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(CH2SiMe3)3(thf)2] with 1 equiv. of 3-(CyN[double bond, length as m-dash]CH)C8H5NH 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(CH2SiMe3))Ind]RE-(thf)(CH2SiMe3)}2 (Cy = cyclohexyl, Ind = Indolyl, RE = Yb (1), Er (2), Y (3)) or {[η1-µ-η1-3-(CyNCH(CH2SiMe3))Ind]RE-(thf)2(CH2SiMe3)}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(CH2SiMe3)3(thf)2] with 1 equiv. of 3-t-butylaminomethylindole 3-(tBuNHCH2)C8H5NH in THF afforded the unexpected trinuclear erbium alkyl complex [η2:η1-µ-η1-3-(tBuNCH2)Ind]4Er3(thf)5(CH2SiMe3) (8), which can also be prepared by reaction of 3 equiv. of [Er(CH2SiMe3)3(thf)2] with 4 equiv. of 3-(tBuNHCH2)C8H5NH in THF. Accordingly, complexes [η2:η1-µ-η1-3-(tBuNCH2)Ind]4RE3(thf)5(CH2SiMe3) (RE = Y (9), Dy (10)) were prepared by reactions of 3 equiv. of [RE(CH2SiMe3)3(thf)2] with 4 equiv. of 3-(tBuNHCH2)C8H5NH in THF. Reactions of [RE(CH2SiMe3)3(thf)2] with 1 equiv. of 3-t-butylaminomethylindole 3-(tBuNHCH2)C8H5NH in THF, followed by treatment with 1 equiv. of [(2,6-iPr2C6H3)N[double bond, length as m-dash]CHNH(C6H3iPr2-2,6)] afforded, after workup, the dinuclear rare-earth metal complexes [η1-µ-η1:η1-3-(tBuNCH2)Ind][η1-µ-η1:η3-3-(tBuNCH2)Ind]RE2(thf)[(η3-2,6-iPr2C6H3)NCHN(C6H3iPr2-2,6)]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.

Rare-earth alkyl complexes supported by formamidinate ligands: synthesis, structure, and catalytic activity for isoprene polymerization.

A series of rare-earth metal monoalkyl complexes supported by N,N'-di(2,6-dialkylphenyl)formamidinate ligand (L)2RECH2SiMe3·thf [L(1) = HC(N-2,6-Me2C6H3)2, RE = Y (1), L(2) = HC(N-2,6-(i)Pr2C6H3)2, RE = Y (2), Er (3), Dy (4), Sm (5), and Nd (6)] were synthesized by alkyl elimination reaction or by salt metathesis reaction in good yields. All complexes were characterized by elemental analyses, FT-IR spectroscopy and single crystal X-ray diffraction. In combination with [Ph3C][B(C6F5)4] and alkylaluminium, these complexes displayed a good activity towards isoprene polymerization to give polyisoprenes with high molecular weight (M(n) > 10(4)) and narrow molecular distribution (PDI < 2.0). The influence of alkylaluminium, central metal, temperature, sequence of addition of alkylaluminium and [Ph3C][B(C6F5)4] on the polymerization of isoprene was studied. It was interesting to find that addition of the cocatalysts sequence has a great influence on the regioselectivity of the polymerization. High 1,4-regioselectivity polymerizations of isoprene (as high as 98%) were observed when the catalysts were added in the order [RE]/[alkylaluminum]/[borate].

Synthesis, structure, and reactivity of lanthanide complexes incorporating indolyl ligands in novel hapticities.

The chemistry of interactions of 2-(2,6-diisopropylphenylaminomethylene)indole ligand (1) with europium and ytterbium amides is described. Reaction of 2-(2,6-diisopropylphenylaminomethylene)indole 2-(2,6-i-Pr2C6H3NHCH2)C8H5NH (1) with europium amide [(Me3Si)2N]3Eu(III)(µ-Cl)Li(THF)3 afforded a novel europium(II) complex formulated as {[µ-η(6):η(1):η(1)-2-(2,6-i-Pr2C6H3N═CH)C8H5N]Eu[2-(2,6-i-Pr2C6H3N═CH)C8H5N]}2 (2), having a bridged indolyl ligand in the novel µ-η(6):η(1):η(1) hapticities with the reduction of europium(III) to europium(II) and the oxidation of amino to imino group. Reaction of 2-(2,6-diisopropylphenylaminomethylene)indole 2-(2,6-i-Pr2C6H3NHCH2)C8H5NH (1) with ytterbium(III) amide [(Me3Si)2N]3Yb(III)(µ-Cl)Li(THF)3 produced the only deprotonated ytterbium(III) complex formulated as [2-(2,6-i-Pr2C6H3NCH2)C8H5N]Yb[N(SiMe3)2](THF)2 (3), having an η(1) hapticity indolyl ligand. Reaction of 2 with formamidine [(2,6-Me2C6H3)NCHNH(C6H3Me2-2,6)] produced {[µ-η(3):η(1):η(1)-2-(2,6-i-Pr2C6H3N═CH)C8H5N]Eu[(2,6-Me2C6H3)NCHN(C6H3Me2-2,6)](THF)}2 (4), which has a bridged indolyl ligand in the novel µ-η(3):η(1):η(1) hapticities, whereas the reaction of 2 with the more sterically bulky formamidine [(2,6-i-Pr2C6H3)NCHNH(C6H3i-Pr2-2,6)] afforded complex {[µ-η(2):η(1):η(1)-2-(2,6-i-Pr2C6H3N═CH)C8H5N]Eu[(2,6-i-Pr2C6H3)N═CHN(C6H3i-Pr2-2,6)](THF)}2 (5), having the indolyl ligand in the novel µ-η(2):η(1):η(1) hapticities. The results represent the first example of organometallic complexes having indolyl ligands in the novel µ-η(6):η(1):η(1), µ-η(3):η(1):η(1), and µ-η(2):η(1):η(1) bonding modes with metal.