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 SePPh3, 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.以[(C₅Me₅)₂Ln][(μ-苯基)₂BPh₂]与五甲基环戊二烯钾（KC₅Me₅）为原料合成(C₅Me₅)₃Ce与(C₅Me₅)₃Pr，完成了大尺寸镧系元素（La至Nd以及Sm）的位阻型(C₅Me₅)₃Ln配合物系列，从而可基于金属离子尺寸差异对比其结构与反应活性。这类新型(C₅Me₅)₃Ln配合物的合成需使用硅烷化处理的玻璃仪器，而令人意外的是，位阻更大的同类配合物的合成却无需该操作。 (C₅Me₅)₃Ce与(C₅Me₅)₃Pr的Ln−C(C₅Me₅)键长均长于此前已报道的所有含(C₅Me₅)⁻配体的Ce或Pr配合物。针对(C₅Me₅)₃Ln配合物的η¹-五甲基环戊二烯基类烷基反应活性，我们以一氧化碳（CO）、乙烯、四氢呋喃（THF）及氢气（H₂）为底物开展了研究。以硒代三苯基膦（Se=PPh₃）、四苯硼化银（AgBPh₄）、环辛四烯（C₈H₈）及吩嗪为底物，考察了(C₅Me₅)₃Ln配合物的空间诱导还原（Sterically Induced Reduction, SIR）反应活性。 所有实验数据均表明，(C₅Me₅)₃Ln配合物的反应活性随金属离子尺寸减小、空间位阻增大而提升。我们还考察了(C₅Me₅)₃Ln与二氧化碳（CO₂）及三乙胺四苯硼酸盐（Et₃NHBPh₄）的反应，这两类底物均可通过η¹-五甲基环戊二烯基类烷基反应或SIR路径发生转化。两类反应均表现出类烷基反应特征：CO₂插入生成产物(C₅Me₅)₂Ln(O₂CC₅Me₅)，该产物含有带五甲基环戊二烯基取代基的羧酸酯基团；Et₃NHBPh₄则反应生成[(C₅Me₅)₂Ln][(μ-Ph)₂BPh₂]与五甲基环戊二烯（C₅Me₅H）。 (C₅Me₅)₃Sm与芳基卤化物、一级烷基卤化物自由基钟（RX）的反应产物包括C₅Me₅R、C₅Me₅X、(C₅Me₅)₂、R−R以及[(C₅Me₅)ₓSmXᵧ]ₙ，这表明SIR并非该类底物的唯一反应路径。本文还报道了(C₅Me₅)₃Ln配合物反应产物的X射线晶体结构，包括[(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以及(C₅Me₅)₂Sm(O₂CC₅Me₅)；同时还报道了以(C₅Me₅)₂Sm与(C₅Me₅)₂为原料合成(C₅Me₅)₃Sm的新方法。