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Issue 31, 2018
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Monomeric Fe(iii) half-sandwich complexes [Cp′FeX2] – synthesis, properties and electronic structure

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The half-sandwich complex [Cp′Fe(μ-I)]2 (1; Cp′ = η5-1,2,4-(Me3C)3C5H2) is cleaved when heated in toluene to form a cation–anion pair [{Cp′Fe(η6-toluene)}+{Cp′FeI2}] (2), in which the two Fe(II) atoms adopt different spin states, i.e., a low-spin (S = 0) and a high-spin (S = 2) configuration. Upon oxidation of 1 with C2H4I2, the thermally stable 15VE species [Cp′FeI2] (3) can be isolated, in which the Fe(III) atom adopts an intermediate spin (S = 3/2) configuration. Complex 3 is an excellent starting material for further functionalizations and it reacts with Mg(CH2SiMe3)2 to form the unprecedented Fe(III) (S = 3/2) bis(alkyl) complex [Cp′Fe(CH2SiMe3)2] (4). The respective spin states of complexes 2–4 are confirmed by single-crystal X-ray crystallography, zero-field 57Fe Mössbauer spectroscopy, and solid-state magnetic susceptibility measurements. In contrast to the related 14VE high-spin (S = 2) Fe(II) alkyl species [Cp′FeCH(SiMe3)2], which resists the reaction with H2 as a consequence of a spin-induced reaction barrier, complex 4 reacts cleanly with H2 (8 bar) in cyclohexane to yield iron hydrides [{Cp′Fe}2(μ-H)3] (5) and [Cp′Fe(μ-H)2]2 (6) in a 1 : 4 ratio. However, when the hydrogenation of 4 is carried out in benzene, a green 19VE [Cp′Fe(η6-C6H6)] (A) intermediate is formed, which dimerizes to the bis(cyclohexadienyl)-bridged product [(Cp′Fe)22–η55-C12H12)] (7). Further evidence for the intermediacy of [Cp′Fe(η6-C6H6)] (A) was gathered by X-band EPR and UV/vis spectroscopy. Interestingly, attempts to oxidize 7 with AgSbF6 proceeded via C–C bond cleavage instead of metal oxidation to form [Cp′Fe(C6H6)][SbF6] (8).

Graphical abstract: Monomeric Fe(iii) half-sandwich complexes [Cp′FeX2] – synthesis, properties and electronic structure

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20 Apr 2018
07 Jun 2018
First published
20 Jun 2018

Dalton Trans., 2018,47, 10517-10526
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Monomeric Fe(III) half-sandwich complexes [Cp′FeX2] – synthesis, properties and electronic structure

M. Reiners, M. Maekawa, D. Baabe, M. Zaretzke, P. Schweyen, C. G. Daniliuc, M. Freytag, J. Raeder, J. Hohenberger, J. Sutter, K. Meyer and M. D. Walter, Dalton Trans., 2018, 47, 10517
DOI: 10.1039/C8DT01570H

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