|Synthesis of Novel Elastomers by Well-Defined Rare Earth Metal Catalysts
Organometallic Chemistry Laboratory, RIKENiThe Institute of Physical and Chemical Researchj. Wako, Saitama, Japan
Nippon Gomu Kyokaishi,(2008),81(10),414-418 General Review in Japanese
The cationic rare earth metal alkyl species bearing a bis(phosphine)amide ancillary ligand, generated by treatment of the corresponding dialkyl complexes with one equivalent of a borate compound can serve as an excellent catalyst for the living cis-1,4 polymerization of both isoprene and butadiene as well as for the living cis-1,4 copolymerization of isoprene and butadiene. On the other hand, the polymerization of isoprene by the binuclear monocationic monoalkyl species with cyclopentadienyl-phosphide ligands has afforded exclusively isotactic 3,4-polyisoprene with extremely high regio- and stereoselectivity (3,4-selectivity: 100 %, mmmm > 99 %). An amidinate-ligated aminobenzylyttrium complex, in combination with [Ph3C][B(C6F5)4], is an excellent catalyst system for the isospecific 3,4-polymerization of isoprene, while the regio- and stereoselectivity of this polymerization system can be dramatically switched from 3,4-isospecific to 1,4-cis selective by the addition of AlMe3. Cationic rare-earth hydride clusters, which are made by treating the corresponding neutral complexes with a borate activator, show high regio- and stereoselectivity for the polymerization of 1,3-cyclohexadiene (CHD) to afford soluble crystalline cis-1,4-linked poly(CHD) unavailable previously. The syndiospecific living copolymerization of styrene with isoprene has been achieved by use of a cationic half-sandwich scandium alkyl catalyst.
Rare Earth Metal, Yttrium, Cationic Monoalkyl Species, Cationic Polyhydride Cluster