Abstract
Reactions of the pentaruthenium cluster complexes Ru5(μ5-C)(CO)15 (5), Ru5(μ5-C)(CO)14[μ-η2-O═C(NMe2)](μ-H) (6), and Ru5(μ5-C)(CO)15Cl(μ-H) (7) with ethyne (C2H2) in the presence of Me3NO yielded the zwitterionic complexes Ru5(μ5-C)(CO)13[μ-η2-CHCH(NMe3)] (8), Ru5(μ5-C)(CO)13[μ-η2-O═C(NMe2)](η1-E-CH═CH(NMe3)(μ-H) (9), and Ru5(μ5-C)(CO)13Cl[η1-E-CH═CH(NMe3)](μ-H) (11). Each product contains a positively charged trimethylammonioethenyl ligand, CH═CH(+NMe3), that is derived from a 2-trimethylammonioethenide, -CH═CH(+NMe3), zwitterion that formally has a positive charge on the nitrogen atom and a negative charge on the terminal enyl carbon atom. The trimethylammonioethenyl ligand, CH═CH(+NMe3) in 8 is a η2-ligand that bridges a Ru-Ru bond on a basal edge of the square-pyramidal Ru5 cluster by a combination of σ + π cooordination of the ethenyl group. Compounds 9 and 11 each contain a η1-terminally coordinated [η1-E-CH═CH(+NMe3)] ligand with an E stereochemistry at the C═C double bond in open Ru5 cluster complexes. Compound 9 was decarbonylated to yield the compound Ru5(μ5-C)(CO)12[μ-η2-O═C(NMe2)][μ-η2-CH═CH(NMe3)](μ-H) (10) containing a η2-bridging CHCH(+NMe3) ligand. Compound 10 was converted back to 9 by the addition of CO. Two zwitterionic products, Ru5(μ5-C)(CO)14[η1-E-CH═CH(NMe3)] (12) and Ru5(μ5-C)(CO)15[η1-E-CH═CH(NMe3)] (13), were obtained by the addition of CO to 8. Compound 12 is an intermediate en route to 13. Compound 12 contains a terminally coordinated η1-E-CH═CH(+NMe3) ligand on one of the basal Ru atoms of a square-pyramidal Ru5 cluster. Compound 13 also contains a terminally coordinated η1-E-CH═CH(+NMe3) ligand on the wing-tip bridging Ru atom of a butterfly Ru4C cluster. Treatment of 6 with methyl propiolate (HC≡CCO2Me) yielded the zwitterionic complex Ru5(μ5-C)(CO)13[μ-η2-O═C(NMe2)][η1-E-(MeO2C)C═C(H)NMe3](μ-H) (14) that is structurally similar to 9 but contains a η1-E-(MeO2C)C═C(H)(+NMe3) ligand. Compound 14 eliminated the NMe3 group to yield the compounds Ru5(μ5-C)(CO)13[μ-η2-O═C(NMe2)][μ-η2-(MeO2C)HC═CH] (15) which contains a bridging methoxycarbonyl-substituted alkenyl ligand and the known compound Ru5(μ5-C)(CO)13[μ-η2-O═C(NMe2)](HNMe2)(μ-H) (16).
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