SOLUTION THERMOCHEMICAL STUDY OF TERTIARY PHOSPHINE LIGAND SUBSTITUTION-REACTIONS IN THE RHCL(CO)(PR(3))(2) SYSTEM

The enthalpies of reaction of [Rh(CO)(2)Cl](2) (1) with a series of mo nodentate tertiary phosphine ligands, leading to the formation of RhCl (CO)(PR(3))(2) complexes, have been measured by anaerobic solution cal orimetry in CH2Cl2 at 30.0 degrees C. These reactions are rapid and qu antitative. The measured reaction enthalpies span a range of 43 kcal/m ol. The relative stability scale established is as follows: P(NC4H4)(3 ) < P(NC4H4)(2)(C6H5) < P(OPh)(3) < P(p-CF3C6H4)(3) < P(NC4H4)(C6H5)(2 ) < P(p-ClC6H4)(3) < AsEt(3) < P(p-FC6H4)(3) < PPh(3) < P(p-CH3C6H4)(3 ) < P(p-CH3OC6H4)(3) < PPh(2)Me < P(OMe)(3) < PPhMe(2) < PEt(3). The r elative importance of phosphine electronic ligand parameters is closel y examined in terms of the presented quantitative thermochemical infor mation. Comparisons with enthalpy data in related organometallic syste ms are also presented.