Diphosphacarborane analogues of ferrocene: The synthesis of two isomeric twelve-vertex closo-[(η5-C5H5)FeP2CB8H9] complexes

Abstract

The reaction of the Tl⁺ salt of the [nido-7,8,9-P₂CB₈H₉]⁻ anion (1⁻) with [CpFe(CO)₂I] (Cp = η⁵-C₅H₅) in refluxing mesitylene for 12 h gives mixed-sandwich [1-Cp-closo-1,2,3,4-FeP₂CB₈H₉] (2) (yield 63%). Reaction of the PPh₄⁺ salt of the isomeric [nido-7,8,10-P₂CB₈H₉]⁻ anion 3⁻ with [CpFe(CO)₂I] in refluxing mesitylene gives [1-Cp-closo-1,2,3,5-FeP₂CB₈H₉] (4) (yield 56%), isomeric with 2. Compound 4 also results (yield 92%) from the sublimation of 2 under argon at ca. 350 °C. The constitution of all compounds is established by mass spectrometry, IR spectroscopy and multinuclear NMR spectroscopy (¹H, ¹¹B, ³¹P, and ¹³C; two-dimensional [¹¹B–¹¹B]-COSY, and ¹H–{¹¹B(selective)), further confirmed in the case of 4 by a single-crystal X-ray diffraction analysis.