Polycyclooctatetraene (polyacetylene) produced with a ruthenium olefin metathesis catalyst

Abstract

The area of highly conjugated organic polymers has commanded interest for quite some time. Polyacetylene (PA) is the (structurally) simplest conjugated organic polymer; however, its intractable nature has made its characterization quite difficult. The first successful PA film was produced in 1971 by Shirakawa and Ikeda from acetylene monomer and a highly concentrated Ziegler–Natta catalyst. Over the last 30 years, several methods have been introduced which allow for the synthesis of a pre-cursor polymer that can subsequently be transformed into PA. Unfortunately, many of these techniques either involve the extrusion of large molecular fragments that can limit the processing of these polymers or produce very sensitive and even explosive materials. Therefore, a forgiving and direct route to PA and substituted PA, such as ring opening metathesis polymerization (ROMP), which might lead to new substrates and amenable processing conditions is worth pursuing. The metathesis polymerization of 1,3,5,7-cyclooctatetraene (COT) has been reported previously, however, the only successful routes to date have focused on early transition metal catalysts (tungsten) which are sensitive to air, moisture, and functional groups. It would be advantageous to use a late transition metal catalyst (ruthenium) which is more tolerant towards air, moisture and functional groups. Unfortunately, the RuCl_2(☐CHPh)(PCy_3)_2, catalyst 1, was not able to polymerize COT presumably due to its lower activity. Here, we report the ROMP of COT by a highly active well defined ruthenium olefin metathesis catalyst, RuCl_2(☐CHPh)(PCy_3)(IMesH_2), catalyst 2, to produce films of polyacetylene (PA) with conductivities comparable to those first produced by Shirakawa.