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 = η⁵-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.