Catalyst precursors for polymerization

When a chiral ansa-type zirconocene/MAO system was used as the catalyst precursor for polymerization of 1,5-hexadiene, an main-chain optically active polymer (68% trans rings) was obtained84-86. The enantioselectivity for this cyclopolymerization can be explained by the fact that the same prochiral face of the olefins was selected by the chiral zirconium center (Eq. 12) [209-211]. Asymmetric hydrogenation, as well as C-C bond formation catalyzed by chiral ansa-metallocene 144, has recently been developed to achieve high enantioselectivity88-90. This parallels to the high stereoselectivity in the polymerization. 

The use of palladium(II) sulfoxide complexes as catalyst precursors for polymerization has met with mixed results thus a report of a palla-dium(II) chloride-dimethyl sulfoxide system as a catalyst precursor for phenylacetylene polymerization suggests similar results to those obtained using tin chloride as catalyst precursor (421). However, addition of dimethyl sulfoxide to solutions of [NH fPdCh] decreases the activity as a catalyst precursor for the polymerization of butadiene (100). Dimethyl sulfoxide complexes of iron have also been mentioned as catalyst precursors for styrene polymerization (141). 

A bisiminylpyridine complex of iron that is a catalyst precursor for polymerizations that occur by 2,1-insertions. 

In this section we survey the use of metallocenes as catalyst precursors for polymerizations in which the predominant monomer is not ethylene or any a-olefin. The subject of metallocenes as initiators for the cationic polymerization of vinyl monomers is dealt with elsewhere. Except for styrene, true random copolymers of the monomers in this section with alkenes are not produced because the mechanisms for polymerization of the non-olefins differ greatly from that operating in Sinn-Kaminsky catalysis. 

The alcoxycarbene [W(=CMeOEt)(CO)5] is used as a catalyst precursor for polymerization of cyclopentene, in the presence of the cocatalyst EtAlCl2 [34] but other carbene complexes e.g. [W(=CPh2)(CO)5], can be used without a cocatalyst for the same reaction [35]. 

The patent literature contains several references to the use of sulfoxide complexes, usually generated in situ, as catalyst precursors in oligomerization and polymerization reactions. Thus, a system based upon bis(acrylonitrile)nickel(0> with added Me2SO or EtgSO is an effective cyclotrimerization catalyst for the conversion of butadiene to cyclo-1,5,-9-dodecatriene (44). A similar system based on titanium has also been reported (407). Nickel(II) sulfoxide complexes, again generated in situ, have been patented as catalyst precursors for the dimerization of pro-pene (151) and the higher olefins (152) in the presence of added alkyl aluminum compounds. 

Fig. 11 Schematic representation for the in situ formation of the catalyst precursor with polymeric ligands of the type PG(C5-1,2DMI-TPPMS)i.0...

Well-defined ruthenium vinylidene complexes are efficient catalyst precursors for the ring-opening metathesis polymerization (ROMP) of cyclic olefins (Fig. 9). Most of them are neutral 16-electron complexes of the type RuC12(L)2(=C=CHR) (LI) [65-68] and the more active precursors contain... 

Group 4 elements (e.g., Ti, Zr) are used as typical catalyst precursors for olefin polymerization and serve as potent cationic components for polymer chain growth with the aid of aluminum (e.g., MAO) or boron co-catalysts. It would be more efficient and convenient if organoaluminum cations were used to polymerize olefins. From this viewpoint, following an earlier precedent with two-coordinate cations (Equation (98)),319,320 some three-coordinate organoaluminum cations hold promise, and their ability to promote polymerization of ethylene or terminal olefins is now... 

The oligomerization of olefins is mostly catalyzed by cationic complexes which are very soluble in ionic liquids. The Pd-catalyzed dimerization of butadiene [36] and the Ni-catalyzed oligomerization of short-chain olefins [5, 37], which is also known as the Difasol process [1 d] if chloroaluminate melts are used, can be mn in imidazolium salts 1 [38, 39]. Here, the use of chloroaluminate melts and toluene as the co-solvent is of advantage in terms of catalyst activity, product selectivity, and product separation. Cp2TiCl2 [6] and TiCU [40] in conjunction with alkylaluminum compounds were used as catalyst precursors for the polymerization of ethylene in chloroaluminate melts. Neither Cp2ZrCl2 nor Cp2HfCl2 was catalytically active under these conditions. The reverse conversion of polyethylene into mixtures of alkanes is possible in acidic chloroaluminate melts without an additional catalyst [41]. 

A series of 1- and 2-aryl substituted trichloro indenyltitanium complexes (ArInd)TiCl3 (Ar = Ph, ct-Naph, /3-Naph) have been synthesized and tested as catalyst precursors for the syndiospecific polymerization of styrene with MAO as a co-catalyst.409... 

Mono-Cp titanium derivatives show reactivity as catalyst precursors for olefin polymerizations, particularly for the polymerization of styrene and functionalized monomers. A review highlighting the developments in the design and applications of non-metallocene complexes, including mono-Cp derivatives, as catalyst systems for a-olefin polymerization has appeared.440 Titanium complexes bearing Cp in addition to chloro ligands and activated by aluminum... 

A monograph including complexes with Cp-amido ligands has recently been published.676 The role of the group 4 Cp-amido derivatives as catalyst precursors for olefin polymerization has been reviewed.677 A review highlighting the... 

The monoalkoxo complexes CpTiCl2(OR)(R = methoxyethyl, methoxypropyl, methoxy-isopropyl, o-methoxyphe-nyl, tetrahydrofurfuryl) have been synthesized, characterized and, when activated with MAO, tested as catalyst precursors for the syndiospecific polymerization of styrene.853,854... 

The unbridged bis(2-methylbenz[/]indenyl) and the mixed ring Gp 2-methylbenz[V indenyltitanium complexes have been synthesized and evaluated as catalyst precursors for the polymerization of ethylene and propylene (Scheme 441). They exhibit low activity for the olefin polymerization when activated with either MAO or trityl borate.1054... 

The base-free dimethyl Sc complex 121 was a highly active catalyst precursor for ethylene polymerization under B(C6F5)3, trityl borate, or methylaluminoxane (MAO)-type activation. The catalytic activity of 121 was similar to those observed of Group 4 metallocene complexes [81]. Generally, cationic scandium complexes are believed to be the active species. Activation of the catalyst was studied by reacting 120 and 121 with various equivalences of B(C6F5)3. The monomeric bulky rBu-substituted dimethyl complex 121 reacted with 1 equiv of B(C6F5)3... 

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