Activation of Triphenylphosphine Oxide Mediated by Trivalent Organouranium Species

Treating a family of uranium benzyl compounds, Tp*₂U­(CH₂Ph) (1-Bn), Tp*₂U­(CH₂-para-ⁱPrPh) (1-ⁱPr), Tp*₂­U­(CH₂-para-^tBuPh) (1-^tBu), or Tp*₂­U­(CH₂-meta-OMePh) (1-OMe), which are supported by two hydro­tris­(3,5-di­methyl­pyra­zolyl)­borate (Tp*) ligands, with a single equivalent of triphenylphosphine oxide (OPPh₃) causes a unique carbon–carbon coupling to occur. The products of this reaction, Tp*₂U­[OP­(C₆H₅)₂­(C₆H₅­CH₂­C₆H₅)] (2-Ph), Tp*₂U­[OP­(C₆H₅)₂­(C₆H₅­CH₂-p-iPr­C₆H₄)] (2-ⁱPr), Tp*₂U­[OP­(C₆H₅)₂­(C₆H₅­CH₂-p-tBu­C₆H₄)] (2-^tBu), and Tp*₂U­[OP­(C₆H₅)₂­(C₆H₅­CH₂-m-OCH_3­C₆H₄)] (2-OMe), are characterized by coupling between the benzyl substituent and the para-carbon of one of the phenyl groups of OPPh₃. To probe the scope of this unusual reactivity, 1-Bn was treated with different tris­(aryl)­phos­phine oxides, including tris­(p-tolyl)­phos­phine oxide, which yields Tp*₂U­[OP­(p-tolyl)₂­(C₆H₄­(CH₃)­CH₂­C₆H₅)] (3-tolyl). All compounds were characterized by multinuclear NMR, vibrational, and electronic absorption spectroscopies. When possible, X-ray diffraction was used to confirm molecular structures.