Cross-coupling polymerization metathesis

CRM, see Cyclopentadienyl ring metathesis Cross-coupling polymerization miscellaneous reactions, 11, 678 overview, 11, 653-690... 

Suzuki-Miyaura cross-coupling polymerization of 1,4-bis((Z)-2-bromovinyl)benzenes with aryl-bis-boronic acids. The interest has been in an alternative approach, where rather than building a PPV with a pre-ordained stereochemistry, a postpolymerization yyn-selective reduction on a poly(phenylene ethynylene) (PPE) is used [125]. This scheme has the advantage that high molecular weight PPEs can be synthesized using either Pd-catalysis or alkyne metathesis. This route could also potentially allow for the access to an additional array of PPVs that are uniquely accessible from PPEs. The transformation of the triple bonds in PPEs and other acetylene building blocks to alkenes has considerable potential. 

Since one of the substrates is a cyclic alkene there is now the possibility of ring-opening metathesis polymerisation (ROMP) occurring which would result in the formation of polymeric products 34 (n >1). Since polymer synthesis is outside the scope of this review, only alkene cross-metathesis reactions resulting in the formation of monomeric cross-coupled products (for example 30) will be discussed here. 

The PPEs [14, 35, 36], which are dehydrogenated analogs of the poly(p-phenylene vinylene) s, display desirable optoelectronic properties that have found extensive use as emissive materials [37, 38]. PPE preparation is dominated by the Sonogashira Pd/Cu-catalyzed cross-coupling of aryl haUdes and terminal alkynes [39]. However, polymerizations under these conditions rarely achieve a high molecular weight, and defects such as diyne formation and alkyne crosshnking in the polymer backbone are endemic [14, 40]. Alkyne metathesis was envisioned as a complementary method to PPE synthesis, with much success. 

Abstract Applications of five-membered ring products as catalysts in cyclometalation reactions inclnde chiral reactions, metathesis reactions, cross-coupling reactions, and polymerization reactions. Other reactions include reductions, Michael addition reactions, dehydrogenations, Diels-Alder reactions, and hydrogenations. 

An Organometallic Com pound That Occurs Naturally Coenzyme B,2 591 Organocopper Reagents 592 Palladium-Catalyzed Cross-Coupling 595 Homogeneous Catalytic Hydrogenation 597 Olefin Metathesis 600 Ziegler-Natta Catalysis of Alkene Polymerization 603 Summary 606 Problems 608... 

Asymmetric ring opening metathesis reactions can also be performed.67-66 In these cases, it is common for the reaction to be coupled with a cross metathesis or other reaction to avoid polymerization of the product.51 The catalysts are constantly being improved to provide higher selectivities and faster reactions. The catalyst 35 is recyclable and air-stable (Scheme 28.24).60-71... 

Linear PPE-PPV hybrids of the meta and the para varieties (6, 61-64) have been produced by Sonogashira coupling and alkyne metathesis. These polymers show properties that are intermediate between those of the PPVs and the PPEs. Klemm et al. have shown that Horner reactions of suitable substrates lead to linear PPE-PPV hybrids, although the degree of polymerization is not particularly high [98]. The motivation behind these synthetic efforts is to combine the favorable hole injection properties of the PPVs with the blue emission, the stability, and the high fluorescence quantum yields of the PPEs. Several attempts have been made to obtain efficient LED action, but 62, the best one, so far shows a luminance of 147 cd/m at 602 nm, at 14 V, which is not very impressive compared with the numbers that are obtained for PPVs [99-102]. Cross-conjugated PPEs were first synthesized by Bunz et al. (63, 64) and are useful as photodiode-active materials [102]. The dialkylamino substituents in... 

Keywords silylative coupling, silylation, cross-metathesis, polymerization, vinylsilanes, catalysis... 

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