ORGANORUTHENIUM THERMOCHEMISTRY - ABSOLUTE METAL-LIGAND BOND DISRUPTION ENTHALPIES IN THE (ETA(5)-C(5)ME(5))(CO)(2)RU-X SYSTEM (X=H, CL, BR, I) AND THERMODYNAMIC INFLUENCES OF ANCILLARY LIGAND VARIATION ON THERU-X BOND DISRUPTION ENTHALPY

The enthalpies of reaction of (eta(5)-C(5)Me(5))(CO)(2)RU-H (1) With C Cl4, 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 calor imetry 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/mo l), an absolute Ru-X bond disruption enthalpy (BDE) scale can be estab lished for ruthenium halide complexes. The absolute BDE scale for ruth enium 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 rut henium BDE values can be directly compared with other metal-based syst ems and lead to a clearer understanding of general BDE trends in M-X s ystems. In addition, a number of enthalpies of reaction were measured involving organoruthenium hydride complexes with varied ancillary liga nds in order to examine the ancillary ligand effects on the relative R u-X bond enthalpies.