Rare-Earth Metal Alkyl Complexes with 3-Arylamido-Functionalized Indolyl Ligands:Synthesis,Characterization and Reactivity

A series of dinuclear rare-earth metal alkyl complexes{[μ-η^2:η^1:η^1-3-(LNCH)(CH2SiMe3)Ind]RE-(CH2SiMe3)(THF)}2(L^1=2-tBuC6H4,RE=Y,Gd,Dy,Er,Yb;L^2=2,4,6-Me3C6H2,RE=Dy,Er;Ind=indolyl)and{[μ-η^2:η^1:η^1-3-(LNCH2)Ind]RE(CH2SiMe3)(THF)}2(L^1,RE=Y,Dy,Er,Yb;L^2,RE=Er,Yb)bearing 3-arylamido functionalized indolyl ligands having diverse bonding modes with metal ions were synthesized either by the insertion reaction of the imino group to the RE-C bond or by the alkane elimination reaction.In the preparation of above complexes,rare-earth metal alkyl complexes{[μ-η^5:η^1:η^1-3-(L^2 NCH)(CH2SiMe3)Ind]Gd(CH2SiMe3)(THF)}2 with aμ-η^5:η^1:η^1 coordination mode to the gadolinium ion and{[μ-η^3:η^1:η^1-3-(L^2NCH2)Ind]Dy(CH2SiMe3)(THF)}2 with aμ-η^3:η^1:η^1 coordination mode to the dysprosium ion were unexpectedly isolated.The reactions of 3-(L^2N=CH)lnd with Er(CH2SiMe3)3(THF)2 at room temperature,generated a tetranuclear imino-indolyl erbium intermediate{[μ-η^1:η^1-3-(L^2N=CH)Ind]Er(CH2SiMe3)2(THF)}4,which can transform into the amido functionalized indolyl erbium complex in hot toluene.Moreover,the reactivities of the newly synthesized ytterbium complex with N-heterocyclic compounds were investigated,affording the corresponding products of the mixed pyridyl-indolyl,imidazolyl-indolyl,and ortho-metalated complexes.The yttrium complexes showed a high regioselectivity and steroselectivity for the isoprene polymerization with 1,4-trans selectivity up to 91.7%and 1,4-cis selectivity up to 96.1%in the presence of cocatalysts,respectively.