement reaction with Lewis acids such as copper(I) chloride2,3 or organometallic complexes with low coordination number 4. Such reactions give rise to iron–arene π complexes with the introduction of the Lewis acid as a σ‐bound arene substituent.…”