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)(2)CH2CH3](3)}(x) (1) and {La[O2CC(CH3)(2)CH2CH3](3)}(x) (2) were synthesised from the lanthanide metal and 2,2-dimethylbutyric acid in the presence of a catalytic amount of HgCl2 and Hg(OAc)(2). Nd-2[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 Nd-2[O2CC(CH3)(2)CH2CH3](6)[pyridine](4) (4) and La-2[O2CC(CH3)(2)CH2CH3](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(Bu-i)(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 LnCl(3), since elemental analyses show that they contain aluminum.