Ruthenium Carboxylate Complexes as Probes to Metal Ligand Interactions

A synthetic route to [Ru(κ2-O₂CC₆H₄-R)2(PPh₃)₂] complexes (where R= 4-F, 4-CH3, 4-OMe, 4-NMe2, 3-F, 3-CH3, 3-OMe, 3-NMe2) has been developed. From these species, novel ruthenium-carbonyl [Ru(κ2-O₂CC₆H₄-R)(κ1-O₂CC₆H₄-R)(CO)(PPh₃)₂] (where R= 4-F,4-CH3,4-OMe,4-NMe2,3-F,3-CH3,3-NMe2), and vinylidene complexes [Ru(κ2-O₂CC₆H₄-R)(κ1-O₂CC₆H₄-R)(=C=HPh)(PPh₃)₂] (where R= 4-F,4-CH3,4-OMe,4-NMe2,3-F,3-CH3,3-NMe2), have been synthesised.
Hammett studies have shown the effect of changing the substituent on the carboxylate ligand on the M-C π-back bonding for the complexes of the general type [Ru(κ2-O₂CC₆H₄-R)(κ1-O₂CC₆H₄-R)(CO)(PPh₃)₂] and [Ru(κ2-O₂CC₆H₄-R)(κ1-O₂CC₆H₄-R)(=C=HPh)(PPh₃)₂]. The CO stretching frequencies in the IR spectra of the complexes [Ru(κ2-O₂CC₆H₄-R)(κ1-O₂CC₆H₄-R)(CO)(PPh₃)₂] demonstrate the more electron-donating substituents strengthen the bonding between the metal and the carbonyl ligand. A similar trend is observed in the case of the vinylidene-containing ruthenium complexes, demonstrating that the electronic properties of the ancillary ligands may profoundly affect the metal-vinylidene interaction.