Dinuclear Rare-Earth Metal Alkyl Complexes Supported by Indolyl Ligands in μ-η2:η1:η1 Hapticities and their High Catalytic Activity for Isoprene 1,4-cis-Polymerization

Two series of new dinuclear rare-earth metal alkyl complexes supported by indolyl ligands in novel -(2):(1):(1) hapticities are synthesized and characterized. Treatment of [RE(CH2SiMe3)(3)(thf)(2)] with 1equivalent of 3-(tBuNCH)C8H5NH (L-1) in THF gives the dinuclear rare-earth metal alkyl complexes trans-[(-(2):(1):(1)-3-{tBuNCH(CH2SiMe3)}Ind)RE(thf)(CH2SiMe3)](2) (Ind=indolyl, RE=Y, Dy, or Yb) in good yields. In the process, the indole unit of L-1 is deprotonated by the metal alkyl species and the imino CN group is transferred to the amido group by alkyl CH2SiMe3 insertion, affording a new dianionic ligand that bridges two metal alkyl units in -(2):(1):(1) bonding modes, forming the dinuclear rare-earth metal alkyl complexes. When L-1 is reduced to 3-(tBuNHCH(2))C8H5NH (L-2), the reaction of [Yb(CH2SiMe3)(3)(thf)(2)] with 1equivalent of L-2 in THF, interestingly, generated the trans-[(-(2):(1):(1)-3-{tBuNCH(2)}Ind)Yb(thf)(CH2SiMe3)](2) (major) and cis-[(-(2):(1):(1)-3-{tBuNCH(2)}Ind)Yb(thf)(CH2SiMe3)](2) (minor) complexes. The catalytic activities of these dinuclear rare-earth metal alkyl complexes for isoprene polymerization were investigated; the yttrium and dysprosium complexes exhibited high catalytic activities and high regio- and stereoselectivities for isoprene 1,4-cis-polymerization.