The enthalpies of reaction of (PPh3)2Cl2Ru=CH-CH=CPh2 (1) with a series of tertiary phosphine ligands, leading to the formation of (PR3)2Cl2Ru=CH-CH=CPh2 complexes (PR3 = PiPr3, PBz3, PPh2Cy, PPhCy2, PCy3, and PiBu3) have been measured by solution calorimetry in CH2Cl2 at 30 °C. The range of reaction enthalpies spans some 6.5 kcal/mol and helps to establish a relative order of complex stability for these six ruthenium carbene complexes. The enthalpies of reaction for tertiary phosphine complexes, trans-(PR3)2Cl2Ru=CH-CH= CPh2, are as follows (PR3, kcal/mol): PPh3, 0; PBz3, -1.3 (0.2); PCyPh2, -1.8 (0.2); PCy2Ph, -3.8 (0.2); PiBu3, -3.8 (0.2); PiPr3, -5.2 (0.1); PCy3, -6.5 (0.3). The thermodynamics of the exchange of these sterically demanding tertiary phosphine ligands for PPh3 in 1 provides a measurement of the relative importance of phosphine steric and electronic properties/ character to the enthalpy of reaction in this system. Correlations of various factors gauging the electron-donating properties of the phosphine ligands clearly show the electronic factor to be the overwhelming contributor to the enthalpy of reaction in this system.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry