Living 3,4-(Co)Polymerization of Isoprene/Myrcene and One-Pot Synthesis of a Polyisoprene Blend Catalyzed by Binuclear Rare-Earth Metal Amidinate Complexes

Mononuclear amidinate yttrium complex C4H9C(NR)(2)Y(o-CH2C6H4NMe2)(2) (R=2,6-iPr(2)C(6)H(3)) and a series of binuclear rare-earth metal complexes bearing a bridged amidinate ligand [(RN)(2)C(CH2)(4)C(NR)(2)][RE{CH2C6H4(o-NMe2)}(2)](2) (R=2,6-iPr(2)C(6)H(3), RE=Y, Lu, Sc) were synthesized and fully characterized. The catalytic behavior of these complexes for (co)polymerization of conjugated dienes such as isoprene and myrcene in the presence of co-catalyst [Ph3C][B(C6F5)(4)] was investigated. These catalytic systems show impressively high activity and 3,4-regioselectivity in living (co)polymerization. The binuclear bridged amidinate yttrium catalytic system not only exhibits the highest activity among the reported catalytic systems for 3,4-polymerization of isoprene but also allows the steady polymerization in a living manner from 20 to 80 degrees C. Compared with the dramatic drop of 3,4-selectivity for the mononuclear analogue, the binuclear catalytic system still shows moderate 3,4-selectivity at 80 degrees C. Moreover, a facile one-pot synthetic strategy for a polymer blend containing 3,4- and 1,4-polyisoprene (PIP) was established through the in situ modification of the active amidinate yttrium species by addition of an excess amount of AlMe3.