Reactions of Cp 2M(PMe 3) 2 complexes (M = Ti, Zr) with acetylenes. Selective formation of trans-polyacetylene at low temperatures

Abstract

The reaction of Cp 2Ti(PMe 3) 2 with C 2H 2 gives the substitution product Cp 2Ti(C 2H 2)(PMe 3), the titanacyclopentadiene Cp 2Ti(C 4H 4), and trans-polyacetylene. A mechanism for the catalytic formation of polyacetylene is proposed. Substituted acetylens R 1C 2R 2 (R 1 ≠ R 2 = H, Me, Ph) react with Cp 2Ti(PMe 3) 2 in an analogous manner except that no polyalkynes are produced. The Zr derivative Cp 2Zr(PMe 3) 2 and C 2H 2 yield the labile Cp 2Zr(C 2H 2) (PMe 3).