Enthalpies of reaction of ((p-cymene)RuCl2)2 with monodentate tertiary phosphine ligands. Importance of both steric and electronic ligand factors in a ruthenium(II) system

Article abstract of DOI:10.1021/om00010a027

The enthalpies of reaction of ((p-cymene)RuCl₂)₂ (p-cymene = (CH₃)₂CHC₆H₄CH₃) with a series of tertiary phosphine ligands, leading to the formation of (p-cymene)RuCl₂(PR₃) complexes (PR₃ = tertiary phosphine) have been measured by solution calorimetry in CH₂Cl₂ at 30°C. The range of reaction enthalpies spans some 22 kcal/mol. The overall relative order of stability established is as follows (PR₃; - ΔH, kcal/mol): P(p-CF₃C₆H₄)₃ < PCy₃ < PCy₂Ph < P(p-ClC₆H₄)₃ < P(OPh)₃ < PⁱPr₃ < PPh₃ < P(p-FC₆H₄)₃ < P(p-CH₃C₆H₄)₃ < PCyPh₂ < P(p-CH₃OC₆H₄)₃ < PⁱBu₃ < PBz₃ < PPh₂Et < PPh₂Me < P(OMe)₃ < PEt₃ < PPhMe₂ < PMe₃. A quantitative analysis of ligand effect of the present data helps clarify the exact steric versus electronic ligand contributions to the enthalpy of reaction in this system. Both steric and electronic factors appear to play an important role in dictating the magnitude of the enthalpy of reaction.