Palladium‐Catalyzed Chain‐Growth Polycondensation of AB‐type Monomers: High Catalyst Turnover and Polymerization Rates

Abstract

Chain-growth catalyst-transfer polycondensations of AB-type monomers is a new and rapidly developing tool for the preparation of well-defined p-conjugated (semiconducting) polymers for various optoelectronic applications. Herein, we report the Pd/PtBu 3 -catalyzed Negishi chain-growth polycondensation of AB-type monomers, which proceeds with unprecedented TONs of above 100 000 and TOFs of up to 280 s À1 . In contrast, related AA/BB-type step-growth polycondensation proceeds with two orders of magnitude lower TONs and TOFs. A similar trend was observed in Suzuki-type polycondensation. The key impact of the intramolecular (vs. intermolecular) catalyst-transfer process on both polymerization kinetics and catalyst lifetime has been revealed.p-C onjugated (semiconducting) polymers have become an important class of materials for applications in polymer solar cells, field-effect transistors, and light emitting diodes. [1] p-Conjugated polymers are generally produced by step-growth polymerizations, most often by Pd-catalyzed Stille [2] and Suzuki [3] polycondensations with the so-called AA/BB approach. [4] p-Conjugated polymers synthesized in such a way frequently suffer from a low degree of control over molecular weight (MW) which is undesirable for optoelectronic applications. Another drawback of step-growth Stille and Suzuki polycondensations is that they are relatively slow processes because of the moderate nucleophilicity of tin-and boron-organics. With these methods, synthesis of high MW polymers (which are especially attractive for applications) [5] usually requires long reaction times, high temperatures, and high loadings of expensive Pd catalysts. [2] The formation of toxic byproducts is another drawback inherent to Stille polycondensation. On the other hand, Negishi type polycondensation, which utilizes non-toxic and strongly nucleophilic zinc-organic-based monomers, is a promising technique for industrial-scale production. [6] Impressive progress was achieved in the last decade in the development of new, more efficient Pd catalysts for cross-couplings of small molecules. [6] Particularly, it was demonstrated that the use of bulky and electron-rich ligands enables, in many cases, cross-couplings to proceed under mild conditions, with low catalyst loadings and involving otherwise inactive electrophiles. [7] Turnover numbers (TONs) [8] above 100 000 where demonstrated in Suzuki, Negishi, and Heck cross-couplings, making them attractive for commercial applications. [9] Surprisingly, mechanistically related polycondensations underwent little improvement since their discovery. [2,3] Chain-growth catalyst-transfer polycondensations of ABtype monomers is a new and rapidly developing alternative for the preparation of well-defined conjugated homo-, gradient-, and block-copolymers. [10] Unlike the situation with step-growth polycondensations, promising results were achieved in chain-growth polycondensations initiated by newgeneration catalysts. [10][11][12] Particularly, it was shown that Pd/ PtBu 3 is an efficient in...

Transformation of Step-Growth Polymerization into Living Chain-Growth Polymerization

“…However, the polymerization involved chain termination and did not show living polymerization nature. 94 Similar behavior was observed in polymerization of naphthalenediimide− dithiophene monomer 98 and the perylenediimide−dithiophene monomer 99 with the same Pd catalyst.…”

Poly(phenylene ethynylene) Conjugated Polyelectrolytes Synthesized via Chain-Growth Polymerization

“…This suggests that the catalyst is limited to a turnover number of ∼10 under the conditions of the reactions reported here. 36 However, the good news is that the dispersity of the chain-growth samples is considerably less than for the samples prepared by the step-growth methods (Table 1). Further, we purposely synthesized a step-growth polymer with DP ∼10 (sg-AABB2) to allow comparison with the chain-growth polymers of comparable DP.…”

Anion-Radical Polymerization of Sulfur- and Selenium-Substituted N-Type Conjugated Polymers

“…It is worth noting that we observed trace low-order oligomers for Pd/P(t-Bu) 3 -catalyzed polymerization of both S1-Th and S2-Th. Since Pd/P(t-Bu) 3 is known to promote rapid albeit uncontrolled polymerization, 52 it is likely that some degree of Pd/P(t-Bu) 3catalyzed polymerization occurs prior to sulfur poisoning of the palladium catalyst. While further catalyst optimization may allow polymer propagation for acceptor units with high electron affinities, it would be beneficial to avoid thionyl groups to eliminate the risk of sulfur poisoning in future acceptor unit optimization.…”