Synthesis and Comparative η1-Alkyl and Sterically Induced Reduction Reactivity of (C5Me5)3Ln Complexes of La, Ce, Pr, Nd, and Sm
The synthesis of (C5Me5)3Ce and (C5Me5)3Pr from [(C5Me5)2Ln][(μ-Ph)2BPh2] and KC5Me5 completes the series of sterically crowded (C5Me5)3Ln complexes for the larger lanthanides, La−Nd and Sm, and allows a comparison of structure and reactivity as a function of metal size. Synthesis of these new (C5Me5)3Ln complexes required silylated glassware, which surprisingly was not necessary for the more sterically crowded analogues. (C5Me5)3Ce and (C5Me5)3Pr display longer Ln−C(C5Me5) distances than any previously described Ce or Pr complexes containing the (C5Me5)- ligand. The η1-C5Me5 alkyl-like reactivity of the (C5Me5)3Ln complexes was investigated with CO, ethylene, THF, and H2. The sterically induced reduction (SIR) reactivity of the (C5Me5)3Ln complexes was examined with SePPh3, AgBPh4, C8H8, and phenazine. All of these data indicate that (C5Me5)3Ln reactivity increases with decreasing size of the metal and hence increased steric crowding. The reactivity of (C5Me5)3Ln with CO2 and with Et3NHBPh4 was examined since each substrate could react by either η1-C5Me5 alkyl or SIR pathways. In both cases, alkyl-like reactivity is observed: CO2 forms the insertion product (C5Me5)2Ln(O2CC5Me5), containing a carboxylate with a pentamethylcyclopentadiene substituent, and Et3NHBPh4 forms [(C5Me5)2Ln][(μ-Ph)2BPh2] and C5Me5H. The reactions of (C5Me5)3Sm with aryl halides and primary alkyl halide radical clocks (RX) yield C5Me5R, C5Me5X, (C5Me5)2, R−R, and [(C5Me5)xSmXy]z as products, which indicate that SIR is not the only reaction pathway with these substrates. The X-ray crystal structures of the (C5Me5)3Ln reaction products [(C5Me5)2La]2(μ-η2:η2-Se2), [(C5Me5)2(THF)La]2(μ-η2:η2-Se2), [(C5Me5)2La]2(μ-η3:η3-C12N2H8), [(C5Me5)2Sm(μ-I)]3, and (C5Me5)2Sm(O2CC5Me5) are described as well as a new synthesis of (C5Me5)3Sm from (C5Me5)2Sm and (C5Me5)2.
Evans, William J.; Perotti, Jeremy M.; Kozimor, Stosh A.; Champagne, Timothy M.; Davis, Benjamin L.; Nyce, Gregory W.; Fujimoto, Cy H.; Clark, Robert D.; Johnston, Matthew A.; and Ziller, Joseph W., "Synthesis and Comparative η1-Alkyl and Sterically Induced Reduction Reactivity of (C5Me5)3Ln Complexes of La, Ce, Pr, Nd, and Sm" (2005). Chemistry and Physics Faculty Articles. 94.