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[O 2 CC(CH 3 ) 2 CH 2 CH 3 ] 3 } x ( 1 ) and {La[O 2 CC(CH 3 ) 2 CH 2 CH 3 ] 3 } x ( 2 ) were synthesized from the lanthanide metal and 2,2-dimethylbutyric acid in the presence of a catalytic amount of HgCl 2 and Hg(OAc) 2 . Nd 2 [O 2 CCH(C 6 H 5 )CH 2 CH 3 ] 6 [HO 2 CCH(C 6 H 5 )CH 2 CH 3 ] 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 [O 2 CC(CH 3 ) 2 CH 2 CH 3 ] 6 [pyridine] 4 ( 4 ) and La 2 [O 2 CC(CH 3 ) 2 CH 2 CH 3 ] 6 [pyridine] 4 ( 5 ). 3 crystallizes from hexanes as the carboxylic acid adduct. 1 and 2 react with Et 2 AlCl to form the isolable solids 6 and 7, which react with Al( i Bu) 3 to generate catalytically active systems which polymerize isoprene, ethylene, and styrene. Although crystallization of 6 from THF forms NdCl 3 (THF) 4 ( 8 ) and crystallization of 7 from pyridine forms [LaCl 3 (pyridine) 4 ] 2 ( 9 ), complexes 6 and 7 are not simply LnCl 3, since elemental analyses show that they contain aluminum.