[Ru(xantsil)(CO)(η⁶-toluene)]: Synthon for a highly unsaturated ruthenium(II) complex through facile dissociation of the toluene ligand [xantsil = (9,9-dimethyIxanthene-4,5-diyl)bis(dimethylsilyl)]

The reactions of [Ru(xantsil)(CO)(η⁶-C₆H ₅CH₃)] [la, xantsil = (9,9-dimethylxanthene-4,5-diyl) bis(dimethylsilyl))] with some electron-donating molecules were reported. When la was dissolved in benzene, benzene replaced the η⁶-toluene ligand easily at room temperature to give [Ru(xantsil)(CO)(η⁶- C₆H₆)] (lb). The η⁶-toluene ligand was also substituted by sterically less demanding two-electron donors smoothly at room temperature to afford [Ru(xantsil)(CO)L₃] (L = CH₃CN (2), BuNC (3), and PMe₃ (4)). The X-ray diffraction studies revealed that they take a typical octahedral geometry, in which the xantsil ligand is coordinated to the Ru(II) center in k²(Si,Si) fashion. Reactions of la with sterically demanding phosphines gave [Ru(xantsil)(CO)(PR₃)] (R = ⁱPr (5) and Cy (6)). According to the X-ray diffraction study, complex 6 takes a square-pyramidal geometry, in which the xantsil ligand is bound to the Ru(II) center in k³(Si1Si1O) fashion and one of the silyl groups occupies the apical position. The coordinatively unsaturated Ru(II) center is slightly stabilized by the agostic interaction by the C-H bonds in PCy₃ [RuH: 2.89 and 3.06 Å]. The highly coordinatively unsaturated nature in 6 was indicated by the reaction with carbon monoxide molecules to give [Ru(xantsil)(CO)₃(PCy₃)] (7) at room temperature. The typical octahedral geometry with the K²(Si,Si)- xantsil ligand was established by the X-ray diffraction study.