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

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journal contribution
posted on 29.11.2001, 00:00 by William J. Evans, Dimitrios G. Giarikos, Joseph W. Ziller
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.