This chapter surveys the publications except patents related to cis-1,4-, trans-1,4-, 3,4-regio-, and stereoselective polymerizations of 1,3-conjugated dienes with rare-earth metal-based catalytic systems during the past decade from 1999 to 2009. The concerned catalyst systems are classified into the conventional Ziegler- Natta catalysts, the modified Ziegler-Natta catalysts, and the single-site cationic systems composed of lanthanocene and noncyclopentadienyl precursors, respec- tively. For the conventional Ziegler-Natta catalysts of the most promising indus- try applicable recipe, the multicomponents based on lanthanide carboxylate or phosphate or alkoxide precursors, research works concern mainly about optimiz- ing the catalyst preparation and polymerization techniques. Special emphases are put on the factors that influence the catalyst homogeneority, catalytic activity and efficiency, as well as cis-1,4-selectivity. Meanwhile, tailor-made lanthanide ary- loxide and amide complexes are designed and fully characterized to mimic the conventional Ziegler-Natta catalysts, anticipated to elucidate the key processes, alkylation and cationization, for generating the active species. Regarding to the single-site catalytic systems generally comprising well-defined complexes contain- ing lanthanide-carbon bonds, investigations cover their versatile catalytic activity and efficiency, and the distinguished regio- and stereoselectivity for both poly- merization of dienes and copolymerization of dienes with alkenes. The correla- tion between the sterics and electronics of ligands and the molecular structures of the complexes and their catalytic performances are highlighted. The isolation of the probable active species in these polymerization processes from the stoichiomet- ric reactions of the precursors with activators will be presented.

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Polymerization of 1,3-Conjugated Dienes with Rare-Earth Metal Precursors

Highly Cis-1,4-Selective Living Polymerization of 1,3-Conjugated Dienes and Copolymerization with ε-Caprolactone by Bis(phosphino)carbazolide Rare-Earth-Metal Complexes

The development of new generations of polymerization catalysts and technology for efficient, selective synthesis of novel polymer materials having well-controlled microstructures and desired properties has been a long-standing research subject of both academic and industrial scientists. In this endeavor, exploring the potential of untapped elements is an important strategy. Recently, the chainshuttling copolymerization of two different monomers by two Group 4 metal catalysts that show different monomer selectivities has emerged as a powerful technology for the preparation of olefin block copolymers with different segments. In contrast, the potential of rare-earth catalysts in such chain-shuttling copolymerization has remained unexplored to date. 3] Moreover, the success of chain-shuttling copolymerization reported to date has been limited mostly to the copolymerization of ethylene and propylene (or 1-hexene), while the chain-shuttling copolymerization of styrene and a conjugated diene such as isoprene or butadiene has not been reported. We report herein the first example of chain-shuttling copolymerization of styrene, isoprene, and butadiene by two different scandium catalysts. In the presence of scandium catalyst 1 (Scheme 1), which shows high activity and high selectivity for the syndiotactic polymerization of styrene but low activity and low selectivity for isoprene, and scandium catalyst 2, which shows high activity and high cis-1,4selectivity for the polymerization of isoprene but low activity and low selectivity for styrene, together with a chainshuttling agent, the copolymerization of styrene and isoprene has been achieved regioand stereoselectively at each monomer, affording for the first time block copolymers with perfect syndiotactic polystyrene (sPS) and highly regulated cis-1,4-polyisoprene (PIP) blocks. In a similar manner, the terpolymerization of styrene, isoprene, and butadiene has also been achieved for the first time to give terpolymers containing perfect sPS, highly regulated cis-1,4-PIP and highly regulated cis-1,4-PBD blocks. By replacement of the catalyst 2 with a catalyst 3, which showed high 3,4-selectivity for the polymerization of isoprene in the chain-shuttling polymerization of styrene and isoprene, novel styrene–isoprene block copolymers with sPS and 3,4-PIP blocks have been obtained for the first time. Some representative results of the polymerization and copolymerization of styrene and isoprene by three different Sc catalysts 1, 2, and 3 (Scheme 1) under various conditions are summarized in Table 1. As reported, the half-sandwich scandium dialkyl complex 1 bearing the sterically demanding C5Me4SiMe3 ligand in combination with [Ph3C][B(C6F5)4] showed high activity and high syndiospecific selectivity (rrrr> 99%) for the polymerization of styrene (Table 1, run 1), but low activity and poor regioand stereoselectivity for the polymerization of isoprene (Table 1, run 4). The smaller C5H5-bound Sc analogue 2 exhibited much lower activity and no stereoselectivity for the polymerization of styrene (Table 1, run 2) but showed high activity and high cis-1,4selectivity (97 %) for the polymerization of isoprene (Table 1, run 5) under the same conditions. In the presence of both 1 and 2 without a chain-shuttling agent, the copolymerization of styrene and isoprene gave a polymer mixture of cis-1,4-PIP homopolymer and a styrene–isoprene copolymer containing mainly sPS blocks with mixed 1,4-/3,4-PIP units, as confirmed by solvent extraction (Table 1, run 7). In sharp contrast, when five equivalents (per Sc center) of iBu3Al (TIBA) were added to the above reaction system, the copolymerization of styrene and isoprene took place selectively and rapidly to give the block copolymer containing perfect sPS (rrrr> 99 %) and highly regulated cis-1,4-PIP (97 % selectivity) blocks with high molecular weight (Mn = 109.4 kg mol ) and narrow molecular-weight distribution (Mw/Mn = 1.43, Table 1, run 8). When the amount of TIBA was increased from five equivScheme 1. Scandium catalysts of different activities and selectivities. 1: High activity and high syndiospecific selectivity for styrene polymerization but low activity and low selectivity for isoprene polymerization. 2 : High activity and high cis-1,4-selectivty for isoprene or butadiene polymerization but low activity and low selectivity for styrene polymerization. 3 : High activity and high 3,4-selectivity for isoprene polymerization but low activity for styrene polymerization.

Chain‐Shuttling Polymerization at Two Different Scandium Sites: Regio‐ and Stereospecific “One‐Pot” Block Copolymerization of Styrene, Isoprene, and Butadiene

β-Diketiminato Rare-Earth Metal Complexes. Structures, Catalysis, and Active Species for Highly cis-1,4-Selective Polymerization of Isoprene

Living catalyzed-chain-growth polymerization and block copolymerization of isoprene by rare-earth metal allyl precursors bearing a constrained-geometry-conformation ligand

The first aryldiimine NCN-pincer ligated rare earth metal dichlorides (2,6-(2,6-C6H3R2NCH)2-C6H3)LnCl2(THF)2 (Ln = Y, R = Me (1), Et (2), iPr (3); R = Et, Ln = La (4), Nd (5), Gd (6), Sm (7), Eu (8), Tb (9), Dy (10), Ho (11), Yb (12), Lu (13)) were successfully synthesized via transmetalation between 2,6-(2,6-C6H3-R2NCH)2-C6H3Li and LnCl3(THF)1∼35 These complexes are isostructural monomers with two coordinating THF molecules, where the pincer ligand coordinates to the central metal ion in a κC:κN:κN‘ tridentate mode, adopting a meridional geometry Complexes 1−6, 9−11, and 13 combined with aluminum tris(alkyl)s and [Ph3C][B(C6F5)4] established a homogeneous Ziegler−Natta catalyst system, which exhibited high activities and excellent cis-1,4 selectivities for the polymerizations of butadiene (Tp = 25 °C, 999%; 0 °C, 100%) and isoprene (Tp = 25 °C, 988%) Remarkably, such high cis-1,4 selectivity almost remained at elevated polymerization temperatures up to 80 °C and did not vary with the type of the ce

Highly cis-1,4 Selective Polymerization of Dienes with Homogeneous Ziegler−Natta Catalysts Based on NCN-Pincer Rare Earth Metal Dichloride Precursors

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Highly cis-1,4 Selective Polymerization of Dienes with Homogeneous Ziegler−Natta Catalysts Based on NCN-Pincer Rare Earth Metal Dichloride Precursors