New advances in chain-growth polymerization using palladium intermediates

A team of researchers at Peking University has achieved stable chain-growth polymerization using propargyl/allenyl palladium intermediates, making it possible to synthesize complex polymers in a new way. The research was carried out by Zheng-Lin Wang and Rong Zhu as part of a joint project, with support from Beijing National Laboratory of Molecular Sciences (BNLMS), Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education, College of Chemistry and Molecular Engineering.

Chain-growth polymerization is a polymerization technique whereby monomer molecules are added one by one to a chain. First elaborated in the 1950s, this method is used to create a number of polymers with wide-ranging applications such as polyethylene (PE), polypropylene (PP) and polyvinyl chloride (PVC).

Since the late 1980s, synthetic organic chemistry has found numerous applications for substitution reactions involving allylic electrophiles that use a palladium catalyst. While they are structurally similar, catalysis using propargyl/allenyl electrophiles has been studied to a lesser extent. One possible explanation for this is that the additional π-bond in the intermediate drastically increases the complexity of the reaction.

While π-allyl catalysis always leads to allylation, nucleophilic trapping (an electron-rich species reacting with an intermediate) in propargyl/allenyl systems can occur via three palladium complexes, bringing associated changes to the substrate-catalyst combination. The σ-allenyl complex leads to allenylation (type A), the π-propargyl causes alkenylation (type B), and the σ-propargyl (type C) palladium complex brings about propargylation.

The main goal of the study was to overcome type B trapping, a side process that interrupts chain growth in polymerization using propargyl/allenyl electrophiles. In this scenario, the intermediate forms a π-propargyl palladium complex (type B), which is then rapidly consumed in side reactions — such as a second nucleophilic attack or β-hydride elimination — rather than continuing the polymer chain. While type B trapping is a common and often efficient pathway in palladium catalysis, it prevents the controlled addition of monomers required for chain-growth polymerization. The researchers identified a special allenylic electrophile known as vinylidenecyclopropane 1,1-dicarboxylate (VDCP) as a potential solution to the difficulty of supporting chain-growth reactions. The chemical can be synthesised in two steps from two widely available commodity chemicals: butyne-1,4-diol and malonate.

Experimental and computational evidence showed support for propargyl/allenyl palladium intermediates. Controlled ring-opening polymerization was achieved with the palladium catalyst, and VDCP selectively reacted via the σ-allenyl palladium complex (type A) as opposed to the more common π-propargyl pathway (type B). The material’s exceptional reactivity supported the precise synthesis of alkyne-backbone polymers, and the researchers were able to demonstrate the preparation of unsaturated macromolecules with advanced sequences and architectures

Palladium is a platinum group metal (PGM) prized across numerous industries for its unique applications, including its catalytic properties. Pd is one of the important metals in organic chemistry, where it is one of the most commonly used catalysts. This is the result of its unique ability to support the controlled formation of certain bonds, such as carbon–carbon (C–C) and carbon–heteroatom bonds, i.e. those involving heteroatoms such as nitrogen, oxygen and sulphur.

Complex polymers such as the aforementioned PE, PP and PVC have long been some of the most important synthetic polymers in the world, thanks to their cost-effectiveness, durability and versatility. They are used in piping, containers, insulation, consumer appliances, medical devices, fabrics, construction materials and much more. More recently, research is underway on new applications in the green economy. Conjugated polymers are a key material in organic photovoltaic cells, as well as a new generation of batteries and semiconductors. While these technologies are at an early stage, they could potentially make cutting-edge renewable technologies significantly more durable and affordable.

Source: https://www.nature.com/articles/s41467-025-57723-8