The History of Palladium-Catalyzed Cross-Couplings Should Inspire the Future of Catalyst-Transfer Polymerization

Abstract

Conjugated polymers are the workhorse materials in organic electronics, a field that is rapidly growing to encompass energy storage devices such as supercapacitors and batteries. The highest-performing materials today have incredibly diverse structures and are accessed via step-growth polymerizations. This method results in limited control over the polymer’s molecular weight, sequence, and dispersity, all of which can significantly impact device performance. The discovery of catalyst-transfer polymerization (CTP) in 2004 was predicted to change this landscape. Instead, nearly 14 years later, the CTP scope remains mostly limited to polymerizing small, electron-rich monomers. There is a pronounced gap between the rich array of structures utilized in organic electronics and what can be polymerized in a living, chain-growth fashion via CTP. Here, we suggest that palladium precatalysts could bridge this gap based on their huge versatility in the small-molecule cross-coupling literature. We highlight specific ancillary ligands from the small-molecule literature that we anticipate are candidates for enabling diverse conjugated polymer syntheses based on nearly a decade of research into the CTP mechanism. In addition, we describe several recent promising examples of CTP mediated by Pd precatalysts that serve as inspiration for the future. We present this Perspective as a call-to-action to advance organic electronics with CTP.

Photocontrolled Synthesis of n‐Type Conjugated Polymers

“…To gain control over molecular weight and architecture, researchers have developed catalyst‐transfer polycondensation (CTP), a living polymerization relying on Ni and Pd catalysts that associate strongly with the growing polymer chain. CTP has been primarily optimized for p‐type systems . Nevertheless, in all these examples, synthetic methods for CPs rely on mechanisms and transition‐metal catalysts first developed for small‐molecule sp 2 –sp 2 cross‐coupling reactions.…”

A General and Air‐tolerant Strategy to Conjugated Polymers within Seconds under Palladium(I) Dimer Catalysis

“…Again, performing the polymerization open to the laboratory atmosphere had no impact (see entry 6). [23] With independence from the nature of the side chain demonstrated, we next explored the compatibility of the Pd Ibased polymerization with electronically varied motifs,more specifically heteroatoms.I nt his context, ar epresentative materials class is polycarbazole (3). [15d] Theneed for relatively high palladium loading in the former case might stem from the fact that an oxidative addition complex, that is, [(PtBu 3 )Pd(Ph)Br],w as utilized as catalyst.…”

“…[15d] Theneed for relatively high palladium loading in the former case might stem from the fact that an oxidative addition complex, that is, [(PtBu 3 )Pd(Ph)Br],w as utilized as catalyst. [25] Pd-based Suzuki coupling [with ac atalyst system of Pd 2 (dba) 3 and P(o-tol) 3 ]a nd Stille-based polymerization were also previously used. [22] As such, the Pd I protocol offers much faster polymerization (30 seconds vs.3 0min) using ar obust and air-stable catalyst and requiring lower loadings in Pd.…”

Investigation of Bimetallic Nickel Catalysts in Catalyst‐Transfer Polymerization of π‐Conjugated Polymers

“…[23] Discussion on the critical factors that enable controlled polymerizations in CTP has been thoroughly detailed in reviews. [24][25][26] Interestingly, one area that has not been relatively explored at all in CTP, and may be useful, is multimetallic cooperative catalysis.Multimetallic cooperative catalysts have been employed to improve the quality of olefin [27][28][29] and epoxide [30] polymers (Figure 1). In these studies, the geometry of the bimetallic catalysts and the proximity of the metal centers were suggested to have critical influence on catalytic rates, branching, chain transfer, and control over molecular weight and dispersity.…”

“…[23] Discussion on the critical factors that enable controlled polymerizations in CTP has been thoroughly detailed in reviews. [24][25][26] Interestingly, one area that has not been relatively explored at all in CTP, and may be useful, is multimetallic cooperative catalysis.…”