The 16-electron complex Cp(*)RuCl(P similar to O) (2; Cp(*) = eta(5)-C(5)Me(5); P similar to O = eta(1)(P)-coordinated ligand) was synthesized by reaction of oligomeric [Cp(*)RuCl(2)](n) (1) with the basic ether-phosphine (C6H11)(2)PCH2CH2OCH3 (O,P) in the presence of zinc. Carbonylation of 2 afforded. the chloro carbonyl species Cp(*)RuCl(CO)(P similar to O) (3), which was converted into the cationic, monochelated compound [Cp(*)Ru(CO)(P boolean AND O)][BPh(4)](4[BPh(4)]; P boolean AND O = eta(2)(O,P)-chelated ligand) by chloride abstraction with NaBPh(4). The structure of 4 was elucidated by a single-crystal X-ray structural analysis. 4 crystallizes in the monoclinic space group P2(1)/c with Z = 4. The cell dimensions are a = 11.739(3) Angstrom, b = 17.620(5) Angstrom, c = 22.919(6) Angstrom, and beta = 98.80(2)degrees. The cleavage of the Ru-O bond was achieved by 2 bar pressure of carbon monoxide, resulting in the formation of the dicarbonyl complex [Cp(*)Ru(CO)2(P similar to O)][BPh(4)] (5[BPh(4)]). By treatment of 4 with triphenylphosphine the mixed-phosphine derivative [Cp(*)Ru(CO)-(P similar to O)(PPh(3))][BPh(4)] (6[BPh(4)]) was formed. A single-crystal X-ray structural determination of 6 shows that it crystallizes in the monoclinic space group Cc with Z = 4. The cell dimensions are a = 25.683(6) Angstrom, b = 15.496(4) Angstrom, c = 15.653(7) Angstrom, and beta = 110.96(3)degrees.