Real-time mid-IR monitoring of metathesis reactions by fiber optic FTIR spectroscopy

The real-time monitoring of metathesis reactions using a recently developed fiber optic transmission FTIR technique is reported in this paper. The ring-opening metathesis polymerization (ROMP) of 1,5-cyclooctadiene, the ring-closing metathesis (RCM) of 1,7-octadiene and the polymerization of phenylacetylene were investigated. The Schrock carbyne complex, Cl3(dme)WCCMe3, was used as the catalyst for these reactions. The phenylacetylene polymerization was also studied with WCl6 as the catalyst. In the ROMP of 1,5-cyclooctadiene, monomer consumption was followed by monitoring the disappearance of the 1486 cm−1 absorbance, characteristic of the CH2 deformation vibration (δs CH2) in the monomer. In the RCM of 1,7-octadiene, conversion data was obtained by monitoring the 1832 cm−1 signal, which is an overtone of the wagging absorbance at 910 cm−1 of the CH2 end group in the monomer. Phenylacetylene polymerization was monitored by the disappearance of the ν –CCH stretch signal at 2110 cm−1. Polymerization was much faster with the Schrock catalyst than with WCl6, but similar conversions were reached in both reactions. Conversion data obtained by the IR technique agreed well with gravimetric product yields.