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

The enthalpies of reaction of ((p-cymene)RuCl2)(2) (p-cymene = (CH3)(2 )CH(C)6H(4)CH(3)) with a series of tertiary phosphine ligands, leading to the formation of (p-cymene)RuCl2(PR(3)) complexes (PR(3) = tertiar y phosphine) have been measured by solution calorimetry in CH2-Cl-2 at 30 degrees C. The range of reaction enthalpies spans some 22 kcal/mol . The overall relative order of stability established is as follows (P R(3);-Delta H, kcal/mol): P(p-CF3C6H4)(3) < PCy(3) < PCy(2)Ph < P(p-Cl C6H4)(3) < P(OPh)(3) < (PPr3)-Pr-i < PPh(3) < P(P-FC6H4)(3) < P(P-CH3C 6H4)(3) < PCyPh(2) < P(P-CH3OC6H4)(3) < P(i)Bu(3) < PBz(3) < PPh(2)Et < PPh(2)Me < P(OMe)(3) < PEt(3) < PPhMe(2) < PMe(3). A quantitative an alysis of ligand effect of the present data helps clarify the exact st eric versus electronic ligand contributions to the enthalpy of reactio n in this system. Both steric and electronic factors appear to play an important role in dictating the magnitude of the enthalpy of reaction .