Synthesis and Comparative η¹-Alkyl and Sterically Induced Reduction Reactivity of (C₅Me₅)₃Ln Complexes of La, Ce, Pr, Nd, and Sm

Abstract

The synthesis of (C 5 Me 5 ) 3 Ce and (C 5 Me 5 ) 3 Pr from [(C 5 Me 5 ) 2 Ln][(μ-Ph) 2 BPh 2 ] and KC 5 Me 5 completes the series of sterically crowded (C 5 Me 5 ) 3 Ln 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 (C 5 Me 5 ) 3 Ln complexes required silylated glassware, which surprisingly was not necessary for the more sterically crowded analogues. (C 5 Me 5 ) 3 Ce and (C 5 Me 5 ) 3 Pr display longer Ln−C(C 5 Me 5 ) distances than any previously described Ce or Pr complexes containing the (C 5 Me 5 ) - ligand. The η 1 -C 5 Me 5 alkyl-like reactivity of the (C 5 Me 5 ) 3 Ln complexes was investigated with CO, ethylene, THF, and H 2 . The sterically induced reduction (SIR) reactivity of the (C 5 Me 5 ) 3 Ln complexes was examined with Se PPh 3, AgBPh 4, C 8 H 8, and phenazine. All of these data indicate that (C 5 Me 5 ) 3 Ln reactivity increases with decreasing size of the metal and hence increased steric crowding. The reactivity of (C 5 Me 5 ) 3 Ln with CO 2 and with Et 3 NHBPh 4 was examined since each substrate could react by either η 1 -C 5 Me 5 alkyl or SIR pathways. In both cases, alkyl-like reactivity is observed: CO 2 forms the insertion product (C 5 Me 5 ) 2 Ln(O 2 CC 5 Me 5 ), containing a carboxylate with a pentamethylcyclopentadiene substituent, and Et 3 NHBPh 4 forms [(C 5 Me 5 ) 2 Ln][(μ-Ph) 2 BPh 2 ] and C 5 Me 5 H. The reactions of (C 5 Me 5 ) 3 Sm with aryl halides and primary alkyl halide radical clocks (RX) yield C 5 Me 5 R, C 5 Me 5 X, (C 5 Me 5 ) 2, R−R, and [(C 5 Me 5 ) x SmX y ] z as products, which indicate that SIR is not the only reaction pathway with these substrates. The X-ray crystal structures of the (C 5 Me 5 ) 3 Ln reaction products [(C 5 Me 5 ) 2 La] 2 (μ - η 2:η 2 -Se 2 ), [(C 5 Me 5 ) 2 (THF)La] 2 (μ - η 2:η 2 -Se 2 ), [(C 5 Me 5 ) 2 La] 2 (μ-η 3:η 3 -C 12 N 2 H 8 ), [(C 5 Me 5 ) 2 Sm(μ-I)] 3, and (C 5 Me 5 ) 2 Sm(O 2 CC 5 Me 5 ) are described as well as a new synthesis of (C 5 Me 5 ) 3 Sm from (C 5 Me 5 ) 2 Sm and (C 5 Me 5 ) 2 .