Some ruthenium derivatives of penta-1,4-diyn-3-one

The reaction between Ru(C≡CH)(dppe)Cp* (1) and oxalyl chloride affords ({Ru(dppe)Cp*}C≡C)2CO (2) in 72% yield. Methylation (MeOTf) of 2 occurs first on the carbonyl oxygen, affording [({Ru(dppe)Cp*}C≡C)2C(OMe)]OTf ([3]OTf). A second methylation of [3]+ on the alkynyl Cβ proceeds slowly, affording [{Cp*(dppe)Ru}CCMeC(OMe)CC{Ru(dppe)Cp*}][OTf] 2 ([4][OTf]2), whereas protonation of [3]+ occurs readily to give crystallographically characterized [{Cp*(dppe)Ru} CCHC(OMe)CC{Ru(dppe)Cp*}][OTf]2 ([5][OTf]2). The molecular structures of [3]OTf and [5][OTf]2 suggest that polarization by the CO group results in significant contributions from the alkynyl-allenylidene or alkynyl-carbyne mesomers, respectively. Reaction of 2 in refluxing MeOH containing [NH4]PF6 results in partial methanolysis to give Ru{C≡CC(O)CH=CH(OMe)}(dppe)Cp* (6). Knövenagel condensation of 2 with CH2(CN)2 affords {[Ru(dppe)Cp*]C≡C}2C=C(CN)2 (7). The related asymmetric complex {Cp*(dppe)Ru}C≡C[C=C(CN)2] C≡CC≡C{Ru(dppe)Cp*} (8) was obtained from the reaction between Ru{C≡CC(CN)=C(CN)2}(dppe)Cp* and lithiated Ru(C≡CC≡CH)(dppe)Cp*. Single-crystal structural determinations of 2, [3]OTf, [5][OTf]2, 6, 7, and 8 are reported, together with a supporting computational study of relevant electronic structures. © 2013 American Chemical Society.Michael I. Bruce, Alexandre Burgun, Mark A. Fox, Martyn Jevric, Paul J. Low, Brian K. Nicholson, Christian R. Parker, Brian W. Skelton, Allan H. White, and Natasha N. Zaitsev