Enthalpies of reaction of ruthenium complex Cp*Ru(COD)Cl (Cp* = .eta.5-C5Me5; COD = cyclooctadiene) with chelating tertiary phosphine ligands. Solution thermochemical investigation of ligand substitution and ring strain energies in Cp*Ru(PP)Cl complexes

Abstract

The enthalpies of reaction of CpRu(COD)Cl (Cp = eta(5)-C5H5; COD = eta(4)-cyclooctadiene) with a series of bidentate ligands, leading to the formation of CpRu(PP)Cl complexes, have been measured by anaerobic solution calorimetry in THF at 30.0 degrees C. The overall relative order of stability established for these complexes is as follows: dppm < dmpm < dppb < dppe < dppp < dppv < depe < dmpe. Comparison between enthalpies of these reactions and those of monodentate phosphine ligands affords a quantitative treatment of ring strain enthalpies in these organoruthenium metallacyclic compounds. Significant ring strain energy is displayed in the four-membered metallacycle and is on the order of 13 kcal/mol. A single crystal X-ray diffraction study has been performed on one of the new complexes, CpRu(dppv)Cl [dppv = bis(diphenylphosphino)ethylene] (C31H27ClP2Ru.CH2Cl2, P1, a 10.344(2) Angstrom, b = 11.907(2) Angstrom, c 13.183(1) Angstrom, alpha 67.89(1)degrees, beta 76.52(1)degrees, gamma = 85.96(2)degrees, V = 1462.5(5) Angstrom(3), and Z = 2). Comparisons of the thermochemical data with the C(5)Me(5)-based system and related metallacyclic complexes are also presented.