Initiation of polymerization of phenylacetylene with WOCl4 and WCl6 "single-component" metathesis catalysts

At low monomer-to-catalyst mole ratio (3:1) in benzene or toluene, phenylac etylene (PhA) reacts with WOCl4 to arylderivatives belonging to five homolo gous series with increment equal to PhA unit, low amount of chloroderivativ es and traces of PhA oligomers, mainl cyclotrimers. Aryls built in the deri vatives originate from the solvent used. Hydrogen transfers between PhA uni ts were found to participate in the overall reaction. An increase in the Ph A/WOCl4 mole ratio results in a lowered yield of arylderivatives, higher yi eld of cyclotrimers and formation of highe PhA oligomers (ratio 12:1) o pol y( phenylacetylene) (ratio 100:1). Chloroderivatives are formed in comparab le amounts at any PhA/WOCl4 mole ratio so that they can be regarded as the key byproduct of reduction of WOCl4 to low-valent tungsten species. In reac tion systems with the mole ratio up to 12: 1, WOCl4 is transformed into bla ck solid assigned to WOCl2. It dissolves in PhA inducing its polymerization in which only PhA cyclotrimers are the side products. Formation of aryl- a nd chloroderivatives as well as tungsten growing species is discussed in te rms of reaction pathway presuming an important role of oxo ligand of tungst en species. Reaction of PhA wit WCl6 results in a formation of various PhA chloroderivatives and a fine precipitate of reduced tungsten species, which polymerizes PhA after poorly reproducible induction period.