Organoruthenium Thermochemistry. Absolute Metal-Ligand Bond Disruption Enthalpies in the (.eta.5-C5Me5)(CO)2Ru-X System (X = H, Cl, Br, I) and Thermodynamic Influences of Ancillary Ligand Variation on the Ru-X Bond Disruption Enthalpy

Abstract

The enthalpies of reaction of (eta(5)-C(5)Me(5))(CO)(2)RU-H (1) With CCl4, CBr4, and CH3I leading to the formation of (eta(5)-C(5)Me(5))(CO)(2)Ru-X complexes (X = Cl, Br, I) have been measured by solution calorimetry in THF at 30 degrees C. On the basis of enthalpies of reaction and the recently reported Ru-H in (C5H5)Ru(CO)(2)H (65 +/- 1.0 kcal/mol), an absolute Ru-X bond disruption enthalpy (BDE) scale can be established for ruthenium halide complexes. The absolute BDE scale for ruthenium halide complexes, (eta(5)-C(5)Me(5))(CO)(2)RU-X, is as follows (X, kcal/mol): Cl, 80.7; Br, 61.1; and I, 55.6, respectively. These ruthenium BDE values can be directly compared with other metal-based systems and lead to a clearer understanding of general BDE trends in M-X systems. In addition, a number of enthalpies of reaction were measured involving organoruthenium hydride complexes with varied ancillary ligands in order to examine the ancillary ligand effects on the relative Ru-X bond enthalpies.