Reactive Sigma-Aryliron Complexes or Iron-Promoted Coupling of Two Phenyl Anions to One Bis(cyclohexadienylidene) Ligand: Synthesis, Structure, Mass Spectrometry, and DFT Calculations

A reaction of the bulky alkylcyclopentadienyliron(II) high-spin complex [Cp'Fe(mu-Br)](2) (1a) (Cp' = C5H2(CMe3)(3)-1,2,4) with phenylmagnesium bromide produced the deep blue dinuclear complex [{Cp'Fe}(2)(mu,eta(5):eta(5)-H5C6=C6H5)](2) with a bridging(cyclohexadienylidene) ligand. Its structural analysis shows it centrosymmetric dimer. Each tri(tert-t-butyl)cyclopentadienyliron fragment is eta(5)- coordinated to a cyclohexadienylidene moiety in which one carbon atom is bent out of the plane by 0.39 angstrom, exhibiting a bond length of 1.370 angstrom to its symmetry equivalent. Electrospray ionization mass spectra (EST-MS) from acetonitrile solution confirm nicely the elemental composition of 2 by way of their isotope patterns. Reaction of I a or its tetraisopropylcyclopentadienyl analogue [(CpFe)-Cp-4(mu-Br)](2) (1b) (Cp-4=C5H(CHMe2)(4)) with 2,6-diisopropylphenylmagnesium bromide affords the extremely air-sensitive, paramagnetic sigma-aryl complexes [Cp'Fe((C6H3Pr2)-Pr-i)] (3a) or [(CpFe)-Cp-4((C6H3Pr2)-Pr-i)] (3b), whose Cp-4-Fe distance of 1.92 angstrom is typical for cyclopentadienyliron high-spin complexes. In reactions with copper(l) halides 3a is rearranged to a diamagnetic T complex and coordinated via the ipso carbon atom of the six-membered ring to copper(I) halide fragments to form heterodinuclear complexes [Cp'Fe(mu,eta(5):eta(1)-(C6H3Pr2)-Pr-i)CuCl] (4-Cl) and [Cp'Fe(mu,eta(5):eta(1)-(C6H3Pr2)-Pr-i)CuBr] (4-Br). ESI mass spectra of complexes 4 do not show the molecular cations, but fragmentation to cyclopentadienyhron arene cations and formation of the hexa(tert-butyl)ferrocenium cation on one hand and fusion of complex fragments to oligonuclear complexes with or without inclusion of oxygen or fragments of solvent molecules Oil the Other hand. Three of these oligonuclear complexes formed under the conditions of the ESI-MS experiment, whose elemental composition Could be derived from isotope patterns, have been interpreted as (Cp'Fe(mu,eta(5):eta(1)-(C6H3Pr2)-Pr-i)Cu(mu,eta(1):eta(5)-(OC6H3Pr2)-Pr-i)FeCp'](+) and [{Cp'Fe(mu,eta(5):eta(1)-(C6H3Pr2)-Pr-i)Cu}(2)X](+) (X = Cl, Br). DFT calculations Support the structural analysis of 2 and predict the Structure of the dication 2 2-1. The crystal Structures obtained by X-ray diffraction for 2 and A are reported.