DEVELOPMENT OF MIXED-LIGAND-SUPPORTED LANTHANIDE POLYMERIZATION CATALYSTS

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(1) Reactions of (C_5Me_5)_2Sm(THF)_2 with 1 equiv of K(ER) in THF gave in high yields the C_5Me_5/ER-ligated Sm(II) complexes [(C_5Me_5)Sm(THF)_m(ER)(μ-C_5Me_5)K(THF)_n]_∞ (m=0 or 1 ; n=1 or 2 ; ER=OC_6H_2^tBu_2-2,6-Me-4 (1a), OC_6H_3^iPr_2-2,6 (1b), SC_6H_2^iPr_3-2,4,6 (1c), NHC_6H_2^tBu_3-2,4,6 (1d), or N(SiMe_3)_2 (1e)), in which the "(C_5Me_5)K(THF)_n" unit acts as a neutral coordination ligand bonding to the Sm(II) center with the "C_5Me_5" part. These complexes, particularly 1a-c, showed unique reactivity toward styrene and ethylene, which can not only polymerize styrene and ethylene, but also copolymerize them into block styrene-ethylene copolymers under the presence of both monomers. Among the ER ligands, the thiolate ligand SC_6H_2^iPr_3-2,4,6 (1c) showed the highest selectivity for the block copolymerization of styrene and ethylene, while the aryloxide OC_6H_2^tBu_2-2,6-Me-4 (1a) and the silylamide N(SiMe_3)_2 (1e) gave the highest activity for the polymerization of ethylene and that of styrene, respectively.(2) Addition of an appropriate cocatalyst such as MMAO or AlR_3/[Ph_3C][B(C_6F_5)_4] to the samarocene complex (C_5Me_5)_2Sm(THF)_2 or (C_5Me_5)_2Sm(μ-Me)_2AlMe_2 afforded a novel catalytic system for stereospecific 1,4-cis living polymerization of butadiene and copolymerization of butadiene with styrene.(3) The samarium(II) bis (aryloxide) complex Sm(OAr)_2(THF)_3 (Ar=OC_6H_2^tBu_2-2,6-Me-4) showed an extremely high activity for ring-opening polymerization of ε-caprolactone and δ-valerolactone and copolymerization of ε-caprolactone with γ-butyrolactone.