Cationic polypnictogen complexes as building blocks for novel ferrocenes

Abstract

The systematic nucleophilic functionalisation of the cationic pentaphosphole ligand complex [Cp*Fe(η⁴-P₅Me)][OTf] ([OTf]⁻ = [SO₃CF₃]⁻) (A) with sterically demanding Cp^R derivatives is reported. This newly developed protocol turned out to be a highly reliable method for the synthesis of end-deck cyclo-P₅ ligand complexes bearing bulky Cp^R substituents. By the reaction of A with anionic Cp^R salts, complexes of the type [Cp*Fe(η⁴-P₅MeCp^R)] (Cp* = η⁵-C₅Me₅; Cp^R = Cp′ (1), Cp″ (2), Cp‴ (3), Cp^Me (4); Cp′ = η⁵-C₅H₄^tBu, Cp″ = η⁵-1,3-^tBu₂C₅H₃, Cp‴ = η⁵-1,3,4-^tBu₃C₅H₂, Cp^Me = η⁵-C₅Me₄H) are obtained. All products feature a selective 1,1′-disubstitution at the cyclo-P₅ ligand. Further reactivity studies of these complexes with FeBr₂ enabled the formation of novel, sterically demanding ferrocene derivatives [{Cp*Fe(η⁴-P₅Me(η⁵-Cp″))}₂Fe] (5) and [Cp*Fe(η⁴-P₅Me(η⁵-Cp″))FeCp″] (6), featuring three different Fe atoms in a ferrocene-like environment. Oxidation of 5 yielded the dicationic complex [{Cp*Fe(η⁴-P₅Me(η⁵-Cp″))}₂Fe][FAl]₂ (7). EPR, zero-field ⁵⁷Fe Mössbauer, as well as DFT investigations on 7 showed a symmetric distribution of the positive charges on the outer Fe atoms.