(Pentamethylcyclopentadienyl)lanthanide(II) Alkyl and Silyl Complexes: Synthesis, Structures, and Catalysis in Polymerization of Ethylene and Styrene

Abstract

The reactions of (C5Me5)2Ln(THF)2 with 1 equiv of KCH(SiMe3)2 in THF afforded the corresponding Ln(II) alkyl complexes [(C5Me5)Ln(CH(SiMe3)2)(C5Me5)K(THF)2]n (Ln = Sm (1a), Eu (1b), Yb (1c)) in 90−92% isolated yields. In the presence of PhSiH3 the reactions of (C5Me5)2Ln(THF)2 with an unidentified “KH + H3SiPh” reaction product (presumably containing KSiH2Ph and KSiH3) gave the LnII−SiH3 complexes [(C5Me5)Ln(SiH3)(THF)(C5Me5)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 “(C5Me5)K” unit in these complexes acted as a neutral stabilization ligand. An “intermolecular” interaction between the K atom and the Ln(II)-bound C5Me5 group resulted in formation of a polymeric structure. In the case of 2b,c, an “interchain” interaction between the K atom and the SiH3 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)−SiH3 complexes. The SmII−CH(SiMe3)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 SiH3 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 SiH3 group to a monomer. Complex 1a was also active for the block-copolymerization of ethylene with styrene.