Advances in Transition-Metal-Catalyzed Synthesis of Alkyne Polymers

The development of transition-metal-catalyzed reactions has remarkably facilitated the synthesis and applications of alkyne polymers of diverse structures and functions. Classical synthetic strategy of alkyne polymers based on acetylenic monomers includes: (1) acetylenic bond activation that leads to polycouplings; (2) carbon-carbon triple bond activation by metal carbynes/carbenes that leads to metathesis polymerizations. Recently, our group introduced a third mode based on copper-mediated propargylic bond activation of propargylic electrophiles, which generates allenyl copper species as key intermediates. The allenyl copper complex is involved in the in situ formation and chain-growth polymerization of [n]cumulene (n=3, 5), which eventually affords a unique alkyne backbone with carbon-carbon triple bonds spaced by two sp(3) carbons with exclusive regioselectivity. This article serves to describe recent developments of transition-metal-catalyzed synthesis of alkyne polymers based on polycouplings, metathesis, and propargylic activation, respectively. In particular, the chain-growth methods in each category are emphasized from a mechanistic perspective because of their potential in controlling the molecular weight and distribution, end groups, sequences, topology of the resulting alkyne polymers. This includes the catalyst transfer Sonogashira-type polycoupling, the ring-opening alkyne metathesis polymerization of strained alkynes, metathesis and metallotropy polymerization, and the emerging copper-catalyzed condensation polymerization of propargylic electrophiles developed by our group. The synergy between organometallic chemistry and synthetic polymer chemistry provides important driving force for both fields. [GRAPHICS] .