Tris(boratabenzene) Lanthanum Complexes: Synthesis, Structure, and Reactivity

A series of tris­(boratabenzene) lanthanum complexes were synthesized and structurally characterized. Salt elimination of anhydrous LaCl₃ with Li­[C₅H₅BR] (R = H, NEt₂) provided tris­(boratabenzene) lanthanum complexes [C₅H₅BH]₃­LaLiCl (1) and [C₅H₅BNEt₂]₃­LaLiCl­(THF) (2) in high yields. Hydroboration of 1-hexene or 3-hexyne with 1 gave the alkyl- or alkenyl-functionalized boratabenzene lanthanum complexes, [C₅H₅B­(CH₂)₅CH₃]₃­LaLiCl­(THF) (3) and [C₅H₅BC­(C₂H₅)CH­(C₂H₅)]₃­LaLiCl­(THF) (4), in good yields. Hydroboration of N,N′-diisopropylcarbodiimide with 1 gave the monohydroboration product [C₅H₅BN­(ⁱPr)­CHN­(ⁱPr)]­[C₅H₅BH]₂La (5) due to the steric bulk of the [C₅H₅BN­(ⁱPr)­CHN­(ⁱPr)]⁻ ligand. Complex 5 can undergo further hydroboration with 3-hexyne or dehydrogenative coupling with phenyl acetylene to afford [C₅H₅BN­(ⁱPr)­CHN­(ⁱPr)]­[C₅H₅BC­(C₂H₅)CH­(C₂H₅)]₂La (6) or [C₅H₅BN­(ⁱPr)­CHN­(ⁱPr)]­[C₅H₅BCCPh)]₂La (7).