Synthesis, Structural Characterization, and Reactivity of Organolanthanide Complexes Derived from a New, Versatile Boron-Bridged Ligand, iPr2NB(C9H7)(C2B10H11)

Abstract

New boron-bridged ligands incorporating both indenyl and carboranyl moieties have been prepared. Reaction of iPr2NB(C9H7)Cl with 1 equiv of Li2C2B10H10 gave, after treatment with 1 equiv of n-BuLi, the dilithium salt [iPr2NB(C9H6)(C2B10H10)]Li2(OEt2)2 (1), which was conveniently converted into its neutral counterpart iPr2NB(C9H7)(C2B10H11) (2) via reaction with excess C5H6. Mixing 1 and 2 in a 1:1 molar ratio quantitatively afforded the monolithium salt [iPr2NB(C9H6)(C2B10H11)]Li(THF)2 (3). Treatment of LnI2 with 1 equiv of 1 generated the trivalent organolanthanide complexes meso-[{η5:σ-iPr2NB(C9H6)(C2B10H10)}2Ln][Li(S)n] (Ln = Sm, Yb; S = THF, n = 4; S = DME, n = 3), which was also prepared in a much higher yield by reaction of LnI2 with 1 equiv of 1 followed by treatment with 1 equiv of 3. Both inter- and intramolecular electron-transfer pathways are proposed for these reactions. Reaction of LnCl3 with 1 or 2 equiv of 1 gave the same ionic complexes meso-[{η5:σ-iPr2NB(C9H6)(C2B10H10)}2Ln][Li(S)n] (Ln = Nd, Y, Yb; S = THF, n = 4; S = DME, n = 3). Silylamine elimination reactions of 2 and Ln[N(SiHMe2)2]3(THF)2 resulted in clear formation of [η5:σ-iPr2NB(C9H6)(C2B10H10)]LnN(SiHMe2)2(THF)2 (Ln = Nd (8), Er (9), Y (10)). Treatment of 8 with Me3NHCl or Me3SiCl led to the isolation of 2 and NdCl3(DME)2 (11), respectively. The new complexes were fully characterized by various spectroscopic data and element analyses. Some were further confirmed by single-crystal X-ray analyses. Complex 8 is an active catalyst for the polymerization of methyl methacrylate (MMA) in toluene, affording syn-rich poly(MMA)s.