The tetrahydride-bridged complex ( C~M~~) R U (~-H )~R U ( C~M~~)(2) is synthesized by the reaction of [(C5Mes)RuCl212 (1) with LiAlH4, which is characterized as a classical hydride complex on the basis of the 2' 1 value and X-ray diffraction study. In the presence of acid, 2 decomposes to form a coordinatively unsaturated species, which is trapped by the 6-electron ligands to yield the cationic Welectron complexes. Treatment of 2 with ethylene yields (C5Me5)-Ru(CsMe5) (9), structural analogue of the intermediate 8. Thermolysis of 6 in toluene at 60 "C under 1 atm of ethylene generates a dinuclear ruthenacyclopentadiene complex ((25-
M~~)R~(CHFCH~)(CM~=CHCH=CM~)R~(CSM~~)(10) as a result of the C-C coupling reaction among the coordinated ethylene and two vinyl ligands. The bis(palky1idene) complex (C6Me5)Ru(pL-CHMe) [pCMe(CH=CHCOMe)Ru(C5Me6) (13) which seems to be a model compound of the intermediate of the cyclometalation leading to 10 is obtained upon heating a divinyl complex (C~M~~)RU(CHFCHCOM~)(CH=CH~)~RU(C~M~~) (12) in refluxing toluene. The ethylene molecule coordinated in 10 inserts into the Ru-C bond of the ruthenacyclopentadiene to form (CsMes)Ru(CMe=CHCH=CMeCH=CH2)(p-H)Ru(CsMe5) (16) when 10 is heated in toluene at 110 "C. Regioselective insertion of a,P-unsaturated ketones into the Ru-C bond of the ruthenacycle giving (C5Me5)Ru(CMe=CHCH=CMeCR1=CCOR2) (p-H)Ru(C5Me5) (17, R1 = H, R2 = Me; 18, R1, R2 = (CH2)2; 19, R', R2 = (CH2)3) is demonstrated in the thermolysis of 10 in the presence of methyl vinyl ketone, cyclopentenone, and cyclohexenone. The molecular structures of several of the products are determined by single-crystal X-ray diffraction studies. Crystal data for 2: space group P 2 / a , a = 12.291(2) A, b = 8.521(1) A, c = 10.053(2) A, = 108.52(1)", V = 998.3(3) A3, and Dcdcd = 1.585 g cm3 for Z = 2. Least-squares refinement based on 2391 reflections converged to R = 0.0220 and R, = 0.0220. Crystal data for 6: space group PI, a = 11.335(2) A, b = 14.315(2) A, c = 8.401(2) A, a = 95.09(2)", p = 117,18(1)", y = 94.36(1)", v = 1197.4(6) A3, and D d c d = 1.538 g cm3 for z = 2. Least-squares refinement based on 2621 reflections converged to R = 0.0900 and R, = 0.1581. Crystal data for 9: space group Pbca, a = 17.876(2) A, b = 20.896(2) A, c = 17.690(2) A, V = 6608(1) g cm3, andDcdcd = 1.529 g cm3 for Z = 8. Least-squares refinement based on 2186 reflections converged to R = 0.057 and R, = 0.040. Crystal data for 10: space group P21/n, a = 14.882(2) A, b = 19.718(4) A, c = 8.794(1) A, = 92.30(2)", v = 2578.5(8) A3, and Dcdcd = 1.496 g ~m -~ for z = 4. Least-squares refinement based on 5731 reflections converged to R = 0.044 and R, = 0.041. Crystal data for 13: space group P21/a, a = 17.210(6) A, b = 9.693(6) A, c = 16.037(7) A, p = 100.366(3)", V = 2632(2) A3, andDdcd = 1.506 g ~m -~ for Z = 4. Least-squares refinement based on 3781 reflections converged to R = 0.037 and R, = 0.035. Crystal data for 16: space group E 1 / a , a = 18.814(2) A, b = 9.212(5) A, c = 15.068(5) A, p = 100.31(2)O, V = 2569(2)...