Cyclotrimerization and Polymerization of 1-Hexyne Catalyzed by Group 5, 6 Transition Metal Chlorides

Abstract
1-Hexyne could be cyclotrimerized selectively and quantitatively by NbCl5 and TaCl5. The cyclotrimer formed consisted of 1,2,4- and 1,3,5-isomers. The 1,2,4/1,3,5 isomer ratio of the product was about 70/30–80/20 with NbCl5, and about 55/45–70/30 with TaCl5. The polymerization of 1-hexyne by MoCl5- and WCl6-based catalysts afforded a methanol-insoluble polymer and methanol-soluble products in comparable amounts. The polymer (mol wt 3000–5000) was an orange-yellow viscous material with structure [ \llap–CH=C(n-Bu) \llap–]n. For comparison, the cyclotrimerization and polymerization using Ziegler catalysts were also examined.