Synthesis and reactivity of {Ru(p-cymene)}2+ derivatives of [Nb6O19]8−: a rational approach towards fluxional organometallic derivatives of polyoxometalates

Abstract

Three {Ru(p-cym)}²⁺ (p-cym = p-cymene) derivatives of [Nb₆O₁₉]⁸⁻—[Nb₆O₁₉{Ru(p-cym)}]⁶⁻ (Nb₆Ru₁), trans-[Nb₆O₁₉{Ru(p-cym)}₂]⁴⁻ (t-Nb₆Ru₂), and [Nb₆O₁₉{Ru(p-cym)}₄] (Nb₆Ru₄)—have been synthesized in water by reaction between [Ru(p-cym)Cl₂]₂ and the hexaniobate. In the solid state, Nb₆Ru₁ and Nb₆Ru₄ have been characterized by IR and EDX spectroscopies, whereas t-Nb₆Ru₂ has been characterized by IR spectroscopy and single-crystal X-ray diffraction (crystal data for K₄-trans-[Nb₆O₁₉{Ru(p-cym)}₂]·14H₂O (K₄-t-Nb₆Ru₂·14H₂O). In solution, all compounds were characterized by ¹H NMR and ESI mass spectrometry analyses, and Nb₆Ru₁ was also analyzed by ¹⁷O NMR. These studies allowed a comparison of the differences in behaviour of the three complexes in water: Nb₆Ru₁ is particularly stable, Nb₆Ru₄ decomposes by loss of {Ru(p-cym)}²⁺ fragments, and trans-[Nb₆O₁₉{Ru(p-cym)}₂]⁴⁻ isomerizes into cis-[Nb₆O₁₉{Ru(p-cym)}₂]⁴⁻. A rational mechanism for the isomerisation of t-Nb₆Ru₂ is proposed on the basis of a kinetic study.