Ethylene polymerization lanthanide complexes

As described in Section 9.1.2.2.3, several lanthanocene alkyls are known to be ethylene polymerization catalysts.221,226-229 Both (188) and (190) have been reported to catalyze the block copolymerization of ethylene with MMA (as well as with other polar monomers including MA, EA and lactones).229 The reaction is only successful if the olefin is polymerized first reversing the order of monomer addition, i.e., polymerizing MMA first, then adding ethylene only affords PMMA homopolymer. In order to keep the PE block soluble the Mn of the prepolymer is restricted to <12,000. Several other lanthanide complexes have also been reported to catalyze the preparation of PE-b-PMMA,474 76 as well as the copolymer of MMA with higher olefins such as 1-hexene.477... 

Table 12.7 Ethylene polymerization based on supported group 3 and lanthanide metallocene complexes-examples from relevant patents.

The second approach is a popular route to cationic lanthanide alkyl complexes, which have proven to be the important intermediates for ethylene polymerization and the stereospecific polymerization of diene [5]. Various monocationic lanthanide monoalkyl complexes have been synthesized by the alkyl abstraction/elimination reaction of lanthanide dialkyl complexes. The reaction of a bisbenzyl scandium complex supported by P-diketiminate with B(C6Fs)3 affords the cationic complex with a contact ion pair structure, in which a weak bonding between the cation and the anion exists (Figure 8.21) [77]. The reaction of an amidinate... 

In recent years, a large number of mono- and dicationic lanthanide alkyl complexes have been found to be efficient catalysts for ethylene polymerization, and in some cases, the dicationic lanthanide derivatives show higher activity and selectivity than their monocationic counterparts. Ionic radii of lanthanide metals also affect the catalytic behavior, and polymerization activity often increases with ionic radius [5, 76],... 

Various sterically unsaturated lanthanide complexes are active olefin polymerization precatalysts and it is far beyond the scope of this section to name every precatalyst. Rather, the exceptional features of a group of structurally characterized precatalysts which were originally designed for ethylene and propylene polymerization are emphasized (Structures 4-19 e. g., 4(Nd H)/THF means Cp2 NdH(THF) [29, 35]. Monomers such as CO, CO2, and RC=N usually deactivate this type of precatalyst by formation of strong Ln-O(N) linkages. 

Most of the lanthanide complexes that readily polymerize ethylene are inactive in propylene polymerization [48]. Thus, the complexes [ (Me3Si)2NC (NPr )2 2Ln(/i-H)]2 (Scheme 25) were also tested in catalysis of propylene and styrene polymerization. The yttrium derivative had low activity in propylene polymerization. Over a period of 2 h the monomer absorption reached 58 mol per mole of catalyst, whereupon the catalytic activity was lost. Complexes with Ln = La, Sm, Dd, and Yb were even less active and became inactive after 15-20 min. In styrene polymerization, only derivatives of smallest lanthanide metals showed catalytic activity. The Lu complex initiated polymerization of styrene (20°C, neat styrene, 5% of Lu complex), and 90% conversion was reached in 6 days. The polystyrene obtained had a high molecular weight Mn = 811,000gmor = 1250,000gmoF ), a narrow molecular-weight... 

Ethylene polymerization catalyzed by the well-characterized homogeneous lanthanide complexes [M(C5H R)2 ] 2 been studied. 

Described in this paper is a model system - one in which well-characterized lanthanide complexes exhibit high catalyst activities for ethylene polymerization but where the corresponding oligomerization of propene is sufficiently slowed so that stepwise insertion of the olefin can be studied quantitatively and all important intermediates observed or isolated. Emphasized in this paper is the effect of added Lewis acids and bases on the rate of olefin insertions, and comparison between ethylene and propene reactions. The catalysts, of general structure M(ri -Cp )2CH3 L (M = Yb, Lu ... 

Paolucci G, Bortoluzzi M, Napoli M, Longo P, Bertolasi V. The role of the ionic radius in the ethylene polymerization catalyzed by new group 3 and lanthanide scorpionate complexes. Mol Catal A. 2010 317 54-60. 

After rinzinger s initiator discussed above, a variety of metallocene- and non-met-allocene-based classes of ethylene polymerization initiators also including lanthanide metallocene complexes have been developed In the metallocene series, particularly noteworthy are ordan s MAO-free 1 -electron catalyst p r 1 h and Waymouth s bis 3 phenyl indenyl zirconium dichloride, the latter providing isotactic-atactic block polypropylene... 

Organolanthanide compounds are a new class of catalysts which are capable of polymerizing olefins. In 1990, Yasuda et al. discovered that Cp organolanthanide compounds are excellent catalysts for the living polymerization of ethylene. A variety of isolated and nonisolated lanthanide complexes have been used in the polymerization of ethylene. Typical examples are shown in Table 2 [40]. Surprisingly, organolanthanide... 

Actinide, lanthanide, and yttrium-based catalyst systems showing characteristics of reversible chain transfer in ethylene polymerization are summarized in Table 3. Samsel and Eisenberg claimed to observe the characteristics in ethylene polymerization with several metallocenes of actinides, such as the bis(pentamethylcyclopentadienyl) thorium complex 5 in combination with aluminum alkyl reagents. These systems catalyze the production of aluminum alkyl chain growth products at lower temperatures than those required by the uncatalyzed Ziegler process. The systems were limited to production of low-molecular-weight PE oligomers. 

Marks et al. reported the co-polymerization of ethylene and 1-hexene by using ansa-type complexes of lanthanide metals [127]. Recently, bulky alkyl substituted ansa-type metallocene complexes of yttrium have been reported to exhibit high activity for the polymerization of 1-hexane. [114, 119, 128]... 

At the first step, the insertion of MMA to the lanthanide-alkyl bond gave the enolate complex. The Michael addition of MMA to the enolate complex via the 8-membered transition state results in stereoselective C-C bond formation, giving a new chelating enolate complex with two MMA units one of them is enolate and the other is coordinated to Sm via its carbonyl group. The successive insertion of MMA afforded a syndiotactic polymer. The activity of the polymerization increased with an increase in the ionic radius of the metal (Sm > Y > Yb > Lu). Furthermore, these complexes become precursors for the block co-polymerization of ethylene with polar monomers such as MMA and lactones [215, 217]. 

The mechanism for polymerization of propylene with heterogeneous catalysts is very similar to that of ethylene. Studies with a homogeneous catalyst of a lanthanide element provided early mechanistic evidence. The complex used in these studies was 6.15. In 6.15 lutetium is in a 3+ oxidation state and has the electronic configuration of 4fu. In other words Lu3+ has a full/shell and 6.15 is a diamagnetic complex. 

The lithium amidinates are used as precursors for homoleptic lanthanide amidinates. Lanthanide amidinate complexes have a high catalytic activity in the polymerization of ethylene. They are also used in the manufacture of membranes. Lanthanide amidinate complexes 37 (La=Er, Y, Gd) are also obtained from alkyl metal complexes 36 and... 

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