Transition metal, catalysis polymerization

The first example of homogeneous transition metal catalysis in an ionic liquid was the platinum-catalyzed hydroformylation of ethene in tetraethylammonium trichlorostannate (mp. 78 °C), described by Parshall in 1972 (Scheme 5.2-1, a)) [1]. In 1987, Knifton reported the ruthenium- and cobalt-catalyzed hydroformylation of internal and terminal alkenes in molten [Bu4P]Br, a salt that falls under the now accepted definition for an ionic liquid (see Scheme 5.2-1, b)) [2]. The first applications of room-temperature ionic liquids in homogeneous transition metal catalysis were described in 1990 by Chauvin et al. and by Wilkes et ak. Wilkes et al. used weekly acidic chloroaluminate melts and studied ethylene polymerization in them with Ziegler-Natta catalysts (Scheme 5.2-1, c)) [3]. Chauvin s group dissolved nickel catalysts in weakly acidic chloroaluminate melts and investigated the resulting ionic catalyst solutions for the dimerization of propene (Scheme 5.2-1, d)) [4]. 

Optically active polymers are potentially very useful in areas such as asymmetric catalysis, nonlinear optics, polarized photo and electroluminescence, and enantioselective separation and sensing.26 Transition metal coupling polymerization has also been applied to the synthesis of these polymers.27 For example, from the Ni(II)-catalyzed polymerization, a regioregular head-to-tail polymer 32 was obtained (Scheme 9.17).28 This polymer is optically active because of the optically active chiral side chains. 

Transition metal coupling polymerization has also been used to synthesize optically active polymers with stable main-chain chirality such as polymers 33, 34, 35, and 36 by using optically active monomers.29-31 These polymers are useful for chiral separation and asymmetric catalysis. For example, polymers 33 and 34 have been used as polymeric chiral catalysts for asymmetric catalysis. Due... 

The mechanism for hydrosilylation in Figs. 6 and 7 clearly has much in common with suggestions regarding homogeneous transition metal catalysis for other processes involving olefins, such as hydrogenation, isomerization, the oxo reaction, and oligo- and polymerization. 

Polycondensation pol5mers, like polyesters or polyamides, are obtained by condensation reactions of monomers, which entail elimination of small molecules (e.g. water or a hydrogen halide), usually under acid/ base catalysis conditions. Polyolefins and polyacrylates are typical polyaddition products, which can be obtained by radical, ionic and transition metal catalyzed polymerization. The process usually requires an initiator (a radical precursor, a salt, electromagnetic radiation) or a catalyst (a transition metal). Cross-linked polyaddition pol5mers have been almost exclusively used so far as catalytic supports, in academic research, with few exceptions (for examples of metal catalysts on polyamides see Ref. [95-98]). 

Conjugated dienes are among the most significant building blocks both in laboratories and in the chemical industry [1], Especially, 1,3-butadiene and isoprene are key feedstocks for the manufacture of polymers and fine chemicals. Since the discovery of the Ziegler-Natta catalyst for the polymerizations of ethylene and propylene, the powerful features of transition metal catalysis has been widely recognized, and studies in this field have been pursued very actively [2-7]. 

Transition metal catalysis plays a key role in the polyolefin industry. The discovery by Ziegler and Natta of the coordination polymerization of ethylene, propylene, and other non-polar a-olefins using titanium-based catalysts, revolutionized the industry. These catalysts, along with titanium- and zirconium-based metallocene systems and aluminum cocatalysts, are still the workhorse in the manufacture of commodity polyolefin materials such as polyethylene and polypropylene [3-6],... 

Primary and secondary aliphatic amines can be linked to polymeric supports by acid-labile linkers or by linkers sensitive to nucleophiles. Linkers cleavable by light or by transition metal catalysis have also been described. The main types of linker for amines are sketched in Figure 3.24. 

Ring-opening polymerization is one of the most important applications of SCBs in organic chemistry. Polymerization of SCBs, which gives rise to carbosilane polymers, has been carried out thermally, by transition metal catalysis, or, most commonly, by anionic initiation. Thermal polymerization is rare, however, and is not covered in this chapter. For leading references into thermal polymerization of SCBs, refer to <1996CF1EC-II(1B)867> and <1995COMC-II(2)50>. 

If the metal cation is too electrophilic, CO coordination will be too strong, possibly by coordination via its oxygen atom, and CO will act as a poison rather than participating in the polymerization [40], The moderate electrophilicity of Pd" catalysts makes them tolerant also to a variety of heteroatom functionalities in the olefin substrate. In this respect, polyketone catalysis can have a wider applicability than early transition metal catalysis of polyolefins, which is highly intolerant of functional groups. 

As early as 1948, Reppe et al. reported the discovery of the cyclic polymerization of acetylene to cyclooctatetraene (eq. (29)) using nickel catalysts [84]. This discovery represented a true landmark in transition metal catalysis. 

Camurati, I. Fait, A. Piemontesi, F. Resconi, L. Tartarini, S. Transfer and Isomerization Reactions in Propylene Polymerization with the Isospecific, Highly Regiospecific raz-Me2C(3-/-Bu-l-Ind)2ZrC12/MAO Catalyst. In Transition Metal Catalysis in Macromolecular Design ACS Symposium Series Boffa, L. S., Novak, B. M., Eds. American Chemical Society Washington, DC, 2000 Vol. 760, 174. 

Multiple halogen compounds FI-31158 and FI-32328 seem interesting to attest the chemoselectivity of transition-metal catalysis, and the CF3 and the aromatic bromide therein, respectively, remain intact during the living polymerizations to afford a-end functions, though their utility might be limited. 

Conceptually similar constrained geometry catalysts feature distorted cyclo-pentadienyl/o-donor ligands and have found widespread use in early transition metal catalysis, most notably polymerization." In these cases, the bite angle of the cyclo-pentadienyl (Cp)-metal-amido is compressed by -25-30° compared to unstrained metallocenes (Figure 12)." ... 

R. Schrock as an "Erwin Schrddinger Fellow". In 1995 he accepted a position as an Assistant Professsor at the University of Innsbruck, where he finished his Habilitation in Macromolecular Chemistry in 1998. Since 1998, he has held a faculty position as an Associate Professor. His research interests focus on transition-metal-catalyzed polymerizations, heterogeneous polymeric systems and their applications in the areas of heterogeneous catalysis, as well as separation and life sciences. 

This section focuses on transition-metal-catalyzed polymerizations in SCCO2, which are related to the other homogeneous catalysis reactions in SCCO2. A variety of metal-catalyzed polymerizations in SCCO2 have been demonstrated. 

Ouchi M, Terashima T, Sawamoto M (2008) Precision control of radical polymerization via transition metal catalysis from dormant species to designed catalysts for precision functional polymers. Acc Chem Res 41 1120-1132... 

Keywords Polysilanes / Polymerization / Transition Metal Catalysis... 

No successful example has been reported so far using a TSA in a dynamic combinatorial approach to transition metal catalyst selection. However, inspired by enzymes and molecular cages, molecularly imprinted polymers were successfully developed by WuUF et al. and in a small number of cases directed towards transition metal catalysis [22]. Cavities as biomimetic catalysts are created by generation of polymeric materials in the presence of a TSA as a template, which is removed after polymerization. In the presence of the substrate, the incorporation of the catalyst precursor leads to high activities, the transition state being stabilized by the polymeric cavities. 

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