Lanthanide Carboxylate Precursors for Diene Polymerization Catalysis:  Syntheses, Structures, and Reactivity with Et₂AlCl

Synthetic, structural, and reactivity results are presented on neodymium and lanthanum carboxylates that can function as models for diene polymerization catalysts. The neodymium and lanthanum carboxylates {Nd[O₂CC(CH₃)₂CH₂CH₃]₃}_x (1) and {La[O₂CC(CH₃)₂CH₂CH₃]₃}_x (2) were synthesized from the lanthanide metal and 2,2-dimethylbutyric acid in the presence of a catalytic amount of HgCl₂ and Hg(OAc)₂. Nd₂[O₂CCH(C₆H₅)CH₂CH₃]₆[HO₂CCH(C₆H₅)CH₂CH₃]₄ (3) was prepared similarly from neodymium powder and 2-phenylbutyric acid. 1 and 2 crystallize from hot pyridine as the dimeric pyridine adducts Nd₂[O₂CC(CH₃)₂CH₂CH₃]₆[pyridine]₄ (4) and La₂[O₂CC(CH₃)₂CH₂CH₃]₆[pyridine]₄ (5). 3 crystallizes from hexanes as the carboxylic acid adduct. 1 and 2 react with Et₂AlCl to form the isolable solids 6 and 7, which react with Al(ⁱBu)₃ to generate catalytically active systems which polymerize isoprene, ethylene, and styrene. Although crystallization of 6 from THF forms NdCl₃(THF)₄ (8) and crystallization of 7 from pyridine forms [LaCl₃(pyridine)₄]₂ (9), complexes 6 and 7 are not simply LnCl₃, since elemental analyses show that they contain aluminum.