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

Abstract

Metathesis of [Cp′FeI]₂ (1) with KHBEt₃ affords the polyhydride iron complexes [Cp′FeH₂]₂ (2) and [Cp′₂Fe₂H₃] (3). The ratio in which both 2 and 3 are obtained correlates to the applied H₂ pressure during synthesis. Complex 2 activates CH- or CD- bonds in aromatic compounds and shows slow H/D exchange in the presence of D₂ at room temperature in cyclohexane solvent. [Cp′FeH₂]₂ acts as a Cp′Fe(I)-synthon when reacted with white phosphorus (P₄) to give [Cp′Fe]₂(μ-P₄) (4) as the only P-containing product. This complex is best described as a triple-decker complex with a planar arrangement of a severely distorted kite-like cyclo-P₄ unit. This distortion persists in solution and solid state as evidenced by a small PP coupling constant in the ³¹P{¹H} NMR spectrum and a long P–P distance of 2.53 Å. Complex 4 is an isomer to the long-known [{Cp′Fe}₂(μ-η⁴:η⁴-P₄)] (5) with a cis-tetraphosphabutadiene moiety and it thermally rearranges to 5, [{Cp′Fe}₂(μ-η³:η³-P₃)] and [Cp′Fe(P₅)]. All complexes described in this paper have been completely characterized including X-ray crystallography, variable temperature NMR studies and DFT calculations. Relaxed force constants (inverse compliance constants) are used as bond strength descriptors.