ORGANO-F-ELEMENT THERMOCHEMISTRY - ACTINIDE GROUP-14 ELEMENT AND ACTINIDE TRANSITION-ELEMENT BOND DISRUPTION ENTHALPIES AND STOICHIOMETRIC CATALYTIC CHEMICAL IMPLICATIONS THEREOF IN HETEROBIMETALLIC TRIS(CYCLOPENTADIENYL)URANIUM(IV) COMPOUNDS

Uranium-metal bond disruption enthalpies have been determined in the series of complexes Cp3U-MPh3, where Cp = eta-5-C5H5, Ph = C6H5, and M = Si, Ge, Sn, and in Cp3U-M'(CO)2Cp, where M' = Fe, Ru. Thermochemical data were obtained by anaerobic batch-titration solution calorimetry in toluene from enthalpies of solution and iodinolysis of the aforementioned compounds. Derived U-M/U-M' bond disruption enthalpies in toluene solution are as follows (M/M' moiety, kcal/mol): SiPh3, 37.3 (4.2); GePh3, 38.9 (4.5); SnPh3, 37.2 (4.0); Fe(CO)2Cp, 30.9 (3.0); Ru(CO)2Cp, 40.4 (4.0). These data fall in a relatively narrow range and indicate comparatively weak heterobimetallic bonding. Chemical implications of the present thermochemical results include the general favorability and marked M/M' sensitivity of alkane, hydrogen, and amine elimination synthetic routes to these compounds, the existence of favorable pathways for hydrocarbon and olefin activation, and the observation that no steps in plausible f-element-catalyzed dehydrogenative silane polymerization and olefin hydrosilylation cycles are predicted to have major thermodynamic impediments.