Organorhodium and Iridium-Containing Derivatives of the 48-Tungsto-8-phosphate Wheel: Synthesis, Characterization, and Catalytic Activity

We report on the synthesis, characterization, and catalysis of organorhodium- and iridium-containing derivatives of the 48-tungsto-8-phosphate wheel, [{Rh(Cp*)(H₂O)}₄P₈W₄₈O₁₈₄]³²⁻ (1) and [{Ir(Cp*)(H₂O)}₄P₈W₄₈O₁₈₄]³²⁻ (2). The novel polyanions 1 and 2 were synthesized by the reaction of (MCp*Cl₂)₂ (M = RhIII, IrIII) with the mixed potassium-lithium salt of the cyclic P₈W₄₈ precursor in an aqueous medium using mild one-pot conditions, and four organometallic moieties are covalently bound to the central cavity of the P₈W₄₈ wheel via two M-O(W) oxygen bridges. Both polyanions were structurally characterized in the solid state by single-crystal X-ray diffraction, FT-IR spectroscopy, and thermogravimetric analysis, as well as in solution by ³¹P and ¹³C NMR spectroscopy. The hydrogenation of olefins was investigated after supporting polyanions 1 and 2 on mesoporous SBA15. The supported catalysts exhibited high activity in the selective hydrogenation of o-xylene with very little cracking products, even under high temperature and pressure conditions.