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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
40
Citations
72
References
2016
Year
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(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>3</sub>(thf)<sub>2</sub>] with 1 equiv. of 3-(CyN[double bond, length as m-dash]CH)C<sub>8</sub>H<sub>5</sub>NH in toluene or in THF afforded dinuclear rare-earth metal alkyl complexes having indolyl ligands in different hapticities with central metals {[η<sup>2</sup>:η<sup>1</sup>-μ-η<sup>1</sup>-3-(CyNCH(CH<sub>2</sub>SiMe<sub>3</sub>))Ind]RE-(thf)(CH<sub>2</sub>SiMe<sub>3</sub>)}<sub>2</sub> (Cy = cyclohexyl, Ind = Indolyl, RE = Yb (1), Er (2), Y (3)) or {[η<sup>1</sup>-μ-η<sup>1</sup>-3-(CyNCH(CH<sub>2</sub>SiMe<sub>3</sub>))Ind]RE-(thf)<sub>2</sub>(CH<sub>2</sub>SiMe<sub>3</sub>)}<sub>2</sub> (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(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>3</sub>(thf)<sub>2</sub>] with 1 equiv. of 3-t-butylaminomethylindole 3-(<sup>t</sup>BuNHCH<sub>2</sub>)C<sub>8</sub>H<sub>5</sub>NH in THF afforded the unexpected trinuclear erbium alkyl complex [η<sup>2</sup>:η<sup>1</sup>-μ-η<sup>1</sup>-3-(<sup>t</sup>BuNCH<sub>2</sub>)Ind]<sub>4</sub>Er<sub>3</sub>(thf)<sub>5</sub>(CH<sub>2</sub>SiMe<sub>3</sub>) (8), which can also be prepared by reaction of 3 equiv. of [Er(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>3</sub>(thf)<sub>2</sub>] with 4 equiv. of 3-(<sup>t</sup>BuNHCH<sub>2</sub>)C<sub>8</sub>H<sub>5</sub>NH in THF. Accordingly, complexes [η<sup>2</sup>:η<sup>1</sup>-μ-η<sup>1</sup>-3-(<sup>t</sup>BuNCH<sub>2</sub>)Ind]<sub>4</sub>RE<sub>3</sub>(thf)<sub>5</sub>(CH<sub>2</sub>SiMe<sub>3</sub>) (RE = Y (9), Dy (10)) were prepared by reactions of 3 equiv. of [RE(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>3</sub>(thf)<sub>2</sub>] with 4 equiv. of 3-(<sup>t</sup>BuNHCH<sub>2</sub>)C<sub>8</sub>H<sub>5</sub>NH in THF. Reactions of [RE(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>3</sub>(thf)<sub>2</sub>] with 1 equiv. of 3-t-butylaminomethylindole 3-(<sup>t</sup>BuNHCH<sub>2</sub>)C<sub>8</sub>H<sub>5</sub>NH in THF, followed by treatment with 1 equiv. of [(2,6-<sup>i</sup>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>)N[double bond, length as m-dash]CHNH(C<sub>6</sub>H<sub>3</sub><sup>i</sup>Pr<sub>2</sub>-2,6)] afforded, after workup, the dinuclear rare-earth metal complexes [η<sup>1</sup>-μ-η<sup>1</sup>:η<sup>1</sup>-3-(<sup>t</sup>BuNCH<sub>2</sub>)Ind][η<sup>1</sup>-μ-η<sup>1</sup>:η<sup>3</sup>-3-(<sup>t</sup>BuNCH<sub>2</sub>)Ind]RE<sub>2</sub>(thf)[(η<sup>3</sup>-2,6-<sup>i</sup>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>)NCHN(C<sub>6</sub>H<sub>3</sub><sup>i</sup>Pr<sub>2</sub>-2,6)]<sub>2</sub>(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.
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