Copolymerization of ethylene with norbornene catalyzed by cationic rare earth metal fluorenyl functionalized N-heterocyclic carbene complexes.

Rare earth metal bis(alkyl) complexes attached by fluorenyl modified N-heterocyclic carbene (NHC) (Flu-NHC)Ln(CH(2)SiMe(3))(2) (Flu-NHC = (C(13)H(8)CH(2)CH(2)(NCHCCHN)C(6)H(2)Me(3)-2,4,6); Ln = Sc (2a); Y (2b); Ho (2c); Lu (2d)), ((tBu)Flu-NHC)Ln(CH(2)SiMe(3))(2) ((tBu)Flu-NHC = 2,7-(t)Bu(2)C(13)H(6)CH(2)CH(2)(NCHCCHN)C(6)H(2)Me(3)-2,4,6; Ln = Sc (1a); Lu (1d)) and attached by indenyl modified N-heterocyclic carbene (Ind-NHC)Ln(CH(2)SiMe(3))(2) (Ind-NHC = C(9)H(6)CH(2)CH(2)(NCHCCHN)C(6)H(2)Me(3)-2,4,6; Ln = Sc (3a); Lu (3d)), under the activation of Al(i)Bu(3) and [Ph(3)C][B(C(6)F(5))(4)], showed varied catalytic activities toward homo- and copolymerization of ethylene and norbornene. Among which the scandium complexes, in spite of ligand type, exhibited medium to high catalytic activity for ethylene polymerization (10(5) g mol(Sc)(-1) h(-1) atm(-1)), but all were almost inert to norbornene polymerization. Remarkably, higher activity was found for the copolymerization of ethylene and norbornene when using Sc based catalytic systems, which reached up to 5 x 10(6) g mol(Sc)(-1) h(-1) atm(-1) with 2a. The composition of the isolated copolymer was varying from random to alternating according to the feed ratio of the two monomers (r(E) = 4.1, r(NB) = 0.013). The molecular structure of complex 1d was characterized by X-ray analysis. The influences of structural factors of complexes and polymerization conditions on both the catalytic activity and the norbornene content in the copolymer were discussed.