Unsolvated Lanthanide Metallocene Cations [(C₅Me₅)₂Ln][BPh₄]:  Multiple Syntheses, Structural Characterization, and Reactivity Including the Formation of (C₅Me₅)₃Nd¹

Divalent (C₅Me₅)₂Sm reacts with AgBPh₄ in toluene to form [(C₅Me₅)₂Sm][BPh₄], 1, in ca. 60% yield. The solid-state structure of 1 consists of a trivalent (C₅Me₅)₂Sm bent metallocene unit with a 2.702(3) Å average Sm−C(C₅Me₅) distance that is oriented toward two of the phenyl rings of the [BPh₄]^- anion with 2.825(3) and 2.917(3) Å Sm−C(o-Ph) distances. 1 can also be obtained from reactions of Et₃NHBPh₄ in arene solvents with the trivalent samarium precursors (C₅Me₅)₂Sm[CH(SiMe₃)₂] (>50% yield) and (C₅Me₅)₂Sm(η³-CH₂CHCH₂) (2) (>95% yield). 1 reacts with LiCH(SiMe₃)₂ in benzene to produce (C₅Me₅)₂Sm[CH(SiMe₃)₂] in over 95% yield. The reaction of 1 with KC₅Me₅ in benzene constitutes a new synthesis of the sterically crowded complex (C₅Me₅)₃Sm, which is formed in over 90% yield. This reaction provides a convenient way to make (C₅Me₅)₃Ln complexes with lanthanides which do not have a reactive divalent oxidation state. To enhance the ease of preparing (C₅Me₅)₃Ln complexes from LnCl₃, an improved synthesis of the allyl precursors (C₅Me₅)₂Ln(η³-CH₂CHCH₂) (Ln = Sm (2), Nd (3), Tm (4)) is reported. 2−4 can be prepared in 60−90% yield from (C₅Me₅)₂LnCl₂K(THF)₂ and ClMg(CH₂CHCH₂) followed by desolvation of the solids between 55 and 70 °C for 4−16 h. 2−4 react with Et₃NHBPh₄ in benzene to produce [(C₅Me₅)₂Ln][BPh₄] (Ln = Sm (1), Nd (5), Tm (6)). 5 has a solid-state structure identical to that of 1 and similarly reacts with LiCH(SiMe₃)₂ and KC₅Me₅ in benzene to produce (C₅Me₅)₂Nd[CH(SiMe₃)₂] and (C₅Me₅)₃Nd (7), respectively, in high yield. 7 was characterized by X-ray crystallography and shown to have an (η⁵-C₅Me₅)₃Nd structure with a 2.86(6) Å Nd−C(C₅Me₅) distance. Since the allyl complexes (C₅Me₅)₂Ln(η³-CH₂CHCH₂) are readily converted to the hydrides [(C₅Me₅)₂LnH]_n by hydrogen, the improved synthesis of the allyl complexes also provides an improved route to these hydrides as demonstrated by the reaction of (C₅Me₅)₂Nd(η³-CH₂CHCH₂) with H₂ to form [(C₅Me₅)₂NdH]₂ in 75% yield.