Homolysis of the Eu−N Bond. Synthesis, Structural Characterization, and Catalytic Activity of Novel Europium(II) Complexes

Two new indene compounds, C 9 H 7 CH 2 SiMe 2 NC 4 H 8 ( 1 ) and C 9 H 6 -1-Me-3-CH 2 SiMe 2 NC 4 H 8 ( 2 ), were synthesized by the reaction of C 9 H 6 RLi (R = H, Me) with ClCH 2 SiMe 2 Cl, followed by treatment with lithium pyrrolidinide C 4 H 8 NLi. The interaction of [(Me 3 Si) 2 N] 3 Eu(μ-Cl)Li(THF) 3 with 2 equiv of 1 in refluxing toluene produced, after workup, a novel triple-decker sandwich tetranuclear europium(II) compound, [{ η: 5 η: 5 η 1 -(C 9 H 5 CH 2 SiMe 2 NC 4 H 8 ) 2 }Eu 2 ( μ -Cl)] 2 [ μ - η 3: η 5: η 1: η 3: η 5: η 1 -(C 9 H 5 CH 2 SiMe 2 NC 4 H 8 ) 2 ]·C 7 H 8 ·(C 6 H 6 ) 0.5 ( 3 ), with a coupled indenyl ligand through tandem silylamine elimination, reduction of Eu 3+ to Eu 2+, and the C−C coupling reactions. To probe the formation pathway of complex 3, the interaction of C 9 H 6 -1-Me-3-CH 2 SiMe 2 NC 4 H 8 ( 3 ) with [(Me 3 Si) 2 N] 3 Eu(μ-Cl)Li(THF) 3 was studied. Treatment of [(Me 3 Si) 2 N] 3 Eu(μ-Cl)Li(THF) 3 with 2 equiv of 2 in refluxing toluene temperature or at 60 °C produced, after workup, a monomeric europium(II) complex, ( η 5: η 1 -C 9 H 5 -1-Me-3-CH 2 SiMe 2 NC 4 H 8 ) 2 Eu ( 4 ), via tandem silylamine elimination/homolysis of the Eu−N bond reactions. The formation pathway for complex 3 was proposed. All the compounds were fully characterized by spectroscopic methods and elemental analyses, and the structures of complexes 3 and 4 were additionally determined by single-crystal X-ray diffraction analyses. It was found that complexes 3 and 4 can function as single-component MMA polymerization initiators, which represent the first examples of europium(II) complexes as single-component MMA polymerization catalysts. The solvents and temperature effects' on the activities of the catalysts were also discussed.