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 [Ph
3C] [B(C
6F
5)
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 AlMe
3. 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.
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