Synthesis, Structures, and Transformations of Bridging and Terminally-Coordinated Trimethylammonioalkenyl Ligands in Zwitterionic Pentaruthenium Carbido Carbonyl Complexes.

Reactions of the pentaruthenium cluster complexes Ru(μ-C)(CO) (), Ru(μ-C)(CO)[μ-η-O═C(NMe)](μ-H) (), and Ru(μ-C)(CO)Cl(μ-H) () with ethyne (CH) in the presence of MeNO yielded the zwitterionic complexes Ru(μ-C)(CO)[μ-η-CHCH(NMe)] (), Ru(μ-C)(CO)[μ-η-O═C(NMe)](η--CH═CH(NMe)(μ-H) (), and Ru(μ-C)(CO)Cl[η--CH═CH(NMe)](μ-H) (). Each product contains a positively charged trimethylammonioethenyl ligand, CH═CH(NMe), that is derived from a 2-trimethylammonioethenide, CH═CH(NMe), 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(NMe) in is a η-ligand that bridges a Ru-Ru bond on a basal edge of the square-pyramidal Ru cluster by a combination of σ + π cooordination of the ethenyl group. Compounds and each contain a η-terminally coordinated [η--CH═CH(NMe)] ligand with an stereochemistry at the C═C double bond in open Ru cluster complexes. Compound was decarbonylated to yield the compound Ru(μ-C)(CO)[μ-η-O═C(NMe)][μ-η-CH═CH(NMe)](μ-H) () containing a η-bridging CHCH(NMe) ligand. Compound was converted back to by the addition of CO. Two zwitterionic products, Ru(μ-C)(CO)[η--CH═CH(NMe)] () and Ru(μ-C)(CO)[η--CH═CH(NMe)] (), were obtained by the addition of CO to . Compound is an intermediate en route to . Compound contains a terminally coordinated η--CH═CH(NMe) ligand on one of the basal Ru atoms of a square-pyramidal Ru cluster. Compound also contains a terminally coordinated η--CH═CH(NMe) ligand on the wing-tip bridging Ru atom of a butterfly RuC cluster. Treatment of with methyl propiolate (HC≡CCOMe) yielded the zwitterionic complex Ru(μ-C)(CO)[μ-η-O═C(NMe)][η--(MeOC)C═C(H)NMe](μ-H) () that is structurally similar to but contains a η--(MeOC)C═C(H)(NMe) ligand. Compound eliminated the NMe group to yield the compounds Ru(μ-C)(CO)[μ-η-O═C(NMe)][μ-η-(MeOC)HC═CH] () which contains a bridging methoxycarbonyl-substituted alkenyl ligand and the known compound Ru(μ-C)(CO)[μ-η-O═C(NMe)](HNMe)(μ-H) ().