Stereospecific Polymerization of 1,3-Butadiene with Samarocene-Based Catalysts

Cationic Alkyl Complexes of the Rare‐Earth Metals: Synthesis, Structure, and Reactivity

“…[86] Further evidence that cationic hydrocarbyl complexes act as the active species is given by the following observation: The activation of the cationic bis(pentamethylcyclopentadienyl) complexes [LnCp* 2 ][B(C 6 F 5 ) 4 ] (Ln ¼ Pr, Nd, Sm) with Al(i-Bu) 3 was reported to afford highly cis-1,4 selective initiators for 1,3-butadiene polymerization (Table 7). [12,83,87] The above findings may also imply that, in the case of the industrially applied multicomponent catalysts typically consisting of lanthanide carboxylate, aluminum alkyl and Lewis acid, discrete cationic alkyl species may be formed in situ or exist in equilibrium with non-ionic compounds (Scheme 14). [88,89] …”

Polymer Structure Control Based on Crystal Engineering for Materials Design

“…[87][88][89][90] Table IV summarizes the typical examples of stereospecific polymerization of 1,3-butadiene to give highly controlled stereoregular polymers. [91][92][93][94][95][96][97][98][99][100] The stereochemical structure of polymers produced from 1,4-disubstituted butadienes is represented not only by cis-trans isomerism but also by isotactic-syndiotactic and erythro-threo (or mesoracemo) relationships. 48 Stereoregular polymers from 1,4-disubstituted butadienes are referred to as tritactic polymers due to the presence of three elements of stereoisomerism for each monomer unit, two pseudoasymmetric carbon centers and a double bond.…”

Cationic Alkyl Rare‐Earth Metal Complexes Bearing an Ancillary Bis(phosphinophenyl)amido Ligand: A Catalytic System for Living cis‐1,4‐Polymerization and Copolymerization of Isoprene and Butadiene

“…However, similar to the heterogeneous industrial catalysts, such binary or ternary catalyst systems generally lack "livingness" and yield polymers with rather broad molecular-weight distributions. On the other hand, lanthanide metallocene-based catalyst sys- [4b] have been found to afford polymers with both high cis-1,4 selectivity (up to 99 %) and a narrow molecularweight distribution, or "livingness" (M w /M n = 1.20-1.23), in the polymerization of butadiene under appropriate conditions, [4] however, the polymerization of isoprene has not been achieved in a "living" fashion with such catalyst systems.[4f]Very recently, the combination of a Nd/Mg heterotrimetallic allyl complex with methylaluminoxane (MAO) was reported to show both high cis-1,4 selectivity (95-99 %) and a relatively narrow molecular-weight distribution (M w /M n = 1.3-1.7) for the polymerization of isoprene. [5,6] A common feature in the reported catalyst systems is that they all require an aluminum additive, such as AlR 2 Cl, AlR 3 , or MAO, to show high activity and high cis-1,4 selectivity, which makes it difficult to identify the true catalytic species and to understand the mechanistic aspects of the polymerization process.…”

“…[5,6] A common feature in the reported catalyst systems is that they all require an aluminum additive, such as AlR 2 Cl, AlR 3 , or MAO, to show high activity and high cis-1,4 selectivity, which makes it difficult to identify the true catalytic species and to understand the mechanistic aspects of the polymerization process. [2][3][4][5][6][7][8] Recently, cationic methylyttrium species, such as [YMe 2Àn (solv) x ] n+1 (n = 0, 1; solv = solvent), have been reported to show activity for the polymerization of butadiene and isoprene in the absence of an aluminum additive, but the use of a bulky alkyl aluminum additive, such as Al(iBu) 3 , was again essential to achieve significant cis-1,4 selectivity (67 % vs. 90 % for isoprene polymerization with and without Al(iBu) 3 , respectively).[9] A related aluminum-free cationic alkyl yttrium species bearing silylene-linked cyclopentadienylphosphido ligands shows exclusive 3,4-selectivity for the polymerization of isoprene, while a cationic alkyl yttrium species bearing the C 5 Me 4 SiMe 3 ligand yields a mixture of 3,4-and 1,4-polyisoprenes under similar conditions.[10] The search for more selective, simpler, and better-controlled catalyst systems for the cis-1,4 polymerization and copolymerization of isoprene and butadiene is therefore of interest and importance.Herein we report a new catalyst system based on a cationic alkyl rare-earth metal species bearing an ancillary bis(phosphinophenyl)amido (PNP) ligand. This catalyst system provides extremely high cis-1,4 selectivity (99 %) and excellent livingness (M w /M n = 1.05-1.13) with no need for an aluminum additive to show high activity and high selectivity for the polymerization of isoprene and butadiene, and can also be applied to the copolymerization of isoprene and butadiene in a living cis-1,4 fashion.…”

“…However, similar to the heterogeneous industrial catalysts, such binary or ternary catalyst systems generally lack "livingness" and yield polymers with rather broad molecular-weight distributions. On the other hand, lanthanide metallocene-based catalyst sys- 4 ], [4b] have been found to afford polymers with both high cis-1,4 selectivity (up to 99 %) and a narrow molecularweight distribution, or "livingness" (M w /M n = 1.20-1.23), in the polymerization of butadiene under appropriate conditions, [4] however, the polymerization of isoprene has not been achieved in a "living" fashion with such catalyst systems.…”