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.