Unprecedented isospecific 3,4-polymerization of isoprene by cationic rare earth metal alkyl species resulting from a binuclear precursor

The isospecific 3,4-polymerization of isoprene has been achieved for the first time by use of a combination of a binuclear rare earth metal dialkyl complex, such as Me2Si(C5Me4)(mu-PCy)YCH2SiMe3]2 (Cy = cyclohexyl), and an equimolar amount of Ph3C]B(C6F5)4] as a catalyst system. A DFT calculation suggested that a binuclear monocationic monoalkyl species, such as Me2Si(C5Me4)(mu-PCy)Y(mu-CH2SiMe3)Y(mu-PCy)(C5Me4)SiMe2]+, in which the alkyl group bridges the two metal centers, could be the true catalyst species.