The reactions of (C 5 Me 5 ) 2 Ln(THF) 2 with 1 equiv of KCH(SiMe 3 ) 2 in THF afforded the corresponding Ln(II) alkyl complexes [(C 5 Me 5 )Ln(CH(SiMe 3 ) 2 )(C 5 Me 5 )K(THF) 2 ] n (Ln = Sm ( 1a ), Eu ( 1b ), Yb ( 1c )) in 90−92% isolated yields. In the presence of PhSiH 3 the reactions of (C 5 Me 5 ) 2 Ln(THF) 2 with an unidentified “KH + H 3 SiPh” reaction product (presumably containing KSiH 2 Ph and KSiH 3 ) gave the Ln II −SiH 3 complexes [(C 5 Me 5 )Ln(SiH 3 )(THF)(C 5 Me 5 )K(THF)] n (Ln = Sm ( 2a ), Eu ( 2b ), Yb ( 2c )) in 81−85% yields. Complexes 1a − c and 2b, c were structurally characterized by X-ray analyses. The “(C 5 Me 5 )K” unit in these complexes acted as a neutral stabilization ligand. An “intermolecular” interaction between the K atom and the Ln(II)-bound C 5 Me 5 group resulted in formation of a polymeric structure. In the case of 2b, c, an “interchain” interaction between the K atom and the SiH 3 group was also observed, which thus led to formation of a two-dimensional layer structure. Complexes 1a − c represent the first examples of structurally characterized (cyclopentadienyl)lanthanide(II) alkyl complexes and 2b, c the first examples of lanthanide(II)−SiH 3 complexes. The Sm II −CH(SiMe 3 ) 2 complex 1a showed high activity for the polymerization of ethylene and styrene through initiative one-electron transfer from the Sm(II) center to a monomer. The less reducing Eu(II) and Yb(II) analogues 1b, c showed no activity under the same conditions. In contrast, the SiH 3 complexes of Eu(II) ( 2b ) and Yb(II) ( 2c ) were active for the polymerization of ethylene and styrene, which was probably initiated by migratory addition of the SiH 3 group to a monomer. Complex 1a was also active for the block-copolymerization of ethylene with styrene.
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Hou et al. (2002) studied this question.