Organoruthenium thermochemistry. Enthalpies of reaction of (Cp*RuCl)4 and Cp*Ru(COD)Cl (Cp* = .eta.5-C5Me5, COD = cyclooctadiene) with dienes and tertiary phosphine ligands

Abstract

The enthalpies of reaction of Cp*Ru(COD)Cl(Cp* = eta5-C5Me5, COD = cyclooctadiene) with a series of monodentate ligands, leading to the formation of Cp*Ru(ER3)2Cl (E = P, As), have been measured by anaerobic solution calorimetry in THF at 30-degrees-C. The enthalpies of reaction associated with the rapid and quantitative reaction of the (Cp*RuCl)4 complex with diene ligands in THF at 30-degrees-C, producing Cp*Ru(diene)CI complexes, have also been investigated. Reaction of (Cp*RuCl)4 with excess phosphine ligand, at 30-degrees-C, has been shown to quantitatively yield the corresponding Cp*Ru(PR3)2Cl complex and allows for the design of a thermochemical cycle assuring the internal consistency of the thermochemical data. The overall relative order of stability established for the preceding complexes is as follows: for monodentate ligands, AsEt3 < PPh3 < PnBu3 < PEt3 < PPh2Me < P(OPh)3 < PPhMe2 < PMe3 < P(OMe)3; for dienes, 2,3-dimethyl-1,3-butadiene < 1,3-cyclohexadiene < cyclooctadiene < 1,3-pentadiene < norbornadiene. Comparisons with other organometallic systems and insight into factors influencing the Ru-L bond disruption enthalpies are discussed.