Living β-selective cyclopolymerization using Ru dithiolate catalysts.

Area of Science:

• Polymer Chemistry
• Organic Synthesis
• Catalysis

Background:

• Cyclopolymerization (CP) of 1,6-heptadiyne derivatives yields conjugated polyenes with five- or six-membered rings via α- or β-addition.
• Previous ruthenium (Ru)-based catalysts favored α-addition, limiting access to six-membered ring structures.
• Recent advancements achieved β-selective control but suffered from slow initiation and poor catalyst stability, hindering controlled polymerization.

Purpose of the Study:

• To develop a living β-selective cyclopolymerization method for synthesizing conjugated polyenes with six-membered rings.
• To achieve controlled polymerization by addressing issues of slow initiation and catalyst instability.
• To enable the synthesis of well-defined block copolymers using a broad range of monomers.

Main Methods:

• Rational engineering of steric factors in either the monomer or the ruthenium-based catalyst structure.
• Utilizing dithiolate-chelated Ru catalysts for β-selective addition.
• Employing in situ kinetic studies with ¹H NMR spectroscopy and pyridine additives for mechanistic investigation.

Main Results:

• Achieved living β-selective cyclopolymerization by imposing steric demands on monomers or catalysts.
• Demonstrated control over polymer molecular weight and narrow dispersities, tunable by catalyst loading.
• Successfully synthesized diblock and triblock copolymers across a wide range of monomers.

Conclusions:

• Steric engineering is crucial for enhancing catalyst stability and controlling initiation/propagation rates in β-selective CP.
• The developed method provides a robust platform for synthesizing precisely controlled conjugated polymers and block copolymers.
• This advancement expands the synthetic utility of cyclopolymerization for creating advanced polymer architectures.