Reactions of 1-Titana- and 1-Zirconacyclopent-3-ynes with Tris(pentafluorophenyl)borane^†

The 1-metallacyclopent-3-ynes Cp2Ti(η4-H2C4H2) (1) (Cp = η5-cyclopentadienyl) and rac-(ebthi)Zr(η4-H2C4H2) (2) (ebthi = 1,2-ethylene-1,1‘-bis(η5-tetrahydroindenyl) react with B(C6F5)3 under ring opening of the metallacycle and formation of the zwitterionic complexes [Cp2Ti]+−CH2C⋮CCH2−[B-(C6F5)3] (3) and [rac-(ebthi)Zr]+−CH2C⋮CCH2−[B-(C6F5)3] (4). Crystal structures of 3 and 4 show a but-2-yne-1,4-diyl ligand bridging the metallocenium center and the formed boranate. Complex 4 is an active catalyst for ethylene polymerization.