The octahedrally coordinated bis(ether-phosphine)ruthenium(II) complexes Cl4Ru(P O)(2) (1a-c) (P O, eta(2)(O,P)-chelated ether-phosphine; a, Ph(2)PCH(2)CH(2)OCH(3); b, Ph(2)PCH(2)C(4)H(7)O(2); c, Cy(2)PCH(2)CH(2)OCH(3)) represent potentially unsaturated 14-electron metal species which are weakly protected by intramolecular chelation of the ether moiety. The ease of Ru-O bond cleavage is shown by the reaction with a variety of small molecules. Sulfur dioxide, acetonitrile, and tert-butyl isocyanide are readily added to 1a-c to generate the corresponding complexes Cl2Ru(P similar to O)(P O)(eta(1)-SO2) (2a-c) (P similar to O, eta(1)(P)-coordinated ether-phosphine), Cl2Ru(CH3CN)(P similar to O)(P O) (4a-c), and Cl2Ru(CNCMe(3))(2)(P similar to O)(2)(8a-c), respectively. The action of carbon disulfide on 1c affords an insertion into the Ru-P bond to give the phosphoniodithiocarboxylato complex Cl2Ru(S2CP similar to O)(P O) (5c). Phenylacetylene is activated by the starting complexes 1a-c to yield the vinylidene compounds Cl2Ru(=C=CHPh)(P similar to O)(P O) (3a-c). All complexes are accessible under moderate reaction conditions in almost quantitative yields. The fluxional behavior of a variety of substrate complexes in solution was investigated by temperature-dependent P-31{H-1} NMR spectroscopy, Remarkably, the vinylidene complexes 3a,b show complex exchange phenomena which account for two dynamic processes. The structures of 2a, 3a, 3c, trans-Cl2Ru(CNCMe(3))(P similar to O)(P O) (9a), and cis-Cl2Ru(CNCMe(3))(P similar to O)(P O) (10b) were determined by single-crystal X-ray diffraction. Aside from the coordinated small molecules, the structures of 3c and 9a are similar with trans-arranged phosphines, whereas 2a, 3a, and 10b are set up with cis-positioned phosphines. 2a and 10b crystallize in the monoclinic space group P2(1)/c with Z = 4, and 3a, 3c, and 9a have the triclinic space group P $(1) over bar$$ with Z = 2. The cell dimensions are as follows: for 2a, a = 18.991(7) Angstrom, b = 9.717(3) Angstrom, c = 19.930(6) Angstrom, beta = 110.94(3)degrees; for 3a, a = 9.687(1) Angstrom, b = 11.768(2) Angstrom, c = 16.386(2) Angstrom, alpha = 103.08(1)degrees, beta = 103.84(1)degrees, gamma = 01.37(1)degrees; for 3c, a = 12.420(2) Angstrom, b = 12.621(2) Angstrom, c = 13.556(2) Angstrom, alpha = 91.66(3)degrees, beta = 103.84(1)degrees, gamma = 91.37(1)degrees; for 3c, a = 9.416(2) Angstrom, b = 12.791(2) Angstrom, c = 15.665(4) Angstrom, alpha = 79.39(2)degrees, beta = 76.59(2)degrees, gamma = 78.43(1)degrees, for 10b, a = 9.870(3) Angstrom, b = 11.171(4) Angstrom, c= 34.778(14) Angstrom, beta = 93.27(4)degrees.