Ru-based metathesis catalysts employed in cyclopolymerization (CP) of 1,6-heptadiyne derivatives have promoted regioselective α-addition to alkynes, forming various conjugated polyenes containing exclusively five-membered repeat units. Recently, we discovered that a new chelated Ru catalyst could promote regioselective β-addition to produce analogous polyenes containing six-membered rings with moderate to good β-selectivity. Since then, we have focused our research on pursuing more active and β-selective regiocontrol to produce conjugated polymers with excellent βselectivity, with a much broader range of monomers. Herein, we demonstrate highly β-selective CP by combining a new dithiolate-chelated Ru-based catalyst with weakly coordinating pyridine additives, which significantly enhance the conversion and β-selectivity. An in-depth mechanistic investigation by 1 H NMR revealed a prominent role for the additives, which improve the stability of the propagating carbene.

An unsaturated polymer’s cis/trans-olefin content has a significant influence on its properties. For polymers obtained by ring-opening metathesis polymerization (ROMP), the cis/trans-olefin content can be tuned by using specific catalysts. However, cis-selective ROMP has suffered from narrow monomer scope and lack of control over the polymerization (giving polymers with broad molecular weight distributions and prohibiting the synthesis of block copolymers). Herein, we report the versatile cis-selective controlled living ROMP of various endo-tricyclo­[4.2.2.02,5]­deca-3,9-diene and various norbornene derivatives using a fast-initiating dithiolate-chelated Ru catalyst. Polymers with cis-olefin content as high as 99% could be obtained with high molecular weight (up to M n of 105.1 kDa) and narrow dispersity (<1.4). The living nature of the polymerization was also exploited to prepare block copolymers with high cis-olefin content for the first time. Furthermore, owing to the successful control over the stereochemistry and narrow dispersity, we could compare cis- and trans-rich polynorbornene and found the former to have enhanced resistance to shear degradation.

On the basis of a combined experimental and computational study, a novel method for preparing fully conjugated polyenynes via cascade metathesis and metallotropy (M&M) polymerization of various multialkynes is developed. DFT calculations elucidate the detailed mechanism of the metallotropic 1,3-shift, which is a key process of M&M polymerization. An α,β-(C,C,C)-agostic interaction stabilizing the metallacyclobutadiene transition state is found to be critically important for the successful polymerization with excellent specificity. The polymerization efficiency displayed by the tetrayne monomer is controlled by the steric demands of its substituents, and more complex hexayne monomers can be successfully polymerized to give access to highly conjugated polyenynes via a series of intramolecular metathesis and metallotropic shift cascade reactions. Furthermore, living polymerization led to the synthesis of block copolymers consisting of fully conjugated polyenyne backbones. The implementation of pentayne monomers provides polyenynes with successive C–C triple bonds via consecutive metallotropic 1,3-shift. In short, the design of multialkynes enables the preparation of diverse conjugated polyenyne motifs via selective M&M cascade reactions.

Herein, we demonstrate the first example of living β-selective CP by rational engineering of the steric factor on monomer or catalyst structures, along with a mechanistic investigation by in situ kinetic studies using 1H NMR spectroscopy.