Palladium catalysts polymer synthesis

Triphenylamine derivatives are known to be efficient hole transport materials and are widely used in organic light-emitting devices. Thelakkat et al. reported the synthesis of a 2,2-bipyridine ligand capped with polyfvinyl-triphenylamine) at both ends.97 The polymer chain was synthesized by the atom transfer radical polymerization of 4-bromostyrene using 4,4-bis (chloromethyl)bipyridine as the initiator (Scheme 18). The bromide groups were then replaced by diphenylamine in the presence of palladium catalyst. Polymer 33 was then obtained by the metalation reaction. 

At about die same time, die application of the Suzuki coupling, the crosscoupling of boronic acids widi aryl-alkenyl halides in die presence of a base and a catalytic amount of palladium catalyst (Scheme 9.12),16 for step-growth polymerization also appeared. Schliiter et al. reported die synthesis of soluble poly(para-phenylene)s by using the Suzuki coupling condition in 1989 (Scheme 9.13).17 Because aryl-alkenyl boronic acids are readily available and moisture stable, the Suzuki coupling became one of die most commonly used mediods for die synthesis of a variety of polymers.18... 

Beilina F, Carpita A, Rossi R (2004) Palladium catalysts for the Suzuki Crosscoupling reaction an overview of recent advances. Synthesis 2419-2440 Bhattacharyya SJ (2000) Polymer-supported reagents and catalysts recent advances in synthetic applications. Comb Chem High Throughput Screening 3 65-92... 

An excellent method for the synthesis of 1,3-diene from polymer-supported alkyne and olefin (Scheme 16) has also been reported. Reaction of polymer-supported alkyne 44 and alkene 47a in the presence of Ic gives polymer-supported 1,3-diene 45a, which is treated with a palladium catalyst in the presence of a nucleophile for cleavage from the polymer to give 46a in 66% yield. In a similar manner, 46b, 46c, and 46d are obtained from polymer-supported alkyne 44 in high yields. These results indicate that various kinds of nucleophiles are introduced at the diene allylic position corresponding to the propargylic position in 44 (Scheme 16). 

J. A. Bmce, T. Murahashl, and M. S. Wrighton, Synthesis and characterization of structured interfaces for hydrogen generation. Study of an N, N -dialkyl-4, 4-bipyridinium redox polymer/palladium catalyst system, J. Phys. Chem. 86, 1552, 1982. 

The imidazole, benzoxazole, and benzthiazole derivatives in Table 7-3 are rather moisture-sensitive.92 On the whole, however, the heteroarylstannanes show the same reactions that characterise the homoarylstannanes. With a palladium catalyst, they undergo coupling112 and cross-coupling reactions68 and indeed much of the recent interest in the heteroarylstannanes stems from their applications in the Stille reaction (see Section 22.2). One aspect of this is the synthesis of oligomers and polymers or copolymers, for example by the cross-coupling of 2,5-distannylthiophene with a 1,4-diiodo-arene.113,114... 

The synthesis of alternating copolymers from carbon monoxide (CO) and olefins using palladium catalysts is currently an area of intense research. In cases where a-olefins are used, the regiochemistry (head/tail orientations) and stereochemistry (tacticity) of olefin insertion have a strong influence on the physical and mechanical properties of the polymers. Unlike regioregular a-olefins homopolymers, these copolymers have a directionality along the polymer backbone due to the incorporation of CO. Therefore isotactic, regioregular CO/a-olefin polymers are chiral by virtue of their main-chain stereochemistry (Scheme 11). 

Rapid and efficient Suzuki coupling of protoxygencol has been developed using polymer-supported palladium catalysts under microwave conditions at 110 °C within 10 min. in the synthesis of various benzolidines [15]. Radical cyclization of resin-bound N-(2-bromophenyl)acrylamides using Bu3SnH proceeded smoothly in DMF or toluene as solvent under the action of microwave irradiation for preparation of 2-oxindoles as illustrated in Scheme 10.9. This method is superior to conventional solution synthesis [16]. 

Synthesis of conjugated p-phenylene ladder polymers by means of a microwave-assisted reaction has been achieved by Scherf et al. (Scheme 14.35) [72]. The polymerization reactions were performed in THE solution at 130 °C in the presence of palladium catalyst with phosphine ligands with irradiation in a single-mode micro-wave reactor for 11 min. Compared with conventional thermal procedures, the reaction time was reduced from days to a couple of minutes and molecular weight distributions ( PDI ca 1.8) of the polymers were changed substantially. 

Nearly 40 years have evolved between the first discovery by Reppe of transition-metal-catalyzed CO/ethene copolymerization and the discovery in 1983, at Shell, of a class of highly active, high yield palladium catalysts for the synthesis of high molecular weight, perfectly alternating CO/ethene copolymers [PK-E, Fig. 1], This class of catalysts is also active for the co- and terpol5unerization of CO with alkenes other than ethene, both simple aliphatic and heteroatom functionalized, thus providing access to a family of completely new polyketone polymers. 

---