Organo-f-Element Thermochemistry. Absolute Metal-Ligand Bond Disruption Enthalpies in Bis(pentamethylcyclopentadienyl)samarium Hydrocarbyl, Hydride, Dialkylamide, Alkoxide, Halide, Thiolate, and Phosphide Complexes. Implications for Organolanthanide Bonding and Reactivity

Article abstract of DOI:10.1021/ja00202a027

Absolute samarium-ligand bond disruption enthalpies in the series Cp'2Sm-R/X (Cp' = η⁵-(CH3)5C5) have been measured by iodinolytic and alcoholytic isoperibol titration calorimetry of Cp'2Sm/(Cp'2Sm-I)_n, (Cp'2Sm-O-t-Bu)2/Cp'2Sm-R/X ensembles in toluene.Derived D(Cp'2Sm-R/X) values in toluene solution are as follows (kcal/mol, R/X): 47.0 (1.5), CH(SiMe3)2; 45.0 (1.5), η³-C3H5; 93.2, CCPh; 54.2 (3.0), H; 48.2 (1.8), NMe2; 82.4 (3.5), O-t-Bu; 81.3 (1.0), OCH(t-Bu)2; 97.1 (3.0), Cl; 83.6 (1.5), Br; 69.4 (2.4), I; 73.4 (2.4), S-n-Pr; 32.6 (2.0), PEt2.D(Cp'2Sm-THF)and D(Cp'2Sm(THF)-THF) values were also determined in toluene and are 7.3 (0.4) and 4.9 (1.0) kcal/mol, respectively, while D(Cp'2Sm(THF)-I) was found to be 72.7 (2.9) kcal/mol.The observed D(Sm-halogen) parameters are close to the D₁ values of the corresponding samarium trihalides.Important trends in D(Cp'2Sm-R/X) include a relatively small value of D(Sm-H) - D(Sm-alkyl), a large value of D(Sm-I) - D(Sm-alkyl), and generally strong bonds to group 15 and group 16 ligands.A variety of Sm-centered ligand transposition and oxidative addition/reductive elimination processes are analyzed in light of the present data.The formation of strong Sm-heteroelement bonds makes an important contribution to the driving force.Hydrocarbon functionalization via dinuclear Sm(II) -> Sm(III) oxidative addition processes is only expected to be exothermic in special cases.