Di and trinuclear rare-earth metal complexes supported by 3-amido appended indolyl ligands: synthesis, characterization and catalytic activity towards isoprene 1,4-cis polymerization.

Different di and trinuclear rare-earth metal complexes supported by 3-amido appended indolyl ligands were synthesized and their catalytic activities towards isoprene polymerization were investigated. Treatment of [RE(CH2 SiMe3 )3 (thf)2 ] with 1 equiv. of 3-(CyN[double bond, length as m-dash]CH)C8 H5 NH in toluene or in THF afforded dinuclear rare-earth metal alkyl complexes having indolyl ligands in different hapticities with central metals {[η2 :η1 -μ-η1 -3-(CyNCH(CH2 SiMe3 ))Ind]RE-(thf)(CH2 SiMe3 )}2 (Cy = cyclohexyl, Ind = Indolyl, RE = Yb (1), Er (2), Y (3)) or {[η1 -μ-η1 -3-(CyNCH(CH2 SiMe3 ))Ind]RE-(thf)2 (CH2 SiMe3 )}2 (RE = Yb (4), Er (5), Y (6), Gd (7)), respectively. These two series of dinuclear complexes could be transferred to each other easily by only changing the solvents in the process. Reaction of [Er(CH2 SiMe3 )3 (thf)2 ] with 1 equiv. of 3-t-butylaminomethylindole 3-(t BuNHCH2 )C8 H5 NH in THF afforded the unexpected trinuclear erbium alkyl complex [η2 :η1 -μ-η1 -3-(t BuNCH2 )Ind]4 Er3 (thf)5 (CH2 SiMe3 ) (8), which can also be prepared by reaction of 3 equiv. of [Er(CH2 SiMe3 )3 (thf)2 ] with 4 equiv. of 3-(t BuNHCH2 )C8 H5 NH in THF. Accordingly, complexes [η2 :η1 -μ-η1 -3-(t BuNCH2 )Ind]4 RE3 (thf)5 (CH2 SiMe3 ) (RE = Y (9), Dy (10)) were prepared by reactions of 3 equiv. of [RE(CH2 SiMe3 )3 (thf)2 ] with 4 equiv. of 3-(t BuNHCH2 )C8 H5 NH in THF. Reactions of [RE(CH2 SiMe3 )3 (thf)2 ] with 1 equiv. of 3-t-butylaminomethylindole 3-(t BuNHCH2 )C8 H5 NH in THF, followed by treatment with 1 equiv. of [(2,6-i Pr2 C6 H3 )N[double bond, length as m-dash]CHNH(C6 H3 i Pr2 -2,6)] afforded, after workup, the dinuclear rare-earth metal complexes [η1 -μ-η1 :η1 -3-(t BuNCH2 )Ind][η1 -μ-η1 :η3 -3-(t BuNCH2 )Ind]RE2 (thf)[(η3 -2,6-i Pr2 C6 H3 )NCHN(C6 H3 i Pr2 -2,6)]2 (RE = Er (11), Y (12)) having the indolyl ligands bonded with the rare-earth metal in different ligations. All new complexes 1-12 were fully characterized by spectroscopic methods and elemental analyses, and their structures were determined by X-ray crystallographic analyses. It was found that, except for complexes 1, 4, 11 and 12, all complexes were highly efficient catalysts for selective isoprene polymerization (up to 99% 1,4-cis selectivity) with the cooperation of co-catalysts, and the trinuclear complexes displayed advantages over dinuclear complexes in terms of molecular weight of polymers.