Reactions of [Ru3(CO)10(μ-dppf)] with Internal Alkynes: A Fine Balance between C–H and P–C Oxidative-Addition to the Triruthenium Center

The reactivity of [Ru3(CO)10(μ-dppf)] (1) [dppf = 1,1′-bis(diphenylphosphino)ferrocene] toward internal alkynes, RC≡CR (R = Et, Ph, CO2Me, CO2Et), has been explored. Isolated products vary with the nature of the alkyne substituent and differ from those generated with related diphosphine-stabilized triruthenium clusters. In all products, one or two equivalents of alkyne are incorporated and three or four carbonyls are lost. With hex-3-yne, the allenyl cluster [Ru3(CO)7(μ-H)(μ-dppf)(μ3-η1:η2:η2-MeCHC≡CEt)] (2) results via aliphatic C–H bond activation of one of the ethyl groups. With diphenylacetylene, the major product is [Ru3(CO)6(μ-H){μ-Ph2P(C5H3)Fe(C5H4)PPh2}(μ3-η1:η1:η2-PhC2Ph)] (3) which contains a capping alkyne ligand and a metalated dppf ligand, formed via C–H activation of one of the cyclopentadienyl rings. Metalation results in formation of a dative Fe–Ru bond. With activated alkynes (RCO2)C2(CO2R) (R = Me, Et), alkyne coupling occurs to afford the open 52-electron clusters [Ru3(μ-CO)(CO)6(μ-PPh2){μ-η1:κ1-Ph2P(C5H4)Fe(C5H4)}{μ3-η1:η2:η2:κ1-C4(CO2R)4}] (4–5). The later contain bridging phosphido (PPh2) and chelating Ph2PFe(C5H4)2 ligands, formed via a previously unreported P–C bond cleavage of the coordinated dppf ligand. All four new clusters have been characterized by single-crystal X-ray diffraction studies. We discuss likely reaction pathways and why these transformations differ so much as a function of the appended diphosphine ligand.