Olefin polymerization, lanthanide

C-H Bond activation, with lanthanides Ethylene polymerization, with lanthanides Zeigler-Natta catalyst, lanthanide Diene polymerization, with lanthanides Olefin polymerization, with lanthanides Butadiene polymerization, with lanthanides Isoprene polymerization, with lanthanides Anionic propagation, at lanthanides Living polymers, at lanthanides Pseudo-living polymers, at lanthanides Reaction orders, diene polymerization Active sites, diene polymerization... 

Chemists became first interested in catalytic applications of organolanthanides when it turned out, that some lanthanide organometallics are highly active as olefin polymerization catalysts [8], The first indications of catalytic activity of organolanthanides came from the observation, that active species were formed... 

Early mechanistic studies concerning organolanthanide-catalyzed olefin polymerization reactions showed that insertion of the unsaturated hydrocarbon into the lanthanide-carbon cr-bond is a key step. It was first demonstrated for the... 

Patents have been reported for a series of bimetallic metallocene catalysts based on lanthanide and group IV metals. The bridging ligand is a substituted ethyl-linked fluorenyl indenyl bearing a substituent of varying length [26]. The complexes are reported to act as good olefin polymerization catalysts in the presence of MAO.52,53... 

Lanthanides as components in non-oxide systems As halides With co-catalysts for olefin polymerization in mixed halides for oxychlorination as supports... 

Lanthanides in homogeneous systems As organometallics As cerium(IV) salts As coordination complexes As nitrates, chlorides, alkoxides etc. For olefin polymerization For olefin hydrogenation For free radical polymerization For Diels-Alder reactions For olefin polymerization In organic synthesis... 

However, there is still a lot to do. The chemistry of lanthanide carbonyl and olefin complexes, and the complexes containing a lanthanide to transition metal bond and/or a lanthanide to lanthanide bond is still underdeveloped. To fully utilize these new aspects of reductive chemistry clever approaches will be needed. The development of highly active activatorless olefin polymerization catalysts and chiral versions of these families of complexes, and the catalysts for Cl chemistry are still the challenges. So, organolanthanide chemistry will continue to be an attractive field for organometallic chemists and there are many opportunities for the future. 

The charge of the Cp2M(R)" species is probably not the critical feature for olefin polymerization activity. Rather, the high polymerization activities observed for neutral group 3 and lanthanide Cp 2M(R) complexes... 

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. 

Olefin Polymerization Reactions Catalyzed by Lanthanide Amidinates... 

Smooth, but one-way, mechanistic crossover from olefin polymerization to group-transfer polymerization is possible with lanthanocene catalysts, since insertion of an acrylate into the propagating metal alkyl to form an enolate is energetically favorable. Block copolymers of ethylene with MMA, methyl acrylate, ethyl acrylate, or lactones have been prepared by sequential monomer addition to lanthanide catalysts and exhibit superior dyeing capabilities. However, the reverse order of monomer addition, i.e., (meth)acrylate followed by ethylene, does not give diblocks since the conversion of an enolate (or alkox-ide) to an alkyl is not favored. Therefore, although... 

There is an extensive chemistry of lanthanide metal-cyclopen-tadienyl complexes containing alkoxo ligands. Such species are, for example, very useful for olefin polymerization. For a recent review, see Yasuda, H. lhara, E. Adv. Polyw. Sci. 1997, 133, 53. 

Other active single-site early transition-metal-based catalysts for nonpolar monomers correspond to different bis-cyclopentadienyl group 3 and lanthanide complexes, such as L2MR (M = Sc, Y, La, Nd, Sm, Lu R = alkyl or H). Usually, these systems do not require the activator component to generate high activity catalysts for olefin polymerizations [3],... 

The polymerization of 1,3-dienes (e.g., 1,3-butadiene and isoprene) with Ziegler-Natta catalysts began in 1954, soon after the first results obtained in a-olefin polymerization since then many transition metal and lanthanide catalysts have been examined and several stereoregular diene polymers have been obtained [30, 31], 1,3-Dienes can generate several types of polymers having different stmctures trans-1,4 cis-1,4 1,2 and, in the case of asymmetric monomers (e.g., isoprene), 3,4. Stereoregular 1,2- or 3,4-polydienes may also exhibit iso- or syndiotacticity. (Figure 11.1). 

Group NIB and f-BIOCk Metallocenes. The need for expensive cocatalysts has always hampered the development of metallocene catalysts for olefin polymerization. It was recognized early on that substitution of the Group IVB metal with a lanthanide or Group IIIB element in the -1-3, state would represent a cocatalyst-free analogue of the Kaminsky system. Active catalysts are indeed obtained from bis-Cp lanthanocenes and yttrium- and scandium-based congeners. The lutetium dimer 29 has an activity of >7 kg/mmol(Lu)/h/atm for ethylene polymerization in cyclohexane (95). (This remarkable compound can also break the C—H bonds of alkanes.)... 

Interestingly, the first NHC complexes were reported with chromium (0) carbonyl by Ofele in 1968. Relatively few NHC early-transition metal complexes were then reported in the 1990s and this number steadily increased over the past decade. This subject is now mature moreover, the coordination chemistry of NHC has been investigated with alkali metals, alkaline earth metals, lanthanides or group 13-15 metals. Applications of these NHC complexes in catalysis now include, most notably, olefin polymerization or ring-opening polymerization of cyclic esters. Some of these complexes display high activity and selectivity and, in some instances, may compete with the best systems in the field. 

The insertion of alkenes into M-H bonds has been examined in Chap. 4. This reaction is very important because, it leads to the dimerization, oligomerization and polymerization of alkenes. It is broad and concerns not only transition metals, but also main-group metals (group 13 Lewis acids), lanthanides and actinides. For instance, AlEt3 is an excellent initiator of olefin polymerization. This reaction can also be considered as the hydrometallation or the hydroelementation of an olefin, and stoichiometric examples have been shown. If the element E does not have the property of a Lewis acid allowing olefin pre-coordination onto a vacant site and thus facilitating insertion, the insertion reaction is not possible without a catalyst. 

ScCp 2(CH3)] stable (but reactive) 14-electron complex (classic structure also with the lanthanides, these complexes being initiators of olefin polymerization)... 

---