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

Reactions of the pentaruthenium cluster complexes Ru-5(mu(5)-C)(CO)(15) (5), Ru-5(mu(5)-C)(CO)(14)[mu-eta(2)-O=C(NMe2)](mu-H) (6), and Ru-5(mu(5)-C)(CO)(15)Cl(mu-H) ( 7) with ethyne (C2H2) in the presence of Me3NO yielded the zwitterionic complexes Ru-5(mu(5)-C)(CO)(13)[ mu-eta(2)-CHCH(NMe3)] (8), Ru-5(mu(5)-C)(CO)(13)[mu-eta(2)-O=C(NMe2)](eta(1)-E-CH=CH(NMe3)(mu-H) (9), and Ru-5(mu(5)-C)(CO)(13)Cl[eta(1)-E-CH=CH(NMe3)](mu-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 eta(2)-ligand that bridges a Ru-Ru bond on a basal edge of the square-pyramidal Ru-5 cluster by a combination of sigma + pi cooordination of the ethenyl group. Compounds 9 and 11 each contain a eta(1)-terminally coordinated [eta(1)-E-CH=CH(Me-+(3))] ligand with an E stereochemistry at the C=C double bond in open Ru-5 cluster complexes. Compound 9 was decarbonylated to yield the compound Ru-5(mu(5)-C)(CO)(12)[mu-eta(2)-O=C(NMe2)][mu-eta(2)-CH=CH(NMe3)](mu-H) (10) containing a eta(2)-bridging CHCH(+NMe3) ligand. Compound 10 was converted back to 9 by the addition of CO. Two zwitterionic products, Ru-5(mu(5)-C)(CO)(14)[eta(1)-E-CH=CH(NMe3)] (12) and Ru-5(mu(5)-C)(CO)(15)[eta(1)-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 eta(1)-E-CH=CH(+NMe3) ligand on one of the basal Ru atoms of a square-pyramidal Ru-5 cluster. Compound 13 also contains a terminally coordinated eta(1)-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 Ru-5(mu(5)-C)(CO)(13)[mu-eta(2)-O=C(NMe2)][eta(1)-E-(MeO2C)C=C(H)NMe3](mu-H) (14) that is structurally similar to 9 but contains a eta(1)-E-(MeO2C)C=C(H)(+NMe3) ligand. Compound 14 eliminated the NMe3 group to yield the compounds Ru-5(mu(5)-C)(CO)(13)[mu-eta(2)-O=C(NMe2)][mu-eta(2)-(MeO2C)HC=CH] (15) which contains a bridging methoxycarbonyl-substituted alkenyl ligand and the known compound Ru-5(mu(5)-C)(CO)(13)[mu-eta(2)-O=C(NMe2)](HNMe2)(mu-H) (16).

Automated summary

In the presence of Me3NO, reactions of Ru-5 cluster complexes with ethyne produced zwitterionic complexes containing positively charged trimethylammonioethenyl ligands, featuring a variety of ligands like eta(2)-ethenyl and eta(1)-ethenyl, along with processes involving decarbonylation and carboxyl addition.