Comparative reactivity of triruthenium and triosmium mu(3)-eta(2)-imidoyls .2. Reactions with alkynes

The reactions of Ru-3(CO)(9)(mu(3)-eta(2)-CH3C=NCH2CH3)(mu-H) (1), M-3(CO)(9)(mu(3)-eta(2)-C=N(CH2)(3))(mu-H) (M = Ru (2), M = Os (3)) with the alkynes RC=CR (R = CH3, C6H5, CO2Me) have been studied. The ruthenium complexes 1 and 2 react with 2-butyne at 70 degrees C to give two very different trimetallic alkyne derivatives: Ru-3(CO)(7)(mu-eta(2):eta(4)-C-4(CH3)(4))(mu-eta(2)-CH3C=NCH2CH3)(eta(1)-COC(CH3)C(H)CH3) (5) and Ru-3(CO)(8)(mu(3)-eta(2)-C=N(CH2)(3))(mu-eta(2)-CH3C(H)=CCH3) (6). The osmium imidoyl 3 does not react with 2-butyne even at elevated temperatures. However, the reaction of Os-3(CO)(9)(mu-eta(2)-C=N(CH2)(3))(mu-H)(CH3CN) (7b), synthesized from Os-3(CO)(10)(mu-eta(2)-C=N(CH2)(3))(mu-H) (7a), with 2-butyne yields the analog of 6, Os-3(CO)(8)(mu(3)-eta(2)-C=N(CH2)(3))(mu-eta(2)-RC(H)=CR) (R = CH3 (10), R = C6H5 (11)) on thermolysis of the initially formed nonacarbonyl precursors (8 and 9 for R = CH3), which are a mixture of isomers. Direct reaction of 7a with diphenylacetylene at 100 degrees C gives somewhat lower yields of 11. The reaction of 7b with dimethylacetylenedicarboxylate or the direct reaction of 3 with this alkyne yields the nonacarbonyl derivative Os-3(CO)(9)(mu-eta(2)-C=N(CH2)(3))(mu(3)-eta(3)-CH3O2CC=C(H)CO2CH3) (12). Direct reaction of 7a with a 2.5 molar excess trimethylamine N-oxide at room temperature yields the alkyne-imidoyl-coupled product Os-3(CO)(8)(mu-eta(6)-CH3C(H)=C(CH3)C(CH3)=C(CH3)C=N(CH2)(3)) (13) The solid state structures of 5, 11, 12, and 13 are reported. A comparative study of the electrochemical properties of 5 and 1 is also reported.